A 120-day cage grow-out production performance of Nile Tilapia, Oreochromis niloticus was conducted in the Dakatia river, Echoli, Chandpur to identify an optimal stocking density. The three stocking densities were used at 30, 50, and 70 tilapia m-3 under three treatments with triplicate. The initial average weight of tilapia fingerlings at 32.31±9.59 g was stocked. Final weight, specific growth rate, and survival were significantly (p < 0.05) higher in the 30 tilapia m-3 stocking density than those in the 50 and 70 tilapia m-3 stocking densities. The best food conversion ratio of 1.47 was found in the 30 tilapia m-3 stocking density and followed by 2.0 and 2.90 in the 50 and 70 tilapia m-3 stocking densities, respectively. The production was comparable (p > 0.05) between the 50 and 70 tilapia m-3 stocking densities; however, the net profit was higher (p < 0.05) in the 50 tilapia m-3 stocking density group compared to the two other stocking density groups. This study suggests a stocking of density at 50 tilapia m-3 to increase Nile Tilapia O. niloticus productivity in the riverine cage culture system. Bangladesh J. Zool. 50 (2): 239-250, 2022

Shrimp aquaculture plays the key role in Bangladesh seafood export industry. It includes the species of Tiger prawn Penaeus monodon, and Giant river prawn Macrobrachium rosenbergii, which have been widely farmed after 1980s. The industry is severely damaged due to diseases outbreaks in hatcheries, nurseries and grow-out ponds since 2000, thus this sector shows shrinkage from global export market. However, the last few decades an alternate aquaculture decapod species, Whiteleg shrimp Litopenaeus vannamei has been recognized as the most important in world-seafood export item. Bangladesh aquaculture has very recently been introduced with the Whiteleg shrimp L. vannamei for shrimp production boost up. This review focusses on the current state of arts for L. vannamei aquaculture techniques and their possible implication to farming in Bangladesh. Recently, several Whiteleg shrimp pilot scale farming were initiated which showed promising production ranged from 5.0 to 8.9 MT/ha. Private entrepreneurs now become interested and it is perceived that the Whiteleg shrimp could gear up shrimp production in near future in terms of better production performance, technology development and extension work besides other indigenous culture-shrimp species. By introducing this shrimp, we forecast that, depending upon the technology adoption in present culture areas, the export frozen seafood earnings from shrimp sector will increase up to 5 to 10 folds from the present. Thus, proper understanding and knowledge based innovative approach for its sustainable rapid extension and strategies is in need. This review suggests the regional reproducible pilot culture program for hatchery, nursery and grow-out under controlled environment ensuring better footprint and low residues impact to natural aquatic systems. Adaptive research should be initiated to develop intensive or super-intensive culture techniques besides the traditional practices in the selected confined areas. The pond culture, biofloc farming, aquamimicry farming and green water raceways could be excellent options for L. vannamei culture in Bangladesh. Bangladesh J. Zool. 50 (2): 143-184, 2022

Seaweeds are one of the most potential aquaculture commodities in Bangladesh. It has a long back history of being used for its nutritional and pharmaceutical importance. This review summarizes seaweeds diversity and its culture, distribution and possible applications and uses in Bangladesh. Seaweed floras are distributed along the entire coastline, however, the higher abundance of these have found in the St. Martin Island, Cox's Bazar, and Sundarbans mangrove forest periphery. These included around 200 species and belong to 94 genera. About 12 of these genera, including Hypnea, Gracilaria, Gelidium, Enteromorpha, Halimeda, Padina, Dictyota, Caulerpa, Hydroclathrus, Sargassum, Kappaphycus, and Porphyra have substantial commercial importance. A total of 5,000 metric tons of seaweeds are likely available along the entire coastline between October and April. However, seaweeds commodity and its aquaculture production have a great potential in the coastal region of Bangladesh. Furthermore, the sustainable development of this industry could bring numerous benefits such as rural development, employment opportunity and income generation, women empowerment, disease prevention, and proper utilization of land. Therefore, this sector needs more attention for its expansion activities include culture, usages and bioactive compound developments. Additionally, seaweeds cultivation could have numerous environmental benefits include ecosystem services, removal of hazardous nutrients and pollutants, metal toxicants uptake, in turn estuaries and seas tackle pollution in natural process. Bangladesh J. Zool. 50(3): 283-307, 2022

This study examined the intensification of mono-sex Nile tilapia Oreochromis niloticusaquaculturein riverine net cages installed at the River Dakatia, Roghunathpur, Chandpur. This study performed 120-day cage grow-out trials with densities of 50, 75, and 100 tilapia m-3 under three replications with an average initial weight of 28.92±8.37g per juvenile fish. The monthly water quality parameters (temperature, pH, dissolved oxygen, total alkalinity and hardness, ammonia-N and Nitrite-N) in the cage installation water area of the River Dakatia were found to be suitable for tilapia cage culture. The monthly average weight gain was significantly (p < 0.05) higher in 50 tilapia m-3 stocking density than in the other two stocking densities tested. The mean final weight and specific growth rate were significantly (p < 0.05) higher in 50 tilapia m-3 stocking densitythan the other two stocking densities. Significantly (p < 0.05) higher survival (97.92%) was found in the 50 tilapia m-3 stocking density group and followed by 86.74% and 84.39% in the 75 and 100 tilapia m-3 stocking densities, respectively. Consequently, the monthly relative and specific growth rate and feed conversion ratio were significantly (p < 0.05) higher in 50 tilapia m-3 stocking density fishes for the first, third, and fourth months. Gross production was comparable between 50 and 75 tilapia m-3 stocking densities but was significantly (p < 0.05) better than 100 m-3 stocking density. Net production was significantly (p < 0.05) higher at 50 tilapia m-3 stocking density group than those of 75 and 100 tilapia m-3 stocking densities. The best feed conversion ratio (1.60) was in the 50 tilapia m-3 stocking density group (p < 0.05) than those of 1.87 and 2.44 for the stocking of 75 and 100 tilapia m-3, respectively. Benefit-cost ratio and net profit were significantly (p < 0.05) better at 50 and 75 tilapia m-3 than at 100 tilapia m-3 stocking density. Therefore, considering maximum outputs, benefits, and performances, we recommend stocking density at 50 mono-sex tilapia m-3 for the best growth, cost-effective production, and highest-economic return from 120 days of grow-out net cages in the riverine culture system. J. Bangladesh Acad. Sci. 47(1); 43-52: June 2023