Molluscs are the most important resources among all the seafood items in South-East Asian countries. However, very little information available on nutritional value of molluscs in these regions. In this study, we evaluated the 7 economically important species of molluscs in terms of proximate composition, amino acids profile, fatty acids profile, cholesterol and heavy metal contents in the bivalves (mussels, oysters, clams and cockles) and univalve (snail) collected from freshwater and marine environments of Bangladesh. The results of the proximate analyses revealed that significantly higher amount of crude protein contents were present in marine water oysters, clams and cockles (59.3 AE 0.3 to 75.4 AE 0.2%) than the freshwater mussels and snail (36.9 AE 0.4 to 49.6 AE 0.6%) on dry matter basis. However, carbohydrate contents were significantly higher in freshwater mussels and snail (30.2 AE 0.9 to 57.3 AE 0.2%) compared to the marine water bivalves (8.1 AE 0.4 to 20.2 AE 0.6%). Crude lipid contents were ranged from 2.5 AE 0.2 to 11.2 AE 0.1% and ash from 11.4 AE 0.1 to 16.8 AE 0.6% among the bivalves and snail species. The amino acid contents were comparatively higher in marine water bivalves than their freshwater counterparts. Saturated fatty acid contents were found to be higher in marine water bivalves than the freshwater mollusc species. The results also show that the omega-3 (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) fatty acids were comparatively higher in oysters, clams and cockles in marine water than those in freshwater mussels and snail. However, omega-6 fatty acids like linoleic acid (LA), αlinolenic acid (ALA) and arachidonic acid (ARA) were higher in freshwater mussels and snail than in the marine bivalves. The n-3/n-6 ratio were significantly higher in oysters and cockle species than the other groups of bivalves and snail. The index of atherogenicity and index of thrombogenicity of the mollusc species ranged from 0.74 AE 0.1 to 1.74 AE 0.2 and 0.5 AE 0.1 to 2.6 AE 0.2, respectively. The results show that marine water bivalves contained higher amount of potassium, sodium, iron, chlorine especially oyster species contained significantly higher iodine than the freshwater bivalves and snail. However, freshwater mussels and snail showed significantly higher amount of zinc contents than the marine bivalves. The heavy metal contents such as arsenic, chromium and mercury were absent or present in very tiny amounts among the mollusc species. Significantly higher amount of cholesterol was present in marine bivalves and freshwater snail species than the freshwater mussels. Overall, the results indicate that marine bivalves can be good sources of high quality protein and lipid especially EPA and DHA. On the other hand, freshwater mussels and snails also could be good sources of protein, LA and ARA but scarcity of EPA and DHA.

The present research work was conducted to evaluate the effects of organophosphate insecticide, sumithion on water quality parameters, density of plankton population and histological changes of kidney and liver of the fish, tilapia (Oreochromis niloticus) in aquaculture ponds during July to December 2016. The experiment was conducted with four treatments, each with two replications. Treatment T0 was used as control (no sumithion) and other three treatments with 0.025 ppm (T1), 0.050 ppm (T2) and 0.100 ppm sumithion (T3). The water quality parameters such as dissolved oxygen, free carbon dioxide, pH, total alkalinity, NO3-N and PO4-P fluctuated significantly under four treatments during the experimental period but they were not affected by sumithion application. The phytoplankton densities (×105 cells L-1) was not affected by sumithion. Six genera of phytoplankton populations were found in the experimental ponds. On the other hand, zooplankton population densities (×103 cells L-1) were significantly reduced with increasing doses of sumithion (T2 and T3) in comparison with that of control (T0). Histological changes of kidney were observed after application of sumithion. The renal corpuscle, collecting duct, hematopoietic cells and other cells of the kidney in control (T0) were normal and systematically arranged. Abnormal collecting duct, Intra-cellular space, degenerated renal corpuscle, irregular shaped blood vessel, ruptured membrane large vacuole and necrosis were found in T1, T2 and T3.Normal structure of liver cells such as hepato-pancreas, hepatic cell and blood vessel were observed in T0 (control). Sumithion exposed liver sections showed rupturedhepato-pancreas, necrosis, hemorrhage, intra-cellular space, degenerated hepatopancreas and large vacuole were found in T1, T2 and T3. Therefore, it reveals that sumithion has adverse effects on kidney and liver of the test fish. So, sumithion should not be used indiscriminately in agriculture and aquaculture practices. It may be concluded from the research finding that dissolved oxygen, free carbon dioxide, pH, total alkalinity, PO4-P, NO3-N, phytoplankton and zooplankton values under treatment, T0, are significantly different from treatments T1, T2, and T3 in most cases. Int. J. Agril. Res. Innov. & Tech. 9 (1): 84-95, June, 2019

