3.1. MICROHABITAT OF PABO CATFISH

Transcription

1 3.1. MICROHABITAT OF PABO CATFISH Introduction: The exact position chosen by the individual appears to be related to physical characteristics especially depth, water current and substrate (Allee et al., 1949; Chapman and Bjorm, 1969) which has been termed as microhabitat. Though Ompok pabo is an endangered species (Datta et al., 2003; NBFGR, 2010), its population is plenty in certain pockets of Assam including Goronga beel of Morigaon district. Fish requires specific areas for reproduction and recruitment success depends on favorable environmental conditions for the survival of the larvae and juveniles (Urho, 1999). For conservation of any species, the information regarding the natural habitat is prerequisite on the basis of which the artificial propagation can be initiated. Habitat use, selection, and preference of fishes are important information to fisheries managers. Habitat use is simply what habitat a fish is occupying. Habitat selection requires knowledge of what habitat is available, which is then compared to habitat used to determine selection. Habitat preference is similar to habitat selection, except that all possible habitat variables must be available in order to determine preference; this usually limits habitat preference studies to laboratories with strictly controlled parameters (Rosenfeld, 2003). Environmental factors and habitat settings can affect fish distribution at multiple scales, ranging from a bio-geographical perspective to species-specific microhabitat use in local communities (Reichard, 2008). Therefore, investigations were carried out to understand the exact profile of habitat used by the Pabo catfish Microhabitat of the species: The Microhabitat of Ompok pabo were carried out from The species is a bottom dweller one and prefers to live in shoal. The fish prefer sandy soil with low velocity water current. It has been observed in the beel that fishes are carnivorous in nature and in addition to that occasionally they prefer to eat decomposed bark of fallen trees locally known as Sarua (Streblus asper Lour) (Sarma et al, 2012). Apart from this, other food items which were observed in the gut of the fishes were small [66]

2 fish, prawn, moluscans, chironomids, Tubifex worm etc. It has been observed that Ompok pabo prefer to made their niche with another catfish Pseudotropius atherinoides at the Goronga beel. Fishing of Ompok pabo was carried out by the fisherman after making a suitable region (deep area) which is known as jeng or katol. This is constructed by protecting a region with net of appropriate size where some tree branches and maximum floating weeds i.e. Echornia sp., pistia sp. etc. are dumped. As high aquatic weeds give a suitable environment for aquatic insect; Pabo along with some other cat fishes are attracted to this region. After 10 to 15 days, fishing is done at this jeng which gives a high catch of Pabo fish. This is the main reason for which this jeng is called as also Pabho jeng. Fishing of one Pabho jeng could give a catch of 4 to 8 kg Pabo fish at a time. However, Pabho fishing was found restricted only to 7-10 times in an annual cycle and only in winter. It might be due to the abundance of this fish only in one season (winter) per year. Every year at least Pabho jeng are raised throughout the wetland by the Mahalder (lessee) to catch Pabo besides other fish species and a total of three fishing trial are practiced in each jeng. It has been observed in three subsequent fishing trials at one Pabho jeng that the number of fish catching diminished from first to the subsequent trials (Figure 3.1.4). The Shannon- Weiner diversity index of fish population of the wetland ranged from 2.11 to Water quality of the habitat: ph value was observed between 7.9 and 8.4, highest recorded in winter season and lowest in the retreating monsoon season. The water temperature of the beel observed between the range of C and C, lowest being observed in winter and highest in Monsoon season. Transparency ranges observed between 40.2 cm and 48.9 cm where, lowest recorded in winter and highest in Retreating monsoon. DO values were observed between 8.4 mg l -1 and 12.5 mg l -1. Lowest DO recorded in winter and highest in monsoon season. Free CO 2 range between 2.2 mg l -1 and 6.4 mg l -1 of which maximum was observed in winter and minimum in retreating monsoon. [67]

3 Table Mean Value (± SD) of water quality parameters of Goronga beel Parameters in four seasons ( ) Seasons Premonsoon Monsoon Retreating Winter Monsoon ph 8.2 ± ± ± ± 0.5 Water 24.9 ± ± ± ± 1.6 temperature ( 0 C) Transparency 46.5 ± ± ± ± 3.1 (cm) Dissolved oxygen 10.2 ± ± ± ± 0.4 (mg l -1 ) Free CO ± ± ± ± 0.6 (mg l -1 ) Total alkalinity 40.5 ± ± ± ± 15.1 (mg l -1 ) Total hardness 39.5 ± ± ± ± 1.9 (mg l -1 ) Chloride (mg l -1 ) ± ± ± ± 0.58 Alkalinity value found between 40.5 mg l -1 and 75.2 mg l -1 highest in monsoon and lowest in pre monsoon. Hardness was recorded between 36.8 mg l -1 and 42.7 mg l -1 lowest estimated in retreating monsoon and highest in winter. Chloride value range was between 8.08 mg l -1 and mg l -1. Highest value of chloride was estimated in winter and lowest value in monsoon. It has been found that all the water quality parameters were within the permissible limit for the growth of fishes Aquatic macrophytes of the beel: Total of 26 aquatic macrophytes belonging to six ecological classes (Barua and Barua, 2000) were recorded in the Goronga beel (Table 3.1.2). Altogether 4 free floating macrophytes were recorded, among which Eichhornia crassipes was the dominant one. Only one species belonging to free submerged category i.e. Hydrilla verticiellata was recorded. One species of anchored submerged group was recorded i.e. Ottelia alismoides. Highest number of macrophytes (nine) were found under the group of anchored floating; which was the dominant group (Figure-3.1.1). Other macrophytes include 6 species of emergent amphibious and 5 species of marshy amphibious class. [68]

4 Table Aquatic macrophytes of the Goronga beel and its ecological class Sl. No. Scientific name Local name Ecological class 1. Hydrilla verticiellata Pani kaduri Free submerged 2. Eichhornia crassipes Bih meteka Free floating 3. Pistia stratiotes Bor puni Free floating 4. Trapa natans Singori Free floating 5. Ipomoea aquatic Kolmou Free floating 6. Nymphoides cristatum Pan chuli Anchored floating 7. Monochoria hastate Kar meteka Emergent amphibious 8. Eurayle ferox Nikori Anchored floating 9. Enhydra fluctuans Helesi saak Anchored floating 10. Ipomoea carnea Ajati kolmou Emergent amphibious 11. Nelumbo nucifera Podum Anchored floating 12. Nymphaea nouchali Bogavet Anchored floating 13. Alternanthera philoxeroides Tita helonci Emergent amphibious 14. Commelina bengalensis Kona simolu Marshy amphibious 15. Commelina diffusa Kona simolu Marshy amphibious 16. Cyperus brevifolius Sesor Marshy amphibious 17. Ludwigia adscedens Pani khutura Marshy amphibious 18. Ludwigia octavalvis Pani long Marshy amphibious 19. Monochoria vaginalis Pani meteka Emergent amphibious 20. Nymphaea alba Boga vet Anchored floating 21. Nymphaea pubescens Sindhei shelock Anchored floating 22. Nymphaea nouchali Ronga vet Anchored floating 23. Nymphoides indica Tal japori Anchored floating 24. Ottelia alismoides Segun tepa Anchored submerged Sagittaria guayanensis Sagittaria sagittifolia Pani kosu Pani kosu Emergent amphibious Emergent amphibious [69]

5 Apart from the macrophytes, the marginal grass species were Leersia hexandra, Hemarthia compressa, Cynodon dactylon, Andropogon aciculatus, Phragmites karka, Saccharum spontaneum, Imperata cylindrical, Pollinia ciliate, Arundo donax, Alpinia allughas. At the bank region, some economically important plants were found such as Hridol (Barringtonia acutangula), Azar (Lagerstroemia speciosa), Simolu (Bombax ceiba), Bogori (Zizyphus sp.) etc Ichthyofaunal diversity of the beel: A total of 77 important fish species were recorded during the period of survey (Table 3.1.3). Among these, according to IUCN status 3 species are endangered (EN), 17 species vulnerable (VU), 27 species lower risk-near threatened (LRnt), 6 species lower risk-less concern (LRlc) and other 24 species are not evaluated (NE). The taxonomic composition of the fish fauna (Figure 3.1.3) suggests Cyprinidae to be the most dominant family with 30 representative species (38.9%) occurring in the study site followed by Bagridae, the next dominant family, has 6 species (7.7%)). Beside Ompok pabo the beel was also found as homeland of some other endangered fish species like, Ompok pabda, Rasbora elanga, and Puntius sarana. Sl. No Table Fish faunal diversity of Garanga beel along with its family, annual catching percentage and IUCN status Scientific name Family Annual catching (%) IUCN Status 1 Chitala chitala (Pallas) Notopteridae 1.8 EN 2 Notopterus notopterus (Ham.- Notopteridae 1.5 LRnt Buch.) 3 Gudusia chapra (Ham.-Buch.) Clupeidae 2.1 LRlc 4 Aspidoparia jaya (Ham.-Buch.) Cyprinidae 1.6 VU 5 Aspidoparia morar (Ham.- Cyprinidae 1.4 LRnt Buch.) 6 Amblypharingodon mola (Ham.- Cyprinidae 2.5 LRlc Buch.) 7 Barilius barna (Ham.-Buch.) Cyprinidae 1.2 LRnt 8 Chela cachius (Ham.-Buch.) Cyprinidae 1.3 NE [70]

