Key words: Zooplankton, abundance, genus composition, Mouri river.

Bangladesh J. Zool. 38(2): 243-252, 2010 ASSESSMENT OF THE ABUNDANCE AND GENUS COMPOSITION OF ZOOPLANKTON OF THE MOURI RIVER, KHULNA Md. Lifat Rahi* and Wasim Sabbir Fisheries and Marine Resource Technology Discipline, Khulna University, Khulna-9208, Bangladesh Abstract: The present study was aimed at the identification and assessment of zooplankton abundance in the Mouri River, Khulna, Bangladesh for a period of six months (February- July, 2008). Water samples were collected once a week from six different stations of the river. In total four different groups and 24 different genera of zooplankton were identified where copepods were the dominant group throughout the river constituting 33-83.33% of total zooplankton biomass at different stations. The maximum abundance of zooplankton was 1230 individuals/l at station-vi and minimum 200 individuals/l at station-ii. Significant correlation was observed between several water quality parameters and zooplankton abundance. Water temperature, transparency, free CO2, ph, dissolved O2, alkalinity and hardness showed positive correlation with plankton abundance whereas sulphate, phosphate, calcium, nitrate and magnesium showed negative correlation. However, the results of this experiment confirmed the polluted water of the river. mvi-ms ct Lyjbvq gqdi b`xi RyIc vsub mbv³kiy Ges cwigvb wby qi Rb 6 gvm e vcx ez gvb M elyv cwipvwjz nq b`xi QqwU wewfbœ vb ( ókb) n Z cvwbi bgybv msmön Kiv nq gvu Pvi cökvi wewfbœ MÖ ci Aax b 24wU MY mbv³ Kiv nq hlv b K c cvwv MÖ ci cwigvb wqj me vwak (33-83.33%) 4bs ók b RyIc vsu bi cövßzv wqj me vwak (1230/wjt) Ges 2bs ók b me wbgœ (200/wjt) cvwbi wewfbœ Yvejxi mv _ RyIc vsu bi cövc Zvi m úk cwijw Z nq cvwbi ZvcgvÎv, ^ QZv, LiZv, gy³ Kve bwvb A vbw, G vjk vwjwbwu I `ªwefyZ Aw R bi mv _ abvz K m úk Ges mvj du, dm du, K vjwmqvg I bvb UªU Gi mv _ FYvZ K m úk `Lv hvq hvb nvk, GB M elyvi djvdj b`xi mvgwmök `~wlz Ae vib Bw½Z `q Key words: Zooplankton, abundance, genus composition, Mouri river. INTRODUCTION Zooplankton is an essential component of aquatic biodiversity which occupies an intermediary position between autotrophs and carnivores and forms an important link in aquatic food web as it is in the second trophic level as primary consumer and as contributor to the next trophic level. Nature is the nourisher of all kinds of life system on the earth by providing proper environment to the living beings (Azher et al. 2006). Zooplankton constitutes an important food item of many omnivorous and carnivorous fishes (Bhuiyan 1988) and provides the necessary amount of protein for rapid growth and especially that of the gonad (Ballard and Myers 2000). The larvae of white fish (Mullet) feed

