STUDIES ON SOME ASPECTS OF FEEDING BIOLOGY OF MACROGNATHUS ARAL (BLOCH AND SCHNEIDER, 1801) AN IMPORTANT FRESHWATER ORNAMENTAL FISH

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1 STUDIES ON SOME ASPECTS OF FEEDING BIOLOGY OF MACROGNATHUS ARAL (BLOCH AND SCHNEIDER, 181) AN IMPORTANT FRESHWATER ORNAMENTAL FISH * Dibyendu Dutta and Samir Banerjee Department of Zoology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata-719, West Bengal, India *Author for Correspondence ABSTRACT The one stripe spiny eel Macrognathus aral (Bloch and Schneider, 181) has been gaining importance not only as a food fish but also as an ornamental fish due to its exquisite coloration and body shape. The present study has been conducted in order to obtain information on the food and feeding habit of this. Relative gut length, gastrosomatic index, gut fullness and gut content analysis have been studied. Based on the obtained results, Macrognathus aral can be considered as a carnivorous fish. Feeding intensity was high in post spawning stages and relatively low in specimens with ripe gonads (mostly females). Insect and zooplanktons comprised the major part of the feeding items. Key Words: Macrognathus Aral, Relative Gut Length, Gastro-Somatic Index, Feeding Intensity, Gut Content Analysis and Index of Pre-Ponderance INTRODUCTION Macrognathus aral (Bloch and Schneider) belongs to family Mastacembelidae.It inhabits both running and stagnant water of plains and estuaries and usually found in canals, streams, beels, ponds and flooded paddy fields. The is distributed to India, Pakistan, Bangladesh, Srilanka, Myanmar and Nepal (Talwar and Jhingran, 1991). It has a long and eel-like body type with a long fleshy snout and a rounded caudal fin that is separated from dorsal and anal fins. In live condition, body color is brownish to yellowish ventrally and presence of two distinct long dark bands on either side of body. There are 3-11 ocelli (false eye spots) at the base of dorsal fin.the Macrognathus aral (Bloch and Schneider) is commonly referred to as the peacock eel and is in high demand as an ornamental fish in the export market due to its eye catching body shape, brilliant coloration and playful behavior. The IUCN red list enlists this fish in the least concern category while as per Conservation Assessment and Management Plan (CAMP) Report (1998) it is included under Lower Risk near threatened (LRnt-category) in India. Studies on food and feeding habit of fishes have manifold importance on fishery biology. In order to accomplish a well planned scientific management of a fish, it is necessary to obtain knowledge about its biological aspects, in which food and feeding habits comprise an important segment (Sarkar and Deepak, 29). Studies associated to feeding of fishes in their natural environments are of major importance for the management of their fishery and also for the environment (Al-Kahem et al., 1988, 199). This also plays a role in understanding the function of fish in environments and its relation with other of fish inhabiting in the same environment. There have been some studies carried out on different biological aspects of Mastacembelidae. Swarup et al., (1972) studied on sexual dimorphism of M. pancalus. Karim and Hossain (1972) investigated the general biology of M. pancalus (Ham.) in artificial ponds and also studied the sexual maturity and fecundity. Kocetov (1992) reported on few aspects of reproductive biology of spiny eels. Narejo et al., (22) studied on the ova diameter, gonadosomatic index, and fecundity of Mastacembalus armatus in Bangladesh. Serajuudin and Ali (25) described the feeding habits of Macrognathus pancalus. Chavan et al., (26) made an effort on the conservation of spiny eel, Mastacembalus armatus. Suresh et al., (26) carried out their study on certain aspects of biology and fisheries of M. pancalus from Ganga river system. Serajuddin and Mustafa (1994) and Serajuudin et al., (1998) investigated the food and feeding habits of Mastacembelus armatus. Rahman and Miah (29) conducted a study on fecundity of Mastacembelus pancalus. However, except for the work of Biswas and Abujam (211), no such significant work on the biological aspects of Macrognathus aral has not yet been carried out in west Bengal. Hence, the present study was aimed at investigating the food and feeding habit of Macrognathus aral. MATERIALS AND METHODS Monthly samples of Macrognathus aral (Bloch and Schneider) were obtained for August, 21 to December, from Ballir beel located in north 24 parganas ( N/ ), West Bengal. A total of 52 specimens were collected during the study period for the studying certain aspects of feeding biology. The time of collection 3