6 9 Crossocheilus burmanicus Cyprinidae 0.9 VU (Hora) 10 Chela laubuca (Ham.-Buch.) Cyprinidae 1.6 LRlc 11 Cirrhinus mrigala (Ham.-Buch) Cyprinidae 2.4 LRnt 12 Cirrhinus reba (Ham.-Buch.) Cyprinidae 0.3 VU 13 Catla catla (Ham.-Buch.) Cyprinidae 2.3 VU 14 Danio aequipinatus (Mc Cyprinidae 0.4 LRnt Clelland) 15 Danio daverio (Ham.-Buch.) Cyprinidae 1.5 LRnt 16 Esomus danricus (Ham.-Buch.) Cyprinidae 1.2 LRlc 17 Labeo bata (Ham.-Buch.) Cyprinidae 1.9 LRnt 18 Labeo calbasu (Ham.-Buch.) Cyprinidae 1.6 LRnt 19 Labeo gonius (Ham.-Buch.) Cyprinidae 0.5 LRnt 20 Labeo rohita (Ham.-Buch.) Cyprinidae 1.8 LRnt 21 Puntius chola (Ham.-Buch.) Cyprinidae 0.2 VU 22 Puntius chonconius (Ham.- Buch.) Cyprinidae 0.6 VU 23 Puntius gelious (Ham.-Buch.) Cyprinidae 0.4 NE 24 Puntius javanicus (Bleeker) Cyprinidae 0.6 NE 25 Puntius sarana (Ham.-Buch) Cyprinidae 0.2 VU 26 Puntius shalynious (Yazdani & Cyprinidae 1.4 VU Talukdar) 27 Puntius sophore (Ham.-Buch.) Cyprinidae 2.5 LRnt 28 Puntius terio (Ham.-Buch.) Cyprinidae 0.6 LRnt 29 Puntius ticto (Ham.-Buch.) Cyprinidae 0.5 LRnt 30 Rasbora rasbora (Ham.-Buch.) Cyprinidae 2.3 NE 31 Rasbora daniconius (Ham.- Cyprinidae 2.0 NE Buch.) 32 Salmophasia bacaila (Ham.- Buch.) Cyprinidae 0.7 LRlc 33 Rasbora elanga (Ham.-Buch.) Cyprinidae 0.1 NE 34 Acanthocobitis botia (Ham.- Balitoridae 0.5 NE Buch.) 35 Botia Dario (Ham.-Buch.) Cobitidae 1.7 NE 36 Somileptis gongota (Ham.- Cobitidae 0.3 LRnt Buch.) 37 Lapidocephalus guntea (Ham.- Buch.) Cobitidae 2.5 NE 38 Mystus bleekeri (Day) Bagridae 0.3 VU [71]

7 39 Mystus cavasius (Ham.-Buch.) Bagridae 0.4 LRnt 40 Mystus tengera (Ham.-Buch.) Bagridae 2.4 NE 41 Mystus vittatus (Bloch) Bagridae 2.5 VU 42 Rita rita (Ham.-Buch.) Bagridae 0.4 LRnt 43 Aorichthys aor (Ham.-Buch.) Bagridae 0.4 NE 44 Ompok pabda (Ham.-Buch.) Siluridae 1.7 EN 45 Ompok pabo (Ham.-Buch.) Siluridae 2.6 NE 46 Wallagu attu (Schneider) Siluridae 1.7 LRnt 47 Ailia coila (Ham.-Buch.) Schilbeidae 0.3 VU 48 Clupisoma garua (Ham.-Buch.) Schilbeidae 1.9 VU 49 Eutropichthys vacha (Ham.- Schilbeidae 0.4 EN Buch.) 50 Bagarius bagarius (Ham.-Buch.) Sisoridae 0.8 VU 51 Gagata cenia (Ham.-Buch.) Sisoridae 0.2 NE 52 Clarius batrachas (Linnaeus) Claridae 2.6 VU 53 Heteropneustes fossilis (Bloch) Heteropneustidae 1.4 VU 54 Chaca chaca (Ham.-Buch.) Chacidae 0.3 NE 55 Sicamugil cascasia (Ham.- Mugilidae 0.4 VU Buch.) 56 Xenentodon cancilla (Ham.- Belonidae 2.3 LRnt Buch.) 57 Monopterus cuchia (Ham.- Symbranchidae 2.0 LRnt Buch.) 58 Macrognathus aral (Bloch & Mastacembelidae 1.7 LRnt Schneider) 59 Macrognathus puncalus (Ham.- Mastacembelidae 2.2 LRnt Buch.) 60 Mastacembalus armatus (Lacepede) Mastacembelidae 2.5 NE 61 Chanda nama (Ham.-Buch.) Chandidae 2.1 NE 62 Chanda ranga (Ham.-Buch.) Chandidae 1.5 NE 63 Badis badis (Ham.-Buch.) Nandidae 1.3 NE 64 Nandus nandus (Ham.-Buch.) Nandidae 0.7 LRnt 65 Glossogobius giuris (Ham.- Gobiidae 2.2 LRnt Buch.) 66 Glossogobius gutum (Ham.- Gobiidae 0.3 NE Buch.) 67 Anabas testudinius (Bloch) Anabantidae 2.4 VU 68 Colisa fasciata (Schneider) Belontidae 2.0 LRnt [72]

8 69 Colisa sota (Ham.-Buch.) Belontidae 0.7 NE 70 Colisa lalia (Ham.-Buch.) Belontidae 0.3 NE 71 Colisa labiosus (Schneider) Belontidae 0.8 NE 72 Ctenops nobilis (McClelland) Cyprinidae 0.5 NE 73 Channa marulius (Ham.-Buch.) Channidae 0.6 LRnt 74 Channa punctatus (Bloch) Channidae 2.5 LRnt 75 Channa striatus (Bloch) Channidae 1.6 LRlc 76 Channa gachua (Ham.-Buch.) Channidae 0.4 NE 77 Tetradon cutcutia (Ham.-Buch.) Tetradontidae 1.8 LRnt LRlc=Lower risk least concern; LRnt = Lower risk near threatened; VU= Vulnerable; EN= Endangered; NE = Not Evaluated. Catch unit per effort of gill net was also found uniform relative abundance (n per catch) of fish throughout the wetland during the period of investigation. Catching of fishes is only entitled to those fishers, who are dealing with the Moholdar (lessee). A total of 60 to 100 fishermen involves with the fishing activity. The highest catching rate recorded was 600 kg/day while lowest recorded as 25 kg/day through various fishing gears used in the wetland Aquatic macro-invertebrates: Macro-invertebrates of the beel belong to Annelids, Gastropod, Odonata, Ephemeroptera, Diptera, Hemiptera, and Coleoptera. Depending upon the degree of association of macro-invertebrates with aquatic macrophytes; they can be classified into two major groups: a) The fauna closely associated with submerged macrophytes (i.e. Annelids, Chironomids, Odonata and Ephemeroptera) were recorded. b) Other comparatively less associated or generally not moving types (Gastropoda, Hemiptera, and Coleoptera). Both adults and larval forms of Mayflies (Ephemeroptera), Caddis flies (Trichoptera), Midges (Diptera), Mosquito larvae, Chironomids, Water bugs like Notonecta, Nepa etc. were also found. [73]

9 3.1.7 Fishing gears used at the beel: A good number of fishing gears are used in the beel in different seasons. Among the fishing gears used, some are used in the beel almost all the times except monsoon season i.e. in breeding season due to government ban on fishing. The main fishing gears operated at the beel are summarized in Table Table Fishing gears operated in Goronga beel Sl. No. Gears Nature of fishing 1 Drag net (Ber jal) Operated when fishing in the jeng during winter season 2 Gill net (Kareng jal) Operated throughout the year 3 Hooks (Khuti borosi) Hooks are used to catch mainly Rita rita and Wallago attu throughout the year 4 Gill net (Fasi jal) Operated during monsoon season against water current 5 Dip net (Doli or Basuri jal) Operated throughout the year in all sites of the beel 6 Lift net (Khora jal) Operated in all season for all type of fish 7 Cast net (Sewali jal) Operated in all season for all type of fish [74]

10 Figure Different aquatic macrophytes (%) recorded in the beel 31% 4% 22% 8% 35% EN VU LR-nt LR-lc NE Figure IUCN status of fish fauna recorded from the Goronga beel [75]

11 No of species Notopteridae Clupeidae Cyprinidae Balitoridae Cobitidae Bagridae Siluridae Schilbeidae Sisoridae Claridae Heteropneusti Chacidae Mugilidae Belonidae Synbranchidae Mastacembeli Chandidae Nandidae Gobiidae Anabatidae Belontidae Channidae Tetradontidae Family Figure Family wise distribution of fish fauna of the Goronga beel Mean Pabho catching (Kg) st trial 2nd trial 3rd trial No of Pabho Jeng considered Fig Pabo catching record in three subsequent fishing trials at Pabho jeng [76]

12 PHOTO PLATE: I Photo 1.1 View of Goronga beel showing live Pabho fish stocking Photo 1.2 View of Goronga beel showing Katol (Pabho jeng ) [77]

13 PHOTO PLATE: I (CONT ) Photo 1.3 View of Goronga beel showing Pabho fishing at jeng Photo 1.4 Water quality analysis of Goronga beel microhabitat [78]

14 3.1.8 Discussion: Microhabitat can be defined as the exact location and condition where an animal spend all or a portion of its time (Shirvell and Dungey, 1983). The place is presumably chosen by the fish in respond to proximate factors to optimize its net energy gain (Fausch, 1984), while avoiding predators and minimizing interactions with competitors (Baltz et al., 1987). From the investigation, it has also been observed that Ompok pabo is mostly acquainted with the low velocity running water ecosystem. Occurrence of this endangered species in the Goronga beel may be due to having constant low velocity current generated from inlet and outlet of the beel. 26 species of recorded aquatic macrophytes can provide habitats for different insect s population (Table 3.1.2). Gut content analysis of Ompok pabo reveals that the species is also a piscivorous as well as insectivorous in nature. Therefore, the macrophytes can provide required number of food items for carnivorous fishes. Deka (2008) reveals that the submerged and floating leaved emergent macrophytes have positive benefit; when they are in optimum condition in the wetland. According to him, they provide food, shelter and breeding environment to the wetland fishes, because of which, the fish stock have been observed high in the macrophyte infested wetlands. Present findings are also in conformity with the above that though the species of aquatic macrophytes were remarkably high, but; eutrophied condition not yet prevailed in the wetland. It may be mentioned that Ompok pabo fishing was mostly done by constructing a niche of different aquatic macrophytes particularly Eichhornia crassipes. Earlier, it was observed a total of 23 aquatic angiospermic species belonging to 16 genera under 15 families from the wetland habitat in Pobitara Wildlife Sanctuary (Ali et al., 2008). Thus, the habitat is suitable in terms of food and space availability for the species because there will be less competition among the catfishes. Occurrence of second highest number of fish in the Goronga beel under Bagridae family also provides evidence to habitat suitability in the beel. This might be the reason, why the beel is a habitat for 77 number of important fish species including 3 endangered species (Table 3.1.3). According to Kalita and Goswami (2006), the habitat suitability preference distinctly provide ecological safeguard to the silurid fish species to avoid competition with the others, inhabiting the same area. The significant of habitat preference is that [79]