244 Rahi and Sabbir *Corresponding author. E-mail: lifatrahi@gmail.com mostly on zooplankton, contribute about 82% of the food item of Anabas testudineus (Ali et al. 1985), 32% of Notopterus notopterus (Das and Das 1980), main food item of Xenentodon cancila (Islam et al. 2007). The qualitative and quantitative values of plankton in a body of water form the basic link in the food chain of fishes (Bhuiyan and Nessa 1998a, Islam et al. 2008). Hence, those who interpret the zoogeography and migratory strategies of predators at higher trophic levels need to understand the distribution and abundance patterns of zooplankton (Murphy et al. 1998). But, a total list of zooplankton from diverse habitats of Bangladesh is not yet complete (Roy et al. 2008). Plankton is recognized worldwide as bio-indicator organisms in the aquatic environment and increase productivity of water (Yakubu et al. 2000, Abowei et al. 2008). On the other hand, many members of zooplankton community act as the indicator of aquatic pollution (Osore 2004). Plankton blooms may indicate the presence of mineral ions, populations of planktonic ciliates, oxygen-depletion and polluted water (Boyd et al. 2000). In any aquatic ecosystem the zooplankters not only take part in transferring food from primary to secondary level but also switch over conversion of detritus matter into edible animal food. The distribution of zooplankton has long been to be heterogeneous; spatial heterogenisity is common feature in all ecosystems and is the result of many interacting physical and biological process (Pinel-Alloul 1995, Gaston 2000). The study of freshwater micro-fauna especially zooplankton, even of a particular area is extensive and complicated due to environmental, physical, geographical and chemical variations involving ecological, extrinsic and intrinsic factors (Vijaykumar 2009). The seasonal fluctuations of the zooplankton population are well known phenomenon and zooplankton exhibits a bimodal oscillation with a spring and autumn in temperate lakes and reservoirs (Bhuiyan and Nessa 1998b, Wetzel 2001). This fluctuation is greatly influenced by the variations in the temperature along with many factors including rainfall variation, depth of water body, siltation and other chemical factors (Bhaumik et al. 2006). The Mouri river flows through the North West side of the Khulna city and separates the Domuria thana from Khulna city. The river is about 9.5 km long and falls into the Rupsha river near Badamtala, Khulna. From the very beginning of the Khulna city modernization for the civilian this river is used as the dumping ground of various municipal, industrials and domestic wastes. Under the Khulna Development project the river is controlled by established sluice gate at the opening mouth near Badamtala in 1983 to recover the lands which were under tidal action. Since then the river acts as the reservoir of wastes produced from various sources in Khulna city. There are about 18 big

Assessment of the abundance and genus composition of zooplankton 245 and small canals and drains that drain out the effluents and waste products from the whole Khulna city. The total system makes the river polluted day by day. But the river still acts as a source of fish production and many people use this river water for their domestic purposes. However, very little is known about the zooplankton fauna of Bangladesh as published information on zooplankton composition is comparatively lacking and particularly no work has been done in the Mouri river. OBJECTIVES The objective of the present study was to assess the abundance of different zooplankton genera and also to determine some physico-chemical parameters of the river. MATERIAL AND METHDS Selection of the study area: Six different stations were selected at 1.5 km interval. The stations were Rayar Mohal (Station-I), Shashanghat (Station-II), Gollamari bridge (Station-III), near Moulovir Dargah (station-iv), Nirala grave yard (Station-V) and Ten gate (Station-VI). Sampling: Samples were collected from the six different stations at morning (8-9 am) using plankton net having 90µm mesh size. Zooplankton samples were then preserved with borax buffered formalin at a rate of 1.5ml per 250 ml samples. Samples were preserved in plastic bottles. Zooplankton identification and counting: Zooplankton identification was performed according to the literature of Davis (1956). The Sedgwick-Rafter (S-R) cell (50 mm long, 20 mm wide and one mm deep) was used for zooplankton counting. At first one ml of sample was taken in S-R cell which was kept stable for 15 minutes to allow the zooplankters to settle down. Then the plankters on the bottom of the S-R cell were counted under a microscope. The S-R cell is equally divided into 1000 fields, each having a volume of 0.001 ml. Zooplankton counting was then performed by using the well established formula: No /ml = C x 1000 mm3 L xd x W x S Where, C = Number of organisms counted; L = length of each strip (S-R cell) in mm; W = Width of each strip (S-R) cell in mm; D = depth of each strip (S-R cell) in mm; and S = number of strips counted. Water quality parameters: Water temperature, ph, transparency were measured by using mercury thermometer, ph meter, secchi-disc, respectively. Dissolved oxygen, free CO 2, alkalinity and hardness were measured by