2 Mean relative gut length Ind. J. Sci. Res. and Tech (4):3-39/Dutta & Banerjee was set during the early hours of the morning. After collection, specimens were immediately transferred in ice box and brought to laboratory. Total length of each individual specimen was measured to the nearest of.1 cm using a standard measuring scale and total weight was measured to the nearest of.1 gm using an electronic balance (Sartorius, Model No. BT 223S). Guts of the specimens were carefully dissected out and total length and total weight of gut was recorded. Gastro-somatic index (GaSI) was determined by the following formula, GaSI = wx1/w (Desai, 197) Where, GaSI = gastro-somatic index; w = weight of gut; W = total weight of fish. Monthly Fullness Index (FI) was calculated according to the following formula- FI = Number of gut with same degree of fullness x 1/ Total number of gut examined. (Lebedev, 1946) Relative gut length (RLG) was determined using the formula given below, RLG = l/l (Al-Hussainy, 1949) Where, RLG = relative gut length; l = length of gut; L = total length of the fish. Gut Content Analysis was done following two methods: Occurrence (Hynes, 195) and Points Method (Pillay, 1953). To find out the prevailing food items, Index of Preponderance (IP) was calculated by the following formula IP = V1O1 x 1 / ΣV1O1 Natarajan and Jhingran (1961) Where, V1 = Volume of the particular food item; O1 = Occurrence of the particular food item; IP = Index of Preponderance. Food items present in the gut content have been identified at genus level following standard keys (Philipose, 196; Jana, 1973; Battish, 1992; Sharma, 1999; Venkataraman, 1999; Khan, 23; Bilgrami and Saha, 24). RESULT Study of relative gut length The values of relative gut length index (RLG) were calculated independently for four different size groups [Group I: (1 15 mm); Group II: (151 2 mm); Group III: (21 25 mm); Group IV: (251 3 mm)] following the method of Al-Hussaini (1949) (Fig: 1A). The relative gut length in the total size range of this, including both juveniles and adults varied between (S.E..5). The relationship between gut length and total body length can be expressed by the following regression equation:- Log gut length = Log total length ( r =.829, P<.1) Study of gastro somatic index Mean monthly values of gastro somatic index (GaSI) for female, male and juvenile fishes were determined separately (Fig: 1B-D). In case of Macrognathus aral (Bloch and Schneider) females GaSI reaches its peak value in October and becomes lowest in June. As for males, highest GaSI value is observed in May and lowest in August.GaSI value of juveniles reaches its peak in August and lowest values are observed in December Group I (1-15) Group II (151-2) Group III (21-25) Group IV (251-3) Size groups (mm) Figure 1A: Variation in RLG between different size groups of Macrognathus aral Study of feeding intensity Feeding intensity of both male and female fishes were studied based on observations of gut fullness. Gut fullness was categorized into three main types, empty; semi full and full guts. In case of males highest percentage of fishes with full guts was observed from April to May where as in females it was August to October (Fig. 1E-F). 31

3 Mean Gastro-somatic index Mean Gastro-somatic index Mean Gastro-somatic index Ind. J. Sci. Res. and Tech (4):3-39/Dutta & Banerjee Aug-1 Sep-1 Oct-1 Nov-1 Aug-1 Sep-1 Aug-1 Sep-1 32 Dec-1 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Figure1B: Annual variation in gastro somatic index of Macrognathus aral female Oct-1 Nov-1 Dec-1 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Figure1C: Annual variation in gastro somatic index of Macrognathus aral male Oct-1 Nov-1 Dec-1 Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Figure1D: Annual variation in gastro somatic index of Macrognathus aral juvenile Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Analysis of gut content Feeding items found in the gut content of Macrognathus aral (Bloch and Schneider) have been categorized into eight classes namely Annelida, Copepoda, Cladocera, Rotifera, insect, insect body parts, sand and mud and unidentified.

4 Percentage frequency Percentage frequency Ind. J. Sci. Res. and Tech (4):3-39/Dutta & Banerjee Jan-11 Feb Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Empty guts Semifull guts Full guts Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Figure1E: Annual variation in feeding intensity of Macrognathus aral male Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Empty guts Semifull guts Full guts Figure1F: Annual variation in feeding intensity of Macrognathus aral female Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Gut content analysis was performed separately for each of the four size groups throughout the year following occurrence method and point s method (Table: 1A-H). Index of preponderance was determined for all size groups to estimate the dominant food items (Table: 1I-L). Insect were found to be the most abundant food group in all size groups. Next to it were zooplanktons belonging to Copepoda, Cladocera and Rotifera. Table 1A: Proportions of different feeding items of Macrognathus aral size group I [ Occurrence method] Pre 2.47± ± ± ± ± ± ± Monsoon 1.2± ± ± ± ± ± ± ± ± ± ± ± ± ±2.66 Pre 2.33± ± ± ± ± ± ±3.52 Monsoon 1.98± ± ± ± ± ± ± ± ± ± ± ± ± ±2.65 Table 1B:Proportions of different feeding items of Macrognathus aral size group I [Points method] Pre 1.98± ± ± ± ± ± ± Monsoon 1.97± ± ± ± ± ± ± ± ± ± ± ± ± ±3.55 Pre 1.75± ± ± ± ± ± ±3.12 Monsoon 1.64± ± ± ± ± ± ± ± ± ± ± ± ± ±3.5 33