15 the fish species, which form microhabitat, can live comfortably in it and use available space efficiently (Shirvell and Dungey, 1983). The Shannon-Weiner diversity index of fish population of the wetland (2.11 to 3.41) indicated a strong relationship with overall species richness of the wetland and also indicate suitable habitat for the silurid species. Baltz et al. (1987) assumed in case of stream that the variables measured to define the microhabitats used are generally those that can be measured easily both on transects and with association with the fishes such as mean water column velocity, total depth and substrate. However, in the present study; as the microhabitat was a wetland the variables measured were ph, water temperature, transparency, DO, FCO 2, total alkalinity, total hardness and chloride. All the studied physico-chemical parameters of the beel were found suitable for existing fish community (Table 3.1.1). Physico-chemical parameters are considered as the most important principles in the identification of the nature, quality and type of the water (fresh, brackish, saline) for any aquatic ecosystem (Abdo, 2005). Fish survive and grow best in waters with a ph between 6 and 9. If ph readings are outside this range, fish growth is reduced (Buttner et al., 1993). In present study, highest value of ph (8.4) in winter might be due to decomposition of aquatic vegetation in the beel. Fish will have good appetite, the highest metabolic efficiency and the fastest growth at the optimum temperature. The temperature above or below the optimum level, fish growth is reduced (Buttner et al., 1993). Present study reveals maximum water temperature in the monsoon season might be due to increasing trend of photoperiod. Same findings were also reported by Salam et al. (2000). One of the most obvious and familiar properties of water is its transparency. Highest value of transparency in the monsoon season results from increasing of light penetration in the water. Lowest transparency in winter might be due to increase of organic matter as well as heavy fishing activity in that season. According to Ali et al. (2005), light penetration shows an increase to July and then a decrease till November. The high oxygen concentrations observed in the monsoon may be due to inflow of oxygen rich water following pre-monsoon showers. Again, it may be mentioned that lowest DO in winter was due to less rainfall and increasing fishing activity during this [80]

16 time. Maximum range of free CO 2 was recorded in winter might be due to high rate of decomposition of organic matters by the microbes resulting in rapid production of free CO 2 (Sinha, 1986). Lower concentration of free CO 2 also may be due to heavy rain and higher photosynthetic action of aquatic organisms. Highest alkalinity observed in the monsoon season indicates organic decomposition of aquatic vegetation. According to Abdo (2005), the increase in the bicarbonate during autumn may be attributed to the decrease in air and water temperature, leading to decrease in the reaction rate of carbonate direction and vice versa. It has been suggested that chloride content also increased with degree of eutrophication (Sinha, 1986). Due to organic matter decomposition, chloride content increases in lakes (Vass and Zushi, 1983; Ara et al., 2003). Highest value in winter might be due to anthropogenic activity. The values of hardness were comparatively higher in the water samples collecting during dry seasons (winter), because of no rainfall at this time and the water bodies tends to accumulate the contaminates. Macro-invertebrates of the studied habitat (Goronga beel) include different species of Annelids, Molluscans, and Arthropods. It was observed that some fauna were closely associated with submerged macrophytes and others comparatively less associated or generally not moving types. Sarma et al., (2007) also reported two types of macro invertebrates from the Urpod beel of Goalpara district, Assam. These are the very important part of an aquatic ecosystem. According to Pathani and Upadhyay (2005), the biota of an aquatic ecosystem directly reflects the conditions existing in the environment in terms of the quantity and quality of the biota. As Pabo is a carnivorous fish, the presence of different macro invertebrates in the beel provides a good habitat for it. It has been observed that earthworm (Annelids) is the good food item for Ompok pabo. It may be one of the reasons why Pabo catfish population in the beel is good. Microhabitat studies reveal that the species (Ompok pabo) enjoys a suitable habitat at the Goronga beel, the studied habitat of Ompok pabo species. Though, some parameters indicate a high fluctuation throughout the year, the water of the beel still suitable for maximum growth of different fishes including Ompok pabo. Das et al. [81]

17 (2010) reported a total of 42 fish species including 7% endangered species in the beel indicates that the microhabitat is favorable for survival of fishes. However, all the parameters were found within the permissible limit for the maximum growth of fishes (Saha, 1996). Fish catching results also indicate the relative abundance of fishes in the beel. However, though no any destructive fishing devices were observed (Table ), the mesh size of all the fishing nets should be large to check the hatchling and fingerlings. Again, during the breeding season; fishing activity should be strictly banned and the fishers will have to abide by the rule for an effective conservation strategy. [82]

18 3.2. MANAGEMENT OF CULTURE POND Introduction: Aquaculture ponds are living dynamic systems; as they exhibit continuous and constant fluctuations. The pond undergoes a vast collection of both chemical reactions and physical changes. The maintenance of good water quality is essential for both survival and optimum growth of culture organisms. Water quality within an aquaculture pond is continuously changing depending on certain conditions. These behavioral changes are referred to as Pond Dynamics and must be understood if a pond system is to be managed effectively. The reproduction, growth, and development of the fish are carried out in the water; therefore, there should be a good water quality to ensure better growth and healthy survival of fishes. Fish cannot be put into ponds, left uncared, and expected to grow and provide food and income. Successful culture system requires active attention to be ensured. Water to fish does not merely serve as a solvent for life, but an indispensable habitat for fish; its degree of excellence is the most determining factor for the propagation of desirable aquatic organisms. Fish pond management however includes all management practices applied to fish ponds in order to increase the yield per unit area of pond: for example, the water quality, fertilization of ponds, feeding, stocking, stock manipulation etc. According to Khanna (1996), the productivity of the pond depends upon its soil base, and can be greatly enhanced by a) controlling the vegetation, b) cleaning the pond bottom, c) fertilization. Stocking pond management was done as per these parameters to meet the maximum growth of Pabo brood fishes Management of stocking pond: Pond was maintained as far as possible to provide better environment and health to the brood stock. Management exercises mostly deal with frequent monitoring of the pond to check fish mortality, water quality etc. If any disturbance noticed immediate correction measures were also taken. During the month October/2009 pond water was with fast growth of algal bloom as a result of which, a dark green layer was observed [83]

19 on the water surface. Preventative measures were done by following three methods (Saha, 1996). 1) By spraying raw cow dung mixing with 200kg/ha to the pond. 2) By disturbing the water surface with a bamboo stick (stirring method). 3) By stocking silver carp which is known as a plankton feeder. Dark green color of the water was decreased gradually and found normal in the last week of November. However, no fish mortality was observed during this period at the pond. It may be mentioned that minor erosion of pond dyke was noticed during the late rainy season. It was stopped by making bamboo barricade and filling the site with clay soil Disease and mortality: So far Ompok pabo brood fish is concerned, no disease or mortality was observed in the whole period of investigation. But, as one silver carp (Hypopthalmichthys molitrix) was found dead at the pond, preventative measure was taken by applying potassium 0.5 g/l to the pond twice a day for one week. Excess growth of aquatic plants along the side and floating weeds were controlled by eradicating it mechanically from the pond once in a year. The herbivorous fish like Grass carp (Ctenopharyngodon idella) was also released to control the aquatic weeds from the pond. However, aquarium rearing fishes were observed suffering from fin rot disease. As a result, the fins (pectoral fin, pelvic fin, dorsal fin, caudal fin and anal fin) were decomposed totally. It was due to the fungal infection, which finally attacked to the barbels. The maxillary pair of barbels was fully decomposed within 48 hours of infection of fins. One tablets of ampicillin-500 medicine was used twice daily at the rate of ½ of one tablet. Feeding was stopped during the treatment period. It was observed that fin rot was fully cured within four days of treatment. All the fins as well as infected barbels were regenerated completely. [84]

20 3.2.4 Physico-chemical parameter analysis of pond water: Water quality is the totality of physical, biological and chemical parameters that affect the growth and welfare of cultured organisms. Among the physic-chemical factors influencing aquatic productivity, ph, alkalinity, dissolved gases like oxygen and carbon dioxide and dissolved inorganic nutrients are considered to be important (Banerjea, 1971). Water quality affects the general condition of cultured organism as it determines the health and growth conditions of cultured organism (Mallya, 2007). The mean values of different physico-chemical characteristics for all the four seasons i.e. winter, pre monsoon, monsoon and retreating monsoon during three annual cycles are shown in the figures from to Water temperature ( 0 C): Temperature is a factor of great importance for aquatic ecosystem, as it affects the organisms, as well as the physical and chemical characteristics of water (Delince, 1992). The water temperature of the pond was observed between the range of C to C (Figure 3.2.1). In the year , the average temperature was observed maximum ( C) in monsoon season and minimum ( C) in winter season. But in it was maximum ( C) in pre monsoon and minimum ( C) in the retreating monsoon season. The ranges in the third annual cycle was between C and C It may be mentioned that the year 2008, monsoon was coming very late in Assam due to which; no rainfall was there for a long time. This might be the reason for this type of trend of temperature fluctuation Hydrogen ion concentration (ph): In all the three annual cycles, ph values of pond water were estimated between 7.9 and 8.5 (Figure 3.2.2). Lowest mean ph value was observed in winter and highest in Pre monsoon season. In the first annual cycle, the range was between 8.00 and In the second year it was between 8.03 and 8.31; while in the third year; between 7.9 and According to Banerjea (1967), water with an almost neutral reaction with ph is best suited for a fish pond and average production is expected in the range of Present studies indicated that the water of the experimental pond was on the alkaline side during the investigation period. [85]

