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Objective: This study was carried out to estimate the sex ratio, maturity size, gonadosomatic index (GSI), and peak breeding season of mud crabs. Materials and Methods: Samples were collected randomly from the estuary and river of the study area. Sampling was carried out monthly from April to September at every full moon during one high tide. A total number of 240 specimens were sampled, where 53 individuals were hermaphrodite. The crabs were shifted alive to the biology and histology lab for detailed biological study. Sex was determined. Male and female sex ratio and breeding season were also investigated. Results: The male:female ratio was 1:0.96 and the ovarian development was categorized into five stages based on internal observations, viz. immature (stage I), underdeveloped (stage II), early developed (stage III), late developed (stage IV), and mature (stage V). The maturity percentages were 37%, 19%, 13%, 11%, and 20%, respectively. 50% maturation was estimated at 82.36 mm internal carapace width (ICW). The highest mean GSI value was 7.97 ± 3.03. The mature stage was found in all the working periods. This shows that females have activated ovaries in all the working months, and the species are continuous breeders. A higher frequency of vitellogenic ovary and higher GSI value were found in September. The maximum GSI value was found in the size group 70–79 mm. Conclusion: The study shows that the capture from the wild sources of mud crabs without any regulation can threaten the population structure. The capture of female mud crabs should be more than 82.36 mm ICW, which will help conserve and protect young crabs.

Biofloc technology (BFT) is nowadays considered as eco-friendly approach being used for fish and shellfish production. The present investigation aimed at comparing water quality, as well as immune responses, nutritional condition and production of Ompok pabda between the traditional culture system with stocking density of 17 (TS1), 22 (TS2) and BFT system (C: N ratio of 20:1; molasses as carbon source) with 17 (BFTS1), 22 (BFTS2), 27 (BFTS3) fish of 0.30 ± 0.001 g/m2; the fishes were reared with feeding a commercial diet at 10 − 3% of their body weight for 90 days in tanks. There was significant (p < 0.05) variation in water quality parameters including dissolved oxygen, pH, total ammonia nitrogen (TAN) between the traditional and BFT tanks. The fishes of the BFTS1 had the highest specific growth rate (SGR, 4.11 ± 0.17%/day) and survival (98.33 ± 2.89%) while the TS2 had the lowest SGR (3.51 ± 0.05) and survival (86.67 ± 5.03%). The protein, lipid, essential amino acids, monounsaturated fatty acid and polyunsaturated fatty acid contents were found higher in the BFT-reared fishes compared to the TS-reared fishes. The fishes of the BFT system had also higher red blood cell (3.28x106/mm3), hematocrit (34.5%), and neutrophil counts (27.30%) than had the TS-reared fishes. Regarding profitability, the BFTS2 provided the highest benefit-cost ratio (BCR; 1.22 ± 0.04) whereas the TS1 system had the lowest BCR (0.99 ± 0.04). Altogether, the obtained results points out that the stocking density modulated the rearing environment, and thus, production of O. pabda traditional and BFT systems; considering FCR and BCR values, the stocking density of 22 fish/m2 can be feasible to bring about good economic return of a O. pabda biofloc system.

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The study was conducted to evaluate growth, survivability, and proximate composition of Lizaparsia at different salinities to adopt as a potential aquaculture species in salinity intruded coastal areas ofBangladesh. The experiment was carried out at laboratory conditions in rectangular tanks (25 L) with fivedifferent salinities viz. 0, 5, 10, 15 and 20 ppt correspondingly considered as T1(control), T2, T3, T4 andT5. Fingerlings were collected from the Pashur river and stocked at 10 individual/25L tank. After 90 days ofculture period, growth was found significantly different among the treatments. Average weight gain washighest inT2 (1.76±0.19) and lowest inT5 (0.91±0.15). Interestingly survival rate was found 100(%) in alltreatment. Specific growth rate was 0.829±0.10, 1.162±0.14, 0.744±0.2, 0.736±0.10 and 0.605±0.15respectively in T1, T2, T3, T4 and T5. Average daily gain was found higher in T1 (0.059± 0.006g/d),compared to other treatment. The average food conversion ratios were 0.78±0.06, 1±0.00, 0.69±0.06,0.78±0.22 and 1.035±0.25 in T1, T2, T3, T4 and T5 in five tanks, respectively. Better water qualityparameters were observed in T2. The temperature ranged from 28-30.3ºC, pH from 7.21-7.64, DO from5.01-5.68 ppm, hardness from 184.55-237.65mg/l and total ammonia nitrogen (TAN) ranged from 0.52-0.85mg/l. No significant change was observed in the proximate composition of fish reared at different salinities.Finally, it could be concluded that L. parsia can tolerate a wide range of salinity and can be cultured even infreshwater, thus might be a potential species for coastal aquaculture.