5 Table 1C: Proportions of different feeding items of Macrognathus aral size group II [ Occurrence method] Pre 3.15± ± ± ± ± ± ± Monsoon 2.41± ± ± ± ± ± ± ± ± ± ± ± ± ±2.29 Pre 2.65± ± ± ± ± ± ±2.11 Monsoon 1.78± ± ± ± ± ± ± ± ± ± ± ±1.86 Table 1D: Proportions of different feeding items of Macrognathus aral size group II [Points method] Pre 2.25± ± ± ± ± ± ±3.52 Monsoon 2.17± ± ± ± ± ± ± ± ± ± ± ± ± ±3.32 Pre 2.1± ± ± ± ± ± ±2.4 Monsoon 1.8± ± ± ± ± ± ± ± ± ± ± ± ± ±2.11 Table 1E: Proportions of different feeding items of Macrognathus aral size group III[ Occurrence method] Insect body parts Pre 1.55± ± ± ± ± ± ± ± Monsoon 3.2± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±2.2 Pre 1.62± ± ± ± ± ± ± ±2.65 Monsoon 2.3± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±1.98 Table 1F: Proportions of different feeding items of Macrognathus aral size group III[Points method] Insect body parts Pre 1.88± ± ± ± ± ± ± ± Monsoon 1.76± ± ± ± ± ± ± ± ±.9 9.1± ± ± ± ± ± ±2.7 Pre 1.58± ± ± ± ± ± ± ±1.78 Monsoon 1.77± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±2.54 Table 1G: Proportions of different feeding items of Macrognathus aral size group IV [ Occurrence method] Insect body parts Pre 1.81± ± ± ± ± ± ± ± Monsoon 1.98± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±3.42 Pre 1.59± ± ± ± ± ± ± ±2.5 Monsoon 1.84± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

6 Table 1H: Proportions of different feeding items of Macrognathus aral size group IV [Points method] Insect body parts Pre 1.73± ± ± ± ± ± ± ± Monsoon 1.69± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±3.73 Pre 1.78± ± ± ± ± ± ± ±1.88 Monsoon 1.51± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±1.76 Table 1I: Index of preponderance (IP) of different food items present in gut content of Macrognathus aral size group I Year Food items. occurrence (O) volume (V) V x O IP Grade Annelida VI Copepoda IV Cladocera III Insect I 211 Rotifera IV Sand,mud V II Annelida VII Copepoda IV Cladocera III Insect I Rotifera V Sand,mud VI II Table 1J: Index of preponderance (IP) of different food items present in gut content of Macrognathus aral size group II Year Food items. occurrence (O) volume (V) V x O IP Grade Annelida VII Copepoda IV Cladocera III Insect I 211 Rotifera V Sand,mud VI II Annelida VII Copepoda IV Cladocera III Insect I Rotifera V Sand,mud VI II 35

7 Table 1K: Index of preponderance (IP) of different food items present in gut content of Macrognathus aral size group III Year Food items. occurrence (O) volume (V) V x O IP Grade Annelida VIII Copepoda V Cladocera VI Insect I 211 Insect body parts III Rotifera IV Sand,mud VII II Annelida VIII Copepoda IV Cladocera VI Insect I Insect body parts III Rotifera V Sand,mud VII II Table 1L: Index of preponderance (IP) of different food items present in gut content of Macrognathus aral size group IV Year Food items. occurrence (O) volume (V) V x O IP Grade Annelida VIII Copepoda VII Cladocera VI Insect I 211 Insect body parts III Rotifera IV Sand,mud V II Annelida VIII Copepoda VI Cladocera VII Insect I Insect body parts III Rotifera V Sand,mud IV II Identification of food organisms Among the insect, damselfly (Family-Coenagrionidae), dragonfly (Family- Libellulidae), Dipteran (Chaoborus sp. Tanypus sp., Chironomus sp.) were very frequent. Among Copepoda, Macrocyclops spp., Eucyclops spp., Diaptomus spp. and among Cladocera, Daphnia spp, Ceriodaphnia spp, Diaphanosoma spp., Moina spp. were very common. Brachionus spp., Filinia spp., Keratella spp.,lecane spp. were the frequently observed Rotifers during gut content analysis. Among Annelida, Tubifex sp., Branchiura sp., Lumbriculus sp. were observed in the diet. DISCUSSION The work of Al-Hussaini (1947) determined the RLG values for carnivorous (.5-2.4), omnivorous ( ) and herbivorous (3.7-6.) fish. Later on Das and Moitra (1956 a, b, c 1958and 1963) also mentioned about high RLG values ( ) in herbivorous fishes while carnivorous fishes showed very low RLG values (.4-.8). Das and Nath (1965) also indicated that RLG values ( ) in omnivorous fishes tend to be lower than herbivorous ones but greater than that of the carnivorous fishes. Therefore the observations of the present study indicate a carnivorous mode of feeding in Macrognathus aral (Bloch and Schneider). The absence of significant difference in relative gut length index of juveniles and adult specimens can be interpreted as a sign of that growth does not involve any noteworthy change in the basically carnivorous mode of feeding of this fish (Fig. 1A). 36