21 PHOTO PLATE: II Photo 2.1 Water quality analysis of pond at laboratory Photo 2.2 View of algal bloom at the experimental pond [86]

22 Dissolved Oxygen (DO): According to Buttner (1993), dissolved oxygen (DO) in a culture system must be maintained above the levels considered stressful to fish. DO value in the present study was observed between the ranges of 6.8 mg l -1 and mg l -1, maximum being observed in retreating monsoon and minimum in winter (Figure 3.2.3). All the three annual cycles experienced same trend of mean DO values in the four seasons. In the , mean DO values were between the ranges of 8.94 mg l -1 and mg l -1, while in the next year; it was between 9.25 mg l -1 and mg l -1. Again, in the third annual cycle, dissolved oxygen level of pond water between the ranges of 8.55 mg l -1 and mg l Free CO 2 (FCO 2 ): Free CO 2 values were observed between 0.22 mg l -1 and 8.8 mg l -1 of which, maximum was observed in winter and minimum in monsoon seasons (Figure 3.2.4). According to Saha (1996), the acceptable standard of water FCO 2 is between the range of 1.5 mg l -1 and 15.0 mg l -1. It has been observed that the mean FCO 2 values in all the seasons of three annual cycles were having same trend of fluctuation. Mean FCO 2 values observed in the first annual cycle was between the ranges of 3.47 mg l -1 and 4.40 mg l -1, while in the next year it was between 1.48 mg l -1 and 3.34 mg l -1. On the other hand, the year showed FCO 2 values between the range of 1.67 mg l -1 and 2.75 mg l -1. However, the FCO 2 level of the pond water was suitable for culture of fish in pond Total alkalinity (as CaCO 3 ): Total alkalinity values were found between the range of 55 mg l -1 and 137 mg l -1, highest being in monsoon and lowest in retreating monsoon seasons (Figure 3.2.5). The first annual cycle experienced average alkalinity level between the range of 60.0 mg l -1 and 86.2 mg l -1. However, in the second and third cycles, it was from 79.2 mg l - 1 to 97.5 mg l -1 and 65.0 mg l -1 to mg l -1. According to Boyd (1998), the desired concentration range for bicarbonate (HCO - 3 ) alkalinity in pond water is between 50 mg l -1 and 300 mg l -1. Therefore, the present studies indicated that the pond water quality was suitable in terms of alkalinity property for aquaculture practices. [87]

23 Total acidity: Total acidity values estimated between the range of 0.66 mg l -1 and 11.0 mg l -1 of which, highest being recorded in retreating monsoon and lowest being observed in the monsoon seasons (Figure 3.2.6). In the first annual cycle ( ), mean total alkalinity observed within the range from 4.9 mg l -1 to 8.6 mg l -1, while in the second and third annual cycles, it was from 2.14 mg l -1 to 3.34 mg l -1 and 3.26 mg l -1 to 6.83 respectively Total hardness: During the period of investigation, total hardness values of the pond water fluctuated between 34 mg l -1 and 94 mg l -1 throughout the annual cycle (Figure 3.2.7). It was observed maximum in winter and minimum in the retreating monsoon seasons. However, in the first annual cycle ( ); the mean total hardness recorded between mg l -1 and mg l -1, while in the next two annual cycles, it was between the range of 50 mg l -1 & mg l -1 and 48.3 mg l -1 & 69.0 mg l -1 respectively. Normally, the preferred range of hardness for fish culture is less than 50 mg l -1 but, when it is estimated as calcium carbonate; the range should be less than 100 mg l -1 (Boyd and Tucker, 1998) Chloride: Chloride value was estimated between the range of 3.47 mg l -1 and mg l -1 of which, lowest being in monsoon and highest being in winter seasons (Figure 3.2.8). The year experienced fluctuation of chloride levels between the range of 8.23 mg l -1 and mg l -1, while it was between 4.61 mg l -1 & mg l -1 and 5.15 mg l -1 & 8.89 mg l -1 in the year and respectively. [88]

24 Mean temperature ( 0 C) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water temperature ( 0 C) in three annual cycles Mean ph Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water ph in three annual cycles [89]

25 12 Mean DO (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water DO (mg l -1 ) in three annual cycles Mean FCO 2 (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water FCO 2 (mg l -1 ) in three annual cycles [90]

26 120 Mean alkalinity (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water alkalinity (mg l -1 ) in three annual cycles 9 8 Mean acidity (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water acidity (mg l -1 ) in three annual cycles [91]

27 Mean total hardness (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water hardness (mg l -1 ) in three annual cycles Mean chloride (mg l -1 ) Winter Premonsoon Monsoon Retreating monsoon Seasons Figure Mean pond water chloride (mg l -1 ) in three annual cycles [92]

28 3.2.5 Discussion: The management of experimental pond was performed to maintain the suitable environment for the optimum growth and maturity of Ompok pabo s brood fish. Without proper maturation of brood fish, it cannot be induced to breed particularly at confined water. It is well known that reproductive processes in fishes are controlled by endogenous biological rhythms as well as by environmental cues (Munro, 1990). Physico-chemical parameters play a significant role in the maintenance of a healthy aquatic environment and production of natural food organisms (Rahman et al., 2009). Therefore, water quality management is also an important task in pond management practice. Before releasing the Pabo brood fish, potassium permanganate (KMnO 4 ) was added to the pond water as a treatment for oxygen depletion. Wilkinson (2002) reported that potassium permanganate is an oxidizing agent, which is sometimes used as a pond treatment for oxygen depletion. Apart from this, treatment of pond with potassium permanganate has been reported to substantially reduce the concentration of dissolved orthophosphate concentration (Tucker and Boyd, 1977). Again phosphorous is a key nutrient for phytoplankton and its availability limits phytoplankton growth (Hepher, 1963). Occurrence of algal bloom in October-November month might be due to excess nutrients generated through autochthonous and allochthonus source. It may be mentioned that during that period, the water level was very low because of low rainfall. This was probably the reason of eutrophication or deposition of heavy nutrients in the pond water; which induced the occurrence of algal bloom. According to Dutta Munshi & Dutta Munshi (1995), blooms of algae occurred in the summer which continued up to rainy seasons. They also revealed that Anabaena bloom remained in the pond from last week of October to 1 st week of December forming a thick carpet like structure. Occurrence of algal bloom in the present study also indicated the same trend. Preventive measures taken to control the bloom were mainly through mechanical, chemical and biological methods. On the basis of colour appearance of the pond [93]

29 water, Saha (1996) suggested to spray raw cow kg/ha or shading the surface with floating plants or disturbing the water surface. He also suggested to stock Silver carp for the control of algal bloom. By adopting his methodology, bloom was successfully controlled. It is well known that Hypopthalmichthys molitrix (Silver carp) which feeds on unicellular algae, rotifers, decaying macro vegetation, detritus etc. is a highly plankton feeder (Khanna, 1996). That is why, in the present study; this fish was used as biological control agent for algal bloom. The other methods were used only to maximize the dissolved oxygen in the pond water; which was found diminishing gradually. During the post stocking management, though there was no high fish causality in the pond; the death of only one silver carp might be due to external mechanical injury by some foreign agents like attack of fish eating birds or attack of snake. Though there was no any symptom of disease on the dead body, preventive measure was taken by treating the pond water with 4% KMnO 4. According to Swingle (1957), KMnO 4 is also sometimes used as a disinfectant or treatment of fish. However, in the aquarium occurrence of fin rot diseases might be due to fungal infection. Rapid recovery of infected fish was probably due to the strong action of antibiotic ampicilin against the fungus. Contamination of water bodies might lead to a change in their trophic status and render them unsuitable for aquaculture. Several Physicochemical or biological factors could act as stressors and adversely affect fish growth and reproduction (Iwama et al., 2000). It was observed that all the parameters were within the permissible limit and favorable for optimum growth of cultivable fish. Water temperature is one of the most important factors, which influence the physicochemical and biological events of a water body. The range of water temperature ( C to 31 0 C) recorded from the experimental ponds was within the suitable range for the culture of fishes (Boyd, 1981; Rahman et al., 2008). Besides temperature, the onset of rainfall seems to stimulate initiation of peak breeding activity (Joshi, 1987). This may be the reason for less breeding success in the session , which experienced late monsoon and rainfall. [94]