The experiment was conducted to evaluate the production performance of freshwater mud eel (Monopterus cuchia) with supplementary feed for a period of 5 months in field level. Two ponds were selected for this experiment in Maulovibazar district. Baby cuchia having weight of 50-70 g were stocked in ponds at a stocking density of 10/m2 in filter net. Liming (CaO) was done in all the ponds at rate of 250 kg/ha. A safety shelter for cuchia was developed by installing bamboo root, plastic and bamboo-made hollow pipe, aquatic vegetation and necessary objects in the pond. Different physico-chemical parameters were found to be within the acceptable ranges for M. cuchia culture in all ponds. Supplementary feed composed of fish paste (50%), fish meal (40%), rice bran (5%) and wheat flour (5%) was applied at the rate of 2-3% of body weight. After 5 months of rearing, total production obtained were 28.3±1.09 and 31.9±2.56 kg from pond-1 and pond-2, respectively. The highest production was obtained from pond-2 and lowest production was obtained in pond-1. The net profit gained from pond-1 and pond-2 were tk 2559 and 3211 per decimal, respectively.

The experiment was conducted to determine the effect of population density on growth and production of Tilapia (monosex GIFT tilapia) in monoculture system for a period of 110 days. The experiment was carried out in six earthen ponds, which were situated in the Bangladesh Agricultural University Campus, Mymensingh. The experiment was carried out under three treatments each with two replications. Fish population density was 200 fish per decimal under treatment-I, 400 fish per decimal under treatment-II and 600 fish per decimal under treatment-III. In the ponds supplementary feed of wheat bran and rice bran mixture were used daily at the rate of 46 g, 92 g and 136 g per decimal under treatment-I, II, and III, respectively. The average initial length and weight of tilapia were 4.63 cm and 2.82 g respectively. The ponds were fertilized fortnightly with urea and TSP at the rates of 60 g and 90 g, respectively. During experimental period, the ranges of water temperature (25.82 to 29.80 ºC), transparency (28.00 to 38.00 cm), dissolved oxygen (5.50 to 8.30 mg/L), pH (7.00 to 7.90), total alkalinity (130.00 to 200.00 mg/L), free CO2 (2.00 to 6.00 mg/L), phosphate-phosphorus (1.20 to 2.30 mg/L), and nitrate-nitrogen (3.20 to 4.00 mg/L) were within the productive range and more or less similar in all the ponds under three treatments. There were 25 genera of phytoplankton under five major groups and 10 genera of zooplankton under three major groups in the experimental ponds. Mean survival rate of fish under treatment-I, treatment-II, and treatment-III were 82.75%, 77.12% and 74.33% respectively. The calculated net fish production under treatment-I was 6.75 ton/ha/yr and that of the ponds under treatment-II was 10.26 ton/ha/yr and that of the ponds under treatment-III was 12.15 ton/ha/yr. The net fish production under treatment-II and treatment-III were 152% and 180% higher than that of treatment-I, taking net fish production under treatment-I for 100%. According to profit-cost analysis, the ratios of net profit under treatments I, II, and III were 1:0.44, 1:0.27, and 1:0.09. According to specific growth rate and survival, treatment-I is the best, and according to profit-cost analysis treatment-I (ratio 1:0.44) also the best. So, the population density of 200 fish per decimal (under treatment-I) might be considered the best among the three treatments.

The experiment was conducted to determine the effects of population densities of tilapia (Oreochromis niloticus) on the growth and production of tilapia in monoculture system. Fish population density was 80 fish per decimal under treatment-I, 160 fish per decimal under treatment-II and 320 fish per decimal under treatment-III. In the ponds under three treatments supplementary feed was not used. The average initial length and weight of the fry of tilapia was 4.48 cm and 0.067 g, respectively. The ponds were fertilized fortnightly with urea and TSP at the rates of 60 g, and 90 g per decimal, respectively. Mean survival rates of fish under treatment-I, treatment-II and treatment-III were 91.12%, 82.82% and 66.23%, respectively. The specific growth rates (SGR, % per day) of fish under treatment-I, treatment-II and treatment-III were 5.49%, 4.95% and 4.61%, respectively. The calculated net fish production of the ponds under treatment-I was 2.65 ton ha-1 yr-1 and that of the ponds under treatment-II was 2.55 ton ha-1 yr-1 and that of the ponds under treatment-III was 2.68 ton ha-1 yr-1. The net fish production under treatment-I and treatment-III were 2.65 ton ha-1 yr-1 and 2.68 ton ha-1 yr-1 higher than that of treatment-II, taking net fish production under treatment-I for 100%. According to survival rates and specific growth rates treatment-I is the best. So, the population density of 80 fish per decimal (under treatment-I) might be considered the best among the three treatments. Int. J. Agril. Res. Innov. Tech. 9(2): 76-83, December 2019