246 Rahi and Sabbir titrimetric method (Greenberg et al. 1992). Sulfate, Phosphate, calcium and magnesium were determined according to the methods of Romesh and Anbu (1996). Nitrate was determined by colorimetric method. RESULTS AND DISCUSSION Genus composition of zooplankton: The results of the zooplankton genus composition are presented in Table 1. In total 24 different zooplankton genera under four different groups (order) were identified. Rotifer consisted of the highest number of genera (9 genera) whereas copepods, ostracods and cladocerans comprised of seven, five and three genera, respectively. In station-i, two groups of zooplankton, namely Ostracoda and Cladocera were absent whereas Table 1. Group and genus composition of zooplankton at different stations of the Mouri river. Different Stations Group and Genus Station-I Station-II Station-III Station-IV Station-V Station-VI 1. Rotifera Lapadella P - - - - - Notholca P - - P - - Platyias P - - - - - Canuella - P P - - - Filinia P - P - - - Hyocryptus - - - P - - Lecane - - - - P P Calurella - - - - P P Brachionus - - - - P P 2. Copepoda Tisba P P P P P P Cyclops P - P - - - Diaptomus P - P - - - Mesocyclops - P - - - - Eucyclops - - - P - - Metis - - - - P P Harpacticoid - - - - P P 3. Ostracoda Cypris - - P - - P Cyprinotus - - - - - P Cyclocypris - - - P - - Cyprinida - P P P - - Stenocypris - - P - - - 4. Cladocera Sida - P P P P - Daphnia - - P - - - Moina - - - P P - P = Present, - = Absent.

Assessment of the abundance and genus composition of zooplankton 247 only one group was absent in Station-V (Ostracoda) and in Station-VI (Cladocera). The most frequently observed genus was Tisba and was found in all the stations. The lowest observed genera were Hyocryptus, Lapadella, Platyias, Mesocyclops, Eucyclops, Cyprinotus, Cyclocypris, Stenocypris and Daphnia. Roy et al. (2008) identified 21 genera of zooplankton from a managed pond based on one year investigation of which three genera belonged to Cladocera (19.22%), five to Copepoda (36.13%), 12 to Rotifera (44.59%) and one to Ostracoda (0.06%). Islam et al. (2008) identified six genera of zooplankton under copepods, rotifers, cladocerans and ostracods in a monoculture system pond and seven genera under the same groups in a polyculture system pond. Azher et al. (2006) identified 15 genera of zooplankton under Cladocera, Copepoda and Rotifera from two beels of Bangladesh. Osore et al. (2004) reported 27 major taxa of zooplankton in a Kenyan creek. Abowei et al. (2008) identified six taxonomic groups of zooplankton from the Sombreiro river of Nigeria. In addition, Hasan (2004) and Rahaman (2004) recorded 11 and 15 genera of zooplankton from different water bodies of Bangladesh. Thus, the results of the present study showed a comparatively diverse composition of zooplankton genera in the Mouri river. Zooplankton abundance: The results of the zooplankton abundance (groupwise) and percentage composition are presented in Table 2. The total zooplankton abundance at different stations has been shown in Fig. 1. The highest zooplankton abundance was observed as 1230 individuals/l at station- VI and the lowest 200 individuals/l at station-ii. Zooplankton abundance was Table 2. Group wise distribution and percentage composition of zooplankton at different stations in the Mouri river. Station No/L Zooplankton Group Copepoda Rotifera Cladocera Ostracoda Total % Of total No/L % Of total No/L % Of total No/L % Of total I 125 60.1 80 39.9 - - - - 205 II 140 70 - - 40 20 20 10 200 III 70 33 90 42 20 9 30 14 210 IV 240 41.37 140 25.71 80 13.71 40 6.0 580 V 630 64.94 210 21.64 130 13.40 - - 970 VI 1025 83.33 125 10.16 - - 80 6.5 1230 observed to be almost similar at stations-i, II and III as 205, 200 and 210 individuals/l, respectively. Zooplankton abundance was moderate at stations-iv and V as 580 and 970 individuals/l. Copepods were the most dominant group in the river throughout the study period constituting 33-83.33% of the total zooplankton biomass. Ostracods were the least abundant group in the river