30 The fluctuation in ph of water was influenced by the acidic character of the basin soil and dense aquatic vegetation (Yadav et al., 1987) as well as by the inflowing surface runoff/floodwater. The pond water with ph of 3.6 to 5.4 has been reported to exert toxic effect on a range of fishes including mortality, reduced growth and poor reproduction (Wilkinson, 2002). The medium was neither strong nor alkaline supported by the findings of Sing (1980) and Pahwa & Melhotra (1996). Ellis (1939) observed that ph range of 6.7 to 8.4 is suitable for the growth of aquatic biota. All aquatic organisms have a certain tolerance range of ph value. Fish survive and grow best in waters with a ph between 6 and 9. If ph readings are outside this range, fish growth is reduced (Buttner et al., 1993). Thus, the pond water was mostly suitable for fish culture. Similar observation was also reported by Mollah and Hossain (1998), Rahman & Rahman (2003) and Ali et al. (2005). Decrease in ph values during cold period (winter) is mainly related to the high bicarbonate content, while the uptake of CO 2 by phytoplankton decreasing as a result of increasing in the concentration of HCO - 3 (Abdel-Satar, 2005). On the other hand, rise of free CO 2 level and dilution effect of rain perhaps reverse the ph trend during monsoon (Dey, 1981). Normally, dissolved oxygen level is low in ponds stocked with a high density of fish compared to ponds where stocking density is low. This is due to the higher consumption rate of oxygen by the higher density of fish and other aquatic organisms (Boyd, 1982). However, the DO level was within the acceptable range for fish culture (Mollah and Hossain, 1998; Rahman et al., 2005). Maximum values of DO in the retreating monsoon might be due to inflow of oxygen rich water following the monsoon showers. According to Buttner (1993), DO is changed dramatically over a 24 hour period in a pond. He assumed that during the day, oxygen is produced by photosynthesis, the process by which green plants convert water and CO 2 in the presence of light, to oxygen and carbohydrates. At higher concentrations, carbon dioxide causes fish to loss equilibrium, become disoriented and possibly die. FCO 2 concentration observed in the winter is due to decomposition of organic matters by the microbes to release free CO 2. According to Boyd (1998), the desirable limit of CO 2 is from 1 to 10 mg l -1. In the present study [95]

31 also the values recorded were within this limit. It indicates that the pond water was suitable for aquaculture. The range of total alkalinity of the study area indicate moderately alkaline can be considered as productive (Moyle, 1946). Natural waters containing 40 mg l -1 or more total alkalinity are considered as hard water for biological purposes. Alkalinity levels in the present study indicate productivity of the ponds was medium to high (Jhingran, 1991 and Rahman et al., 2005). The high values of alkalinity are indicative of eutrophic growth in the water body (Deka and Bhattacharyya, 2008). Abdo (2005) revealed that high bicarbonate alkalinity values of pond indicate their high productivity and consequently favorable contribution for fish production. It means that the water of the pond was productive and suitable for fish culture. Sometimes water shows acidity due to presence of uncombined CO 2 salts of strong acids and weak bases of mineral acids. Water normally gets acid reaction due to the organic acid resulted from high content of humus. Acidity of pond water is also related to the concentration of free carbon dioxide. It generally increased along with the increase of FCO 2 in water. The present study also reveals the same trend except in the retreating monsoon seasons. Total hardness refers to the concentration of calcium and magnesium in the water. Hard waters are generally more productive than soft waters (Durfor and Beeker, 1964). Due to organic matter decomposition, chloride content increases in lakes (Ara et al., 2000). Present findings show maximum total hardness in winter may be because of higher concentration of magnesium (Abdo, 2005). The total hardness of the pond water during investigation period was soft to moderately hard (Durfor and Beeker, 1964). The water that is higher in hardness can help to promote the normal growth of fish bone, build up fishes, digestion and absorption of food and stimulate the growth and reproduction of phytoplankton. It indicates that the pond water was mostly productive and acceptable for fish culture. [96]

32 Chloride is a common component of waters which is beneficial to fish in maintaining their osmotic balance. It is one of the major inorganic anions in water and waste water (Garg, 2003). According to Boyd (1998), pond water having chloride values from 1 mg l -1 to 100 mg l -1 is desirable for pond aquaculture. In the present study, highest chloride concentration in the winter might be due to the eutrophication of the pond water. [97]

33 3.3. MANAGEMENT OF BROOD STOCK Introduction: Successful breeding of any fish species requires quality brood stock; which can produce high quality seeds. In this regard, management of brood stock plays an important role in obtaining successful results in induced breeding. Chakrabarti et al. (2009) stated that scaling up of farming requires a consistent supply of good quality seed, necessitating captive breeding; careful brood stock management and larval rearing. According to Sahoo et al. (2010), availability of quality seed is one of the pre requisite for successful culture of any species. On the other hand, to avoid loss of genetic diversity and inbreeding depression problems in hatchery population, proper brood stock management strategies and effective breeding plans for commercially important fish species need to be designed and implemented (Hussain and Muzid, 1999). Therefore, to ensure high fry survival and reproductive success there is need to improve the sperm and egg quality through improved brood stock nutrition (Adewumi et al., 2005). The quality of sperm is highly variable and depends on various external factors such as feeding regime, the quality of the feed and then rearing temperature of the fish (Billard et al., 1995). Maturity condition of the brood fish is also a key factor for breeding success. It can be examined by observing the sexual dimorphism, which is mostly prominent in the breeding seasons. The genital pore, the size of the head, the shape of the body, abdomen of the fishes and the body coloration of both the sexes are examined for finding a practical way of discerning the sex (Musa and Bhuiyan, 2006). According to Hussain and Islam (1983), the area of genital pore is observed to be quite helpful for identification of the sexes Release of brooders to the pond: Brood fishes already collected and transported to the experimental pond were released to the pond after treating with 5% KMnO 4. It may be mentioned that brooders were cultured in the polyculture pond. During transportation period, no mortality or weakness of the brood fishes were observed. After releasing the brood fishes, constant [98]

34 observation was made to check the abnormal behavior and probable disturbance at pond environment. Pond water temperature was found almost same (20 0 C) with the source water with brood fish. All the fishes were in good condition. However, five brooders were also kept in an aquarium for studying behavior under controlled environment Feeding to brood fish: Food is the main source of energy and plays an important role in determining the population levels, rate of growth and condition of fishes. Food and feeding habits of fishes have a great significance in aquaculture practice. It helps to select such species of fishes for culture which will utilize all the available potential food of the water bodies without any competition with one another but will live in association with other fishes (Begum et al., 2008). Pabo is omnivorous and feeds on small fishes, protozoans, crustaceans, algae, insects and debris (Bhuiyan and Islam, 1991; Taleb et al., 1991). The ingredients and composition of food items were as follows: 1) Campus cultured earth 25 to 30 g/kg body weight (after cutting in to small pieces). 2) Formulated feed (rice bran 55%, m. oil cake 30%, molasses 10% and dry fish powder 45 to 50 g/kg body weight. 3) Live small fishes like Puntius sp., Rasbora sp. etc. which are already in the pond. Most of the time it was provided externally through bag 200 g/kg body weight. 4) Formulated pellet of mixed silk worm pupae and rice 100 to 150 g/kg body weight. It was noticed that the aquarium Pabo also took tadpole larva (24 hours old) occasionally. Mustard oil cake was also given to the aquarium 12 g/kg body weight, but it did not accept which might be because of its carnivorous nature of feeding. [99]

35 PHOTO PLATE: III Photo 3.1 Collection of brood fish from Goronga beel Photo 3.2 Brood fish packaging with oxygen for transportation [100]

36 PHOTO PLATE: III (CONT ) Photo 3.3 Brooders reaching at the experimental pond site Photo 3.4 Releasing of brood stock in to experimental pond [101]

37 3.3.4 Growth and maturity of the brood fishes. It has been observed that both length and weight of Ompok pabo were showing expected results. Even the color of the fishes were also retained same (in confined system) that were in their natural habitat. It was found that the confined system i.e. the pond was almost favorable for the growth of the species. On set of gonadal maturity of Pabo was observed at the age of one year in the captive condition. Till the month of February, sex was not easily distinguishable. At the month of March, it was found distinguishable as the belly of the female got enlarged; while the male developed slightly rough pectoral fin (Table 3.3.1). Enlargement of the belly of the female was more and pectoral fin of the male was found serrated. Maturity of Pabo brood fish was attained at the age of about one year in the stocking pond after rearing of six months. Maturity of gonads was initiated from the first week of May to last part of August. Fully matured brood fishes were from 21.0 cm to 23.7 cm in total length; while the weight measured between the ranges of 65.0 g and 75.0 g. Breeding efficiency was found from the month of late May to July at the favorable climatic condition. But, it may extend up to the month of August depending upon the onset of monsoon. It may be mentioned that the maturity could be easily detected in the breeding seasons due to prominent sex differences. Month Table Brood fish culture and observed maturity condition Length attain (cm) Weight attain (g) Male Maturity condition Female Jan Not distinguished. Not distinguished. Feb Not distinguished. Not distinguished. Mar Pectoral fin slightly rough. Enlargement of belly slight. Apr Slightly serrated pectoral fin. Enlargement of belly continued. May Rough pectoral fin Swollen abdomen with reddish anus. Jun Freely oozing milt with slight pressure on the abdomen. Bulging abdomen demarcated as two lobes. [102]

38 PHOTO PLATE: IV Serrated Pectoral Fin Pointed Genital Papilla Pectoral fin smooth Soft bulging abdomen Demarcation line of ovary Swollen and reddish genital papilla Photo 4.1A. Male Brood Fish. Photo 4.1B. Female Brood Fish (The bar indicates 3 cm in length) [103]

39 3.3.5 Sexual dimorphism: It has been observed that the adult Pabo showed sexual dimorphism. Sexual dimorphism of Males and females could be fully distinguishable from the month of May. Pectoral fins of male become rough and serrated, the genital papilla pointed and narrow with freely oozing milt; while applying slight pressure on the abdomen. In case of female, the pectoral fin was smooth and genital papilla was found swollen and reddish in color. The abdomen was soft and bulging in appearance. Maturity of female also can be determined by observing the demarcation line of two lobe of the ovary. This line will be very prominent in the high maturity stage. The size of the female was generally broader and bigger comparing to the male Discussion: The brood stock management was satisfactory to get the maturity of the Ompok pabo brooders; which were later induced to breed in captive condition (Table 3.3.1). At the time of releasing, no brood fish mortality was observed which might be due to the sufficient oxygen supply and maximum water limit maintained and changed twice during the transportation by motor vehicle. Water of the brood fish container was changed to minimize the stress on the brooders. Faeces, urea and ammonia produced during digestion deteriorate water used for transport (Sarma et al., 2009). On the other hand, treatment with KMnO 4 also reduced the risk of mortality. The quality and quantity of feed as well as feeding regime are important for spawning as well egg quality (Haniffa, 2009). In the present study, the brood fishes were fed with earth worm, formulated feed (rice bran, mustered oil cake, molasses and dry fish powder), live small fish, formulated pellet of mixed silk worm pupae and rice polish for a period of six month up to the maturity stage. Mukherjee et al. (2002) also used mustered oil cake and rice bran in the ratio of 1:1 for the Ompok pabo brood fish. After this stage, brooders were fully matured for induced breeding operation. Sarkar et al. (2006) maintained the brood stock of Chitala chitala in a polyculture system fed with small life prawn, trash fishes, rice bran and mustered oil cake (2:1) up to 4 months, after which they were enough matured for captive breeding. The success on good scientific planning and management of fish species largely depends on their [104]