8 The declining trend in feeding activity of the females from March to June corresponds to their breeding season. Previous workers have mentioned similar type of observations in different fish (Jhingaran, 1961; Desai, 197; Bhatnagar and Karamchandani, 1979; Fatima and Khan, 1993; Mitra et al., 26; Gandotra et al., 27; Sarkar and Deepak, 29; Mondal and Kaviraj, 21; Kanwal and Pathani, ). GaSI value in females starts to rise from august after the breeding season is over and after reaching the peak in October a gradual decrease begins (Fig:1B). This decrease in GaSI value occurring way ahead of the breeding season can be explained by the impact of other factors such as non availability of food items or abiotic factors like temperature and turbidity (Abbas, 21). Feeding intensity of both male and female fishes were studied based on observations of gut fullness. Gut fullness was categorized into three main types, empty; semi full and full guts. In case of males highest percentage of fishes with full guts was observed from April to May where as in females it was August to October. Presence of semi full guts all through the year suggests that feeding was continuous even during the spawning seasons. Khan et al., (1988) and Serajuddin et al., (1998) reported similar observations in Mystus nemurus and Mastacembelus armatus respectively. Full guts was absent in case of females from April to June, possibly because of the development of the ovaries which almost occupies almost ¾ th of the entire abdominal cavity. Presence of empty guts in both male and females all round the year also suggests inadequate availability of food in their natural habitat. Fullness indices determined for Macrognathus aral (Bloch and Schneider) males are 16.69%, 63.84% and 19.47% and in females are 23.83%, 66.1%and 1.6% for empty, semi full and full guts respectively. The study of preponderance index of Macrognathus aral reveals the presence of high percentage of insect, insect body parts, zooplankton and other micro invertebrate fauna in its diet confirming its carnivorous mode of feeding. Differences in the prevalence of different feeding items can be due to their differential availability in the habitat where the fish population under present study lived at a particular time. According to Desai (1992) food and feeding behavior of fish diverge as per availability of food, depending on the ecology of the environment. Suresh (26) found similar results while studying a closely related, Macrognathus pancalus. CONCLUSION The diet composition was almost similar for all size groups showing the absence of any major change in food preference with age and growth. The presence of conspicuous amount of sand and mud in gut content suggests that Macrognathus aral is a bottom feeder. Relative gut length values gut content analysis and study of preponderance index for four different size groups of Macrognathus aral strongly suggests that this exhibits a carnivorous mode of feeding. Insect and zooplanktons were the most preferred food items in all four size groups of Macrognathus aral. Further research is required on commercial food preference and feeding strategies for conservation and successful culture of this. ACKNOWLEDGEMENT Authors are grateful to the Head, Department of Zoology, University of Calcutta for providing the lab facilities for the research work. The financial support of the University Grants Commission (UGC) for this research work is gratefully acknowledged. REFERENCES Abbas A (21). Food and feeding habits of freshwater catfish,(bleeker) Eutropiichthys vacha. Indian Journal of Scientific Research, 1(2) Al-Hussaini AH (1949). On the functional morphology of the alimentary tract of some fish in relation to difference in their feeding habits: Anatomy and histology. Q. J. Micr. Sci., Al-Kahem HF, Al-Akei AS, Shamsi MJK & Ahmed Z (1988). Food selection of various size groups of the Cyprinid fish, Cyprinion mhalensis Al-Kahem and Behnke, 1983 from Saudi Arabia. ArabGulf J. Scient. Res. Agric. Biol. Sci., B6 (3): Al-Kahem HF, Al-Akei AS, Shamsi MJK, Ahmed Z & Al-Shawa YR (199). Food selectivity of an Arabian Peninsula's Cyprinid fish, Cyprinion acinaces. Journal of King Saud University, Battish SK (1992). Freshwater zooplankton of India. Oxford and IBH Publishing Company, New Delhi 233. Biswas SP & Singh ASK (211). Studies on the reproductive biology of spiny eel, Macrognathus aral from upper Assam. Journal of Environmental Biology, Bhatnagar GK & Karamchandani SJ (197). Food and feeding habit of Labeo fimbriatus (Bloch) in river Narbada near Hosangabad (M.P.) Journal of Inland Fisheries Society of India, Bilgrami KS & Saha LC (24). A Text Book of Algae. CBS Publishers and Distributors

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