248 Rahi and Sabbir constituting only 6-14% of the total zooplankton biomass. The remaining two groups of zooplankton cladocerans and rotifers were moderately abundant in the river ranging from 9% to 42% of total zooplankton population. The pollution indicator groups Rotifera and Copepoda were comparatively higher in station I to III than the other stations indicating a comparatively higher amount of dumping in these areas. The population density was much higher in the Station-V and VI due to lower load of organic pollution and station-iv showed an intermediate position indicating medium level of pollution. Lower zooplankton abundance was Zooplankton abundance (Indv./l) 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0 1 2 3 4 5 6 Stations Stations Fig. 1. Total Zooplankton abundance at different stations in the Mouri river. observed at stations-i, II and III due to higher dumping rate in these areas. Thus, total zooplankton abundance is comparatively low in this river because of its polluted water. Azher et al. (2006) reported zooplankton abundance as 611-1722 cells/l in a beel of Bangladesh where copepods were the dominant group (40-47% of total zooplankton). Zooplankton abundance was observed as 132-1054 units/l in two beels of West Bengal, India where the abundance of copepods was the minimum as 7.69-15.30% of total zooplankton biomass and maximum for rotifer as 52.02-70.97% (Bhaumik et al. 2006). Osore et al. (2004) reported the highest zooplankton abundance as 1961-2856 individuals/m 3 during the dry season (Feb. to Mar.) and the lowest as 77-352 individuals/m 3 during the wet season (May-June). Patra and Azadi (1987) and Khan et al. (1990) reported that copepods were the dominant group throughout the Halda river. Khan et al. (1990) also reported that the rotifers were the second dominant group which supports the present experiment.

Assessment of the abundance and genus composition of zooplankton 249 Zooplankton abundance in relation to some physico-chemical parameters: The measured physico-chemical parameters of the river differed from place to place and significant correlation was found between zooplankton abundance and physico-chemical parameters (Table 3). Positive correlation was found between zooplankton abundance and temperature (r = 0.867), transparency (r = 0.823), water ph (r = 0.447), DO (r = 0.667), free CO 2 (r = 0.509), alkalinity (r = 0.479) hardness (r = 0.479). Negative correlation was found between zooplankton abundance and sulfate (r = -0.535), phosphate (r = -0.635), nitrate (r = -0.539), calcium (r = -0.806), magnesium (r = -0.879). Total zooplankton abundance was very low in the areas of high dumping rate where the physico-chemical parameters showed a sharp deviation from the optimum levels. Different environmental Table 3. Correlation between zooplankton abundance and different water quality parameters in the Mouri river. Parameters Zooplankton Group Copepods Rotifers Ostracodans Cladocerans Total r r r r r Temperature 0.591133 0.947753 0.686084-0.63073 0.867563 Transparency -0.17525 0.675172 0.75779-0.64539 0.823446 Water ph 0.174523 0.535447 0.337021-0.61842 0.446924 Dissolved O2 0.665798 0.896255 0.45404-0.52026 0.667351 Free CO2-0.36339 0.505866 0.596924-0.49259 0.508812 Alkalinity 0.016728 0.519124 0.20502-0.02872 0.479449 Hardness -0.21304 0.422269 0.233231-0.03764 0.479449 Sulfate 0.359034-0.21774-0.75444 0.40966-0.53544 Phosphate 0.380142-0.3155-0.75667 0.334761-0.63498 Nitrate -0.91954-0.77132-0.4342 0.633912-0.53905 Calcium -0.44904-0.83883-0.58378 0.422189-0.80648 Magnesium -0.60029-0.90564-0.84881 0.805533-0.87902 factors that determine the characters of water have great importance upon the growth and abundance of zooplankton. Islam (2007) reported a significant correlation between zooplankton abundance and physico-chemical conditions of water. Significant positive and negative correlation was also observed between zooplankton abundance and water quality parameters in several rivers of the Sundarbans of Bangladesh (Alam and Kabir 2003) which supports the present study. Roy (1955), Nikolosky (1963) and Jhingran (1985) also found significant correlation between the abundance of plankton population and physicochemical parameters of water body. Among several factors, temperature seems to exhibit the greatest influence on the periodicity of zooplankton (Raybaud 2008). Water temperature between 10 and 29 o C is suitable for zooplankton development (Kaushik et al. 1992). The greater deviation and fluctuation of water quality parameters at different stations were observed due to the

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