40 biological aspects, in which food and feeding habits include a valuable portion (Joadder, 2006). There is an inverse relationship in feeding and breeding cycles (Pantulu, 1961; Pandian, 1966). For management of Ompok pabda brood stock, Chakrabarty et al. (2009) used trash fish and boiled chicken viscera at about 5-10% of total body weight/day. Das (2002) also used a mixture of trash fish and rice bran at 9:1 proportion at about 10% of the body weight of the stocked fish daily. However, in the present study, the main food item used was the earth worm as it contains all the essential amino acids required in fish feed (Kumar et al., 2007). The methionine and lysine availability in earth worm meal is higher than that of fish meal (Kumar et al., 2007). Maturity of Ompok pabo was observed after rearing for six months; which indicates a speedy growth might be due to the supply of highly proteinous food items to the brood fishes. Cyclic changes studied in relation to different maturity condition monthly for six month till the breeding experiments. At the complete maturity stage, growth was satisfactory in terms of length and weight attained i.e cm and g respectively. Maximum breeding efficiency in the months from late May to July was observed due to suitable temperature as well as monsoon rain which made the climate favorable for breeding. Similar observations were also reported by Mukherjee et al. (2002) in case of Ompok pabo. Temperature may modulate hormone action at all levels of the reproductive endocrine system, affecting the different phases of fish reproduction and especially ovulation and spawning (Suquet et al., 2005). Brood fish of Clarias batrachus was found matured at the end of first year according to Das (2002). Chakrabarty et al. (2009) also reported same results in case of Ompok pabda rearing for induced breeding operation. For breeding and culture purposes, it is necessary to separate males and females rapidly and accurately by the external characters (Musa and Bhuiyan, 2006). According to Haniffa (2008), before attempting induced breeding experiments, the fish farmers have to confirm whether the brooders are ready for spawning. Sexual dimorphism of Ompok pabo was fully distinguishable in the breeding season (from the month of May to late July). It indicates that Pabo brood fishes were ripe and ready [105]

41 for spawning. In Ompok pabda, females can be distinguished by a rounded, fuller abdomen, reddish vent colour and rounded genital papilla, while males have an elongated and pointed genital papilla (Chakrabarty et al., 2009). Mukherjee et al. (2002) reported that matured males have a rough first ray in the pectoral fin at the lower side and have a narrow and rather pointed genital papilla, which releases white milt if slight pressure is applied to the abdomen. On the other hand, females have a smooth pectoral fin and the genital papilla has a thick muscular round opening. Present findings on sexual dimorphism in Ompok pabo also show similar kind of distinct sexual differentiation. It has been found that many of the catfishes show more or less same type of sexual dimorphism. In the female Clarias batrachus, the genital papilla is short, oval and slit like; whereas in males, the papilla is conical and elongated with a pointed reddish tip (Das, 2002). According to Mahapatra (2004), a fully mature female Clarius batrachus looks a bit heavier as its abdomen is distended with eggs. Similar observation was also noticed in mature Ompok pabo as a demarcation line between two lobes of ovaries. Choudhory (1959) reported roughness of pectoral fin during breeding season in male IMC, which is a secondary sexual character. The most frequent secondary sexual difference is that of size between the sexes (Nikol skii, 1963). Present findings are also in conformity of these characteristics of sexual differences. [106]

42 3.4. BREEDING BIOLOGY Introduction: Knowledge of reproductive biology of fish is essential for evaluating the commercial potentialities of its stock, life history, culture practice and management of its fishery (Doha and Hye, 1970). The brood fish that are obtained from the wild and taken to captivity or reared in captive conditions may receive inappropriate environmental cues for reproduction and these can cause reproductive development to be arrested in late vitellogenesis (Marimuthu et al., 2009). Reproduction in fishes is regulated by environmental factors, which induces internal factors, responsible for reproduction, to become active (Bhuyan, 2003). The spawning activity is either controlled by rearing the fish in an appropriate and controlled environment for a particular species or by injecting hormone to change the internal regulatory factors (Rottmann et al., 1991). For this reason, hormonal treatment has been attempted for stimulating of gametes maturation and has been successfully used to spawn many commercially important fish species that exhibit arrested reproductive development (Zohar and Mylonas, 2001). Sahoo et al. (2007) stated that induced spawning may be a dependable alternative for obtaining high quality seed materials. Some of the fishes reproduce in natural environmental conditions that are almost impossible to initiate in a hatchery. These fishes can be made to breed in confined water or in hatchery only by administration of hormone. Ompok pabo is a fish which can not breed naturally in captive condition. The breeding performance is an important parameter to evaluate the breeding success in captive condition, which depends on the type of hormone used and its potency, dose of hormone and maturity status of the fish (Sahoo et al., 2008). Therefore, it was induced to breed by synthetic hormone injection. The commercially available synthetic inducing hormone in readymade form (ovaprim etc.) are becoming very popular and found to be efficient in successful spawning of fishes (Nandeesha et al., 1990; Cheah and Lee, 2000; Brzuska, 2001, Olubiyi, 2005). On the other hand, ovatide; which is an injectable inducing hormone also efficient in induced spawning (Sahoo et al., 2005). [107]

43 In fish production under controlled conditions attempts are made to obtain eggs of the highest weight possible and of the best quality, and hence to produce the highest possible number of good hatch (Brzuska, 2003). However, it is highly needed to develop a standard breeding technique which can then be used to conserve threatened as well as endangered fish species through captive breeding programs. Mukherjee et al. (2002) had applied artificial reproduction techniques to establish an endangered fish species breeding programme Induced breeding experiments: The breeding performances of Ompok pabo in different trials are summarized in Table The experiments were carried out for a period of three years from at the pond located in the Goalpara college campus. A total of nine breeding experiments were carried out in three breeding seasons. However, due to less rainfall and high temperature (fluctuate between the range of 30 0 C and 39 0 C) in the year 2009, breeding practices of Ompok pabo has been severely affected. Only two breeding practices could be possible during that year. In the year 2008, four breeding operation were conducted taking different male and female ratio. Two doses of hormone injection was used both for male and female brood fish separately. The synthetic hormone ovatide was used as inducing agent for breeding. For female it was 0.6 ml/kg body weight, while in case of male it was 0.5 ml/kg body weight. The latency period of spawning was observed between the range of 9.5 and 10.5 hours after injection. Fertilization rate was observed between the range of 68.2% and 76% (Figure 3.4.1). Hatching rate was fluctuated depending upon the condition of the incubation unit. It was recorded between the range of 40.5% and 45.8%. Like IMC (Indian Major Carp) breeding 2:1 (2 male and 1 female) sex ratio was found suitable in terms of spawning performance and high fertilization rate. The average survival rate was observed as 48.5%. However, about 3,236 hatchlings were recorded in the year 2008; about 1,500 fry could be able to transfer to nylon hapa fixed in the pond for further rearing. [108]

44 In the next year (2009), only two breeding experiments were done because of late gonadal maturity as well as high temperature. The earlier dose of hormone injection was slightly increased to 0.6 ml/kg body weight for male and 0.7 ml/kg body weight for female. The Average latency period observed was from 10.5 to 11.5 hours after injection. Fertilization rate was recorded between the range of 72.6% and 73.4%. However, a total of 2,608 spawns were recorded with an average hatching percentage of 41.40%. Among all these hatchlings only 470 hatchlings were survived (average 35.3%) and finally cultured at the stocking pond. In the year 2010, three breeding experiments were conducted and all the sets were bred successfully in captive condition inducing with ovatide hormone injection. Dose of hormone injection was 0.5 ml/kg body weight for male and 0.6 ml/kg body weight for female. Females were found with complete spawning. Latency period was recorded hours after the injection. Fertilization rate of the eggs was found between the range of 78.6% and 85.1%. Again hatching rate was recorded from 44.8% to 50.1% (Figure 3.4.2). A total of about 7,972 hatchlings were hatched out with an average hatching percentage of 51.08%. However, percentage of survival was recorded slightly higher (average 52.4%) than earlier experiments (Figure 3.4.3). About 2,300 fingerlings were released in to the earthen pond for further rearing. [109]

45 Figure Percent fertilization rate in different breeding trials Figure Percent hatching rate in different breeding trials Figure Mean survival rate (%) in three breeding seasons [110]

46 Table Breeding performance of Ompok pabo in different trials ( ) Year Size of male Size of female Hormone L(cm) Wt(gm) L(cm) Wt(gm) dosage (ml/kg BW) M F-0.6 M-0.6 F-0.7 M-0.5 F-0.6 Latency period (hrs) No. of eggs spawned Fertilization (%) Fertilized eggs Hatching (%) No. of hatchlings 10, , ,236 8, , ,608 20, , ,972 [111]

47 PHOTO PLATE: V Photo 5.1 Intra-muscular hormone injections to Brooders Photo 5.2 Brooders ready for hapa breeding [25]

48 PHOTO PLATE: V (CONT ) Photo 5.3 Brooders released to the hapa for breeding Photo 5.4 Collection of fertilized eggs from the hapa [26]

49 3.4.3 Water quality of breeding system: For the management and to provide better water to the matured brood fish as well as to know the water quality for good breeding performance estimation was conducted for the main parameters (Water temperature, ph, DO, FCO 2, Alkalinity, Acidity, Hardness and Chloride). Parameters were estimated in four experimental sites such as brooders pond, breeding pool, incubation tub at laboratory, nursery rearing pond. Among all the sites, the rearing tub at the laboratory was found very important as at this rearing stage maximum larval mortality occurs. The newly hatched larva was very much susceptible to the water of rearing system. A slight fluctuation of parameter value was found causing high mortality of larva. However, all the parameters were found within the acceptable range for fish culture. It has been observed that the mortality risk decreased remarkably after the larva attaining fingerling size. At this sage they can be cultured easily in the earthen pond. The water temperature was fluctuating between the range of 29.3 to C, but it was maintained at 29.3 ± 2 0 C so that; larval mortality can be minimized. The ph value was found almost alkalic (7.9 to 8.2) in the entire rearing unit. However, it was managed at 7.9 ± 0.1 as far as possible at the rearing tub in the laboratory. Dissolved Oxygen level was maximum at the breeding pool water (10.54 mg l -1 ). It might be due to continuous showering at the pool. High amount of DO is also required for effective breeding condition. Minimum but acceptable (9.26 mg l -1 ) amount of dissolved oxygen was recorded at the brood fish stocking pond. Free CO 2 level was observed between the range of 2.2 to 4.4 mg l -1. Alkalinity was found maximum (90 mg l -1 ) at the nursery rearing pond while it was minimum (75 mg l -1 ) at brood fish stocking pond. High amount of alkalinity at the nursery rearing pond may be due to residual food substance and high amount of excreta. Acidity level was within the acceptable limit (2.2 to 6.6 mg l -1 ) at all the experimental sites. Hardness values were estimated from 49 to 58 mg l -1 where it was found maximum at brood fish stocking pond. Regarding chloride content it was found maximum (8.77 mg l -1 ) at nursery rearing pond and minimum (7.89 mg l -1 ) at breeding pool water. It may be mentioned that all the though all the parameters were within the permissible limit for fish culture, special [27]

50 quality of water is very much essential for successful nursery rearing of Ompok pabo hatchlings. Table Water quality parameters during pre and post breeding experiments Sl. No. Parameter Brooders pond Breeding pool Incubation unit Nursery rearing unit 1 Temperature ( 0 C) 30.0 ± ± ± ± ph 8.2 ± ± ± ± DO (mg l -1 ) 9.26 ± ± ± ± FCO 2 (mg l -1 ) 2.2 ± ± ± ± Alkalinity(mg l -1 ) 75 ± 8 85 ± 6 80 ± 7 90 ± 5 6 Acidity (mg l -1 ) 6.6 ± ± ± ± Hardness (mg l -1 ) 58 ± ± ± ± Chloride (mg l -1 ) 8.52 ± ± ± ± Discussion: From the investigation it can be clearly understood that June month is the best and favorite month for breeding of Ompok pabo. The period from 10 th June to 20 th June the breeding attempts were fully successful. It might be due to onset of monsoon season followed by continuous rain. Chakrabarty et al. (2009) revealed that spawning of Ompok pabda occurs once in a year during the monsoon season (June August) with a peak in July. But in the present study, no breeding was observed during the month of August. Altogether eight breeding trials were carried out in captive condition. All the trials were successful with medium to high spawning, fertilization and survival rate. Breeding success mostly depends upon the health condition of the brooders. Selection of proper brooders for breeding purpose is not less important, since success in spawning and obtaining healthy progeny depends largely on proper selection of brood fish (Chaudhuri, 1959). So, as far as possible healthy brooders were taken in to consideration for breeding. Adebayo (2006) assumed that a healthy fish free injuries [28]

51 disease should be used to ensure good spawning results. It may be mentioned that breeding performance normally depend upon the synthetic hormone (ovaprim and ovatide) used. In Ompok pabda, the synthetic hormone ovatide was of very effective in the breeding comparing to that of ovaprim (Roy et al., 2007). In the present study also, latency period was found lowest in case of ovatide breeding. On the other hand, fertilization rate and hatching rate were observed high when ovatide was used for inducing Ompok pabo. According to Goswami and Borthakur (2007), ovatide is highly effective in induced breeding of Ompok bimaculatus in captivity. In every breeding season, fresh hormone was administered to minimize the risk of breeding failure. It may be mentioned that due to the low viscosity of ovatide, it can be used directly without diluting. It is therefore more preferable than other agent like ovaprim. Mukherjee et al. (2002) used ovatide and pituitary gland extract for the captive breeding of Ompok pabo in which ovatide gave the best results, with the number of eggs released 80% higher than that of from pituitary extract. In their experiments, hatching percentage was higher in ovatide and 28% higher than the pituitary extract. In the present study, the dose of 0.5 ml/kg body weight for male and 0.6 ml/kg body weight for female was proved to be the best dose in terms of breeding success rate. Chakrabarty et al. (2009) applied 1.5 ml/kg body weight for females and ml/kg body weight for males, in a single injection for Ompok pabda breeding. Mukherjee et al. (2002) used 3.0 mg/kg body weight only for female Ompok pabo brooders. Appropriate combinations of the proper dose of inducing agent and stripping yield maximum egg output during induced breeding. According to Mahapatra (2004), for induced breeding of Clarias batrachus the ideal dose of ovaprim hormone is 0.75 ml and 2.0 ml/kg body weight for males and females respectively. Vijaykumar et al. (1998) applied a single dose 0.5 ml/kg body weight to both males and females of Heteropneustes fossilis. In Channa punctatus, significantly highest fecundity was obtained in fish administered with 0.4 ml/kg BW, those injected with 0.2 ml/kg body weight and 0.6 ml/kg body weight of ovatide respectively. Disposable insulin syringes having small sized needle were used for hormone injection to minimize injury at the time of injection. Das (2002) used hypodermic syringe with a small size needle (No. 24) to inject hormone in to the [29]

52 muscle of Clarias batrachus brood fish. In conducting controlled fish reproduction particular attention should be paid to the reduction of stress threatening the spawners during numerous manipulations accompanying it (Brzuska, 2004). Though all the breeding sets showed good response to synthetic hormone; fertilization rate, hatching rate and survival rate was very low in ovaprim administration. For all the breeding experiments, generally cloudy as well as rainy days were preferred because successful spawning in majority of fishes has been induced on cloudy and rainy days, especially after heavy showers (Chaudhuri, 1969). Lower fertilization rate in the year 2008 might be due to higher temperature (30 0 C to 39 0 C) as well as late gonadal maturity. At the same time in the other seasons it was comparatively higher. Comparatively higher temperature may cause low spawning as well as fertilization rate. Sing et al. (2010) reported that prolonged exposure of fish to different photoperiod and high temperature seem to be responsible for testicular regression. The fertilization rate in the year 2009 was less due to increasing air and water temperature during day hours. A suppressive effect of high water temperature and long photoperiod on gonadal activity was demonstrated in a cyprinid fish, Gnathopogon caerulescens (Okuzawa et al., 1989). The fertilization rate depends on the egg size, which is thought to be one of the most important indices for estimation of subsequent survival and development of fry (March, 1986). Rainfall is another factor responsible for breeding success. The onset of monsoon rainfall seemed to stimulate initiation of peak breeding activity (Joshi, 1987). Rajagopal and Davidar (2008) assumed that correlation between rainfall and juvenile recruitment is apparent for a few species (Heteropneustes fossilis, Mastacembalus armatus and Mystus vittatus with 5% significance) during the wet season in Kanyakumari. According to them, breeding season of these species was during March to July, in other words during dry season. In case of Ompok pabo also similar result was observed because of low rainfall. Precautions were undertaken to maintain all these parameters as far as possible in the next breeding experiments. That is why; in the year 2010, breeding performance of Ompok pabo was satisfactory. Maximum fertilization rate was increasing up to 85.1% and hatching rate up to 50.1%. [30]

53 The hatching rates were also recorded with similar trend of variation but lower than the fertilization rate in each experiment. Das (2002) reported in Clarias batrachus (magur) that low hatching rates and survival of seeds produced in hatchery can be attributed to several factors such as a) high air and water temperature b) high water ph c) absence of aeration facility d) delay in removal of egg shells and debris, resulting in deterioration of water quality and e) inadequate densities of zooplankton and other live food for the hatchlings. In the present study, many of above factors were found correct after investigation. But delay in removal of egg shells and debris from the rearing tub might be a factor for heavy mortality of hatchlings in the experiments done during 2008 and 2009 year. In spite of above mentioned factors, survival rate was never found below 35%. According to Das (2002), 35% survival rate from spawn to fry is fairly a good percentage for a village level production system, as this stage is regarded as the most crucial in seed production in case of Clarias batrachus. Sahoo et al. (2005) revealed that higher or lower doses of ovatide affected the egg quality, lead to spawning failure or low output of hatchlings. Knud-Hansen et al. (1990) reported 85 to 96% eggs of Clarias batrachus, of which an average of 49.7% successfully hatched. In the present study, hatching rate (between 40.5% and 50.1%) and fertilization rate (between 68.2% and 85.1%) shows the similar trend of breeding success. Water quality for aquaculturists refers to the quality of water that enables successful propagation of the desired organisms. Das (2002) reported that water quality plays an important role in hatching and survival of magur (Clarias batrachus) seed. All the water quality parameters estimated in the present study were more or less suitable for reproductive growth as well as survival of cultivable fishes. Several physico-chemical or biological factors could act as stressors and adversely affect fish growth and reproduction (Iwama et al., 2000). Mukhrjee et al. (2002) managed certain water quality parameters for pond i.e. brooders tank, breeding tank and larval rearing tank during the induced breeding experiments of Ompok pabo. For these three tanks, temperature ( 0 C) for each was estimated as 29 ± 1, 29 ± 1 and 30 ± 1; ph as , and ; DO (ppm) as , and ; alkalinity (ppm) as 130 [31]

54 ± 10, 140 ± 15 and 135 ± 15 respectively. However, in the present study four study systems (brooders pond, breeding pool, incubation system and nursery pond) were taken into consideration. In induced breeding experiment normally the ph and temperature play a vital role for many of the fishes. In Clarias batrachus the optimum ph and water temperature for successful hatching was found to be between 7-8 and C respectively (Mahapatra, 2004). Slight fluctuation of ph and water temperature was observed in the present experiments. The minor fluctuation in diurnal water temperature might not have influenced any of the breeding parameters (Sahoo et al., 2007). The DO level was comparatively higher in breeding pool (10.54 mg l -1 ) and incubation system (10.28 mg l -1 ) than the other systems. It was due to continuous water shower applied for creation of suitable breeding as well as hatching environment. Dwivedi and Reddy (1986) opined that the environmental parameters like temperature, oxygen, ph, water current enhance the fish breeding and hatching and the spray and shower not only increase the dissolved oxygen, but also keep their environment cool and stimulate natural conditions. The maximum free CO 2 value (4.4 mg l -1 ) in the breeding pool resulted due to the heavy shower. But in the other systems, the values fluctuated between the ranges of 2.2 and 3.3 mg l -1. Sarkar et al. (2006) reported free CO 2 value as 2.3 ± 0.5 ppm (mg l -1 ) in brood stock pond and breeding pool which was favorable for breeding of Chitala chitala. However, the other parameters such as alkalinity (75 to 90 mg l -1 ), acidity (2.2 to 6.6 mg l -1 ), hardness (49 to 58 mg l -1 ) and chloride values (7.89 to 8.77 mg l -1 ) for each system were within the suitable ranges for fish production and survival. [32]

55 3.5. EMBRYOLOGICAL AND LARVAL DEVELOPMENT Introduction: Embryonic development is a complex process in which cellular differentiation and proliferation occur simultaneously but at different rate (Hall, 1992). Changes in the pattern of the entire structure of an organ or of specific organ in relation to the environment are decisive for evaluating the developmental pattern of a species (Balon, 1999). The main objective of this whole investigation is to propagate and culture of Ompok pabo in captive condition. In this regard, understanding of every life stage throughout the life cycle is considered necessary. Early life history information is an essential requirement for optimization of mass seed production, culture and management (Khan and Mollah, 1998) which is very much important to optimize larval growth and survival. This information can then be used for the management and culture of the species in any environment. Marimuthu and Haniffa (2007) revealed that embryonic development and larval development besides providing interesting information in itself are imperative and consequential to the successful rearing of larvae for large scale seed production. The observations made after studying fish eggs, embryonic and larval development in fisheries sciences, aquaculture, taxonomy and ecology have been much highlighted (Blaxter, 1974). According to Chakrabarty et al. (2008), the development biology of Ompok pabda is an important aspect which may be considered as base line information for the researchers and fish culturists who are engaged in the seed production of the species. Therefore, the present study has been conducted and provides detailed information about the embryonic and larval development of Ompok pabo Incubation of fertilized eggs: Fertilized eggs were transferred from the breeding hapa to the pre-arranged incubation tub in the laboratory. Eggs were evenly spread on the surface of the tub. Water was sprinkled over the rearing tub by a small shower. To prevent the direct entry of plankton in to the rearing system, a piece of plankton net was fixed at the tip of the of PVC pipe (inlet). For the first five hours water flow was maintained at about 0.5 l/min to keep the eggs circulating surrounding the incubation unit. The plastic tub had an [33]

56 outlet guarded by a fine net. After five hours it was increased up to 1 l/unit to facilitate the removal of unfertilized eggs and to increase oxygen supply to the developing eggs. Gradually the unfertilized eggs were lifted out by a soft brush manually. At a short interval water was disturbed to prevent the overlapping or clumping of eggs on the bottom. After 22 to 24 hours, the hatched larvae were collected from the incubation tub and transferred to separate earthen tub of 40 liter capacity. To investigate the embryological stages, one or two egg was lifted out with the help of feather and placed in a cavity block for microscopic (simple) observation. Photographs were also taken by digital camera for each stage in macro image system Embryonic development: Details time wise embryological events in Ompok pabo are summarized in table The time taken to develop in to different stages was more or less similar with the other Ompok catfishes. However, variations were also noticed in some of the main embryological stages in terms of time taken Nature of egg: Eggs were brownish in color and adhesive in nature. Fertilized eggs were very transparent and had a reddish brown spot on one side and easily recognizable with naked eye. But unfertilized eggs were creamy white in color not transparent. The size of the fertilized eggs ranged from 1.0 to 1.3 mm while the unfertilized eggs of Ompok pabo measured as mm in diameter. Within 30 to 33 minutes after fertilization all the eggs swelled up uniformly with a small perivitelline space Formation of embryo: The first cleavage took place about 36 minutes after fertilization with the formation of blastodisc as a creasentic light area over one end of the massive yolk, which was divided in to two blastomeres. After 10 to 12 minutes the second cleavage (four cell stage) took place and the third cleavage (eight cell stage) followed in another 12 minutes. The fourth cleavage (16 cell stage) was visible in next 8 minutes, followed by the fifth in another 4 to 5 minutes. Thus, the 64 cell stage was observed in 82 minutes after fertilization. The morula stage was attained in 2:06 hours. The [34]

57 blastoderm cells began involution over the yolk in 3:15 hours after fertilization. Eggs were with a small perivitelline space. An advance stage (blastula) was observed in 3:30 hours where a third of egg space covered by the blastoderm cells. Yolk plug stage was in progress in 4:20 hours and found distinct in 5 hours after fertilization. In the 6 hours the yolk mass was completely covered by the blastoderm cells. A thick portion of the embryo was found at one side. This determined the cephalic region of the embryo Differentiation of embryo: Observation made at hours revealed that the embryo became elongated. The rudimentary notochord was found to be laid in the embryo. Elongation of the embryo was complete and it turned the shape of kidney. Embryo was found enlarged in size and more elongated in about 9.00 hours. The cephalic and caudal end had become almost differentiated. In the hours both the ends were found more distinct. The rudiments of optic vesicle were going to be formed. In the hr embryo, an oval area was observed at the base of caudal region which will in later form kupffer s vesicle. The cephalic end became prominent. Caudal end was almost free from the yolk mass. In the next hr, the tail rudiments get separated and optic vesicle fully developed. Embryo was become more developed. Twisting movement of the developing embryo observed which took place in short intervals. The outer vitelline membrane was found gradually decomposed or dissolved at hour. Twisting movement found rapid then earlier at this stage. Yolk mass differentiated in to yolk bulb. The caudal region at this stage was found more active. In hr old embryo, the caudal region became very much elongated. The gut was faintly indicated at the posterior end of the yolk sac. The egg membrane became decomposed and lost its shape. The embryo started active movement within the egg membrane. The eye was found prominent in 19 hours stage. The cephalic region was well formed and became free from yolk mass. The rudiments of maxillary barbels were visible in 20:25 hours. Within hour, frequent whipping motions of the embryo were observed. The egg membrane gradually lost its shape. Finally it broke and the embryos hatched out in 22 hours of incubation after fertilization. The temperature in the incubation unit at the time of hatching was recorded as C. [35]

58 Time after Spawning Table Embryonic development of Ompok pabo Development stage Ontogenic events 0 min Fertilized egg Eggs were adhesive, spherical, transparent and brownish in color. The diameter of the fertilized eggs varied from 1.0 mm-1.3 mm. 36 min 2 cell stage First cleavage 46 to 48 min 4 cell stage Second cleavage 60 min 8 cell stage Third cleavage 1:08 h 16 cell stage Fourth cleavage 1:12-1:13 h 32 cell stage Fifth cleavage 1:22 h 64 cell stage Sixth cleavage 2:06 h Morula stage Blastulation progresses to form a multicellular blastodisc. 3:30 h Blastula stage A third of egg space covered by the blastoderm cells. 5:00 h Yolk plug stage 7:00-8:00 h Kidney shaped embryo 9:00-10:00 h Enlarged embryo 11:00-12:00 h Kupffer s vesicle formed 13:0-14:00 h Optic vesicle developed 15:00-16:00 h Rapid twisting movement Yolk invasion complete and cephalic region gets thicker in size. Elongated embryo with rudimentary notochord. The cephalic and caudal end become almost differentiated. An oval area is observed at the base of caudal region to form kupffer s vesicle. The tail rudiment gets separated and optic vesicle fully developed. Yolk mass differentiated in to yolk bulb. The caudal region at this stage was found more active. 17:00-18:00 h Fully active The egg membrane becomes decomposed and embryo lost its shape. 20:00-21:00 h Just before Embryo with prominent eye with rudiments of hatching maxillary barbels. 22:00 h Hatchling Hatching of embryos starts. [36]

59 PHOTO PLATE: VI Photo 6.1 Early embryonic development of Ompok pabo A. Fertilized eggs B. Unfertilized eggs C. One cell stage (36 mints) D. Two cell stage (48 mints) E. Four cell stage (60 mints) F. Eight cell stage (68 mints) [37]

60 PHOTO PLATE: VI (CONT ) G. Sixteen cell stage (74 mints) H. Sixty four cell stage (82 mints) I. Morula stage (2:06 h) J. Blastoderm involution (3:15 h) K. Yolk plug in progress (4:15 h) L. Six hours old [38]

61 PHOTO PLATE: VI (CONT ) M. Seven hours old N. Eight hours old O. Nine hours old P. Ten hours old Q. Eleven hours old R. Twelve hours old [39]

62 PHOTO PLATE: VI (CONT ) S. Thirteen hours old T. Fourteen hours old U. Sixteen hours old V. Eighteen hours old W. Ninteen hours old X. Twenty hours old [40]