Major carps, native freshwater fish in South Asian nations, are economically valuable fish species with high market demand. Coastal rural people can cultivate them in their own seasonal, largely underutilized, small homestead ponds with low input and understanding. However, the major problems with fish production in this region are the lack of quality carp seed and appropriate culture techniques. Therefore, this research was carried out on growth performance, survival rate, yield, feed conversion ratio (FCR), and profit of carp polyculture systems stocking with hatchery-produced and wild sourced fish seed in homestead ponds located in a coastal area along the Bay of Bengal. Three different treatments (T1–T3), each treatment with three replications, were designed for culturing carps, Gibelion catla, Labeo rohita, Labeo calbasu, and Cirrhinus mrigala using two local hatcheries seeds (T1 and T2), and wild seeds from the Halda River (T3). For all treatments, the stocked fish were maintained in the same size, weight, density, and ratio. Water quality parameters were measured at intervals of seven days, and the mean values were found to be within an acceptable range for fish farming and, in most cases, did not differ significantly from each other. The specific growth rate (SGR) was found higher in T3 for G. catla (1.16 ± 0.012%/day), L. rohita (1.19 ± 0.035%/day), and C. mrigala (1.06 ± 0.03%/day) and significantly differed (p < 0.05) among the treatments. Additionally, there were significant differences between the treatments in terms of ultimate weight, weight gain, survival rate, fish production, and return on investment (ROI) (p < 0.05). The lower FCR in T3 (2.65 ± 0.10) than in T1 (3.32 ± 0.31) and T2 (3.21 ± 0.33) indicated that stocking wild seed had higher profitability potentials. High genetic variety in the population of naturally occurring, free-living fish, resistance to disease, a high rate of survival, and the hardiness of wild seed are all factors that might contribute to the better performance of wild seed stock. However, the total yield and total return from the T3 treatment also emphasized that carp farming using wild seed is not viable because of the variable amount, high seed cost, low transportation facilities, and very small natural seed-stock supplies from the river. Inbreeding and reduced genetic variety in the hatchery stock could result in the production of poor-quality seed, which had an impact on the production performance in culture treatments stocked with hatchery seed.

Macrobenthos play an important role in estuarine ecosystems by re-suspending the bottom layer of water bodies and elevating the nutrients, dissolved gases, and other materials between sediments and overlying water. The study aimed to measure the physicochemical parameter of the study area, to show the intertidal variation of macrobenthos, and to assess the relationship between environmental variables and benthic infauna of saltmarsh habitat along the Noakhali coast. Sediment infauna of saltmarsh was collected by using a hand-held mud corer having an area of 0.01 m2 covering three tidal levels i.e., high tide level (HTL), mid-tide level (MTL), and low tide level (LTL). A little variation was observed among the environmental parameters across three tidal levels. A total of 16 taxa of benthic infauna belonging to Nereidae (37.60%), Nereidae-1 (12.60%), Chironomidae (24.56%), Cerambycidae (2.17%) were found in the three tidal levels. The Evenness index indicated the highest number of similar species were at the sub-stations of LTLs with a value of 1, and the lowest number of similar species was at the sub-station HTL1 with a value of 0.5712. The maximum Shannon diversity (HꞋ) index was found at the sub-station MTL2 with a value of 1.631 and the minimum was at the sub-station LTL2, LTL3 with a value of 0. Margalef species richness ranged from 0 to 0.8808 and the Equabilitty index (J) value from 0 to 0.8808. The diversity profile was high (α=14) at the mid-tide level. The Simpson (1-D) and DO, Shannon ( HꞋ), Margalef, and temperature were significantly correlated (p < 0.05). Again, almost all diversity indices showed a strong correlation with temperature (0.75 ≤ r <1). The information generated here can be used to measure the impact of pollution, to conserve the biodiversity of the study area, and can also be used for further studies.

Algae are the naturally produced food for fish in any aquatic ecosystem and an indicator of a productive pond. However, excess abundance of harmful algae can have detrimental effects on fish health. In this study, the algal communities of 30 coastal homestead fish ponds were investigated to identify the diversity, assemblage and controlling environmental variables of harmful algae from a tropical coastal area. The findings showed that 81 of the 89 genera of identified algae were harmful, with the majority of them being in the classes of Cyanophyceae (50.81%), Chlorophyceae (23.75%), Bacillariophyceae (9.5%), and Euglenophyceae (8.47%). Microcystis spp. alone contributed 28.24% to the total abundance of harmful algae. Significant differences (p < 0.05) in algal abundance were found among the ponds with the highest abundance (470 ± 141.74 × 10³ cells L⁻¹) at pond (S₂₅) near agricultural fields and the lowest abundance (109.33 ± 46.91 × 10³ cells L⁻¹) at pond (S₁₄) which was lacking sufficient sunlight and nutrients. Diversity indices, e.g., dominance (D), evenness (J′), richness (d) and Shannon diversity index (H′) ranged from 0.17 to 0.44, 0.23 to 0.6, 0.35 to 2.23 and 0.7 to 1.79, respectively, indicating a moderate range of diversity and community stability. Community composition analysis showed the assemblage was dominated by Cyanophyceae, Chlorophyceae and Bacillariophyceae, whereas, multivariate cluster analyses (CA) identified 11 major clusters. To identify the factors controlling their distribution or community assemblages, eight environmental variables (temperature, pH, dissolved oxygen (DO), salinity, transparency, nitrates, phosphates and sulphate) were measured. ANOVA analysis showed that the variables significantly differed (p < 0.05) among the ponds, and canonical correspondence analysis (CCA) demonstrated that DO, nitrates, phosphates, sulphates, salinity and transparency have the most impact on the abundance of algal genera. In addition, analyses with Pearson’s correlation coefficient showed that the abundance of total algae, diversity and community were mainly governed by phosphates and sulphates. These results can be used to identify and control these toxic algal groups in the local aquaculture sector.

Scylla olivacea is regarded as a nutritionally and economically demandable species, however, there lies a paucity of information on this mangrove crab. Therefore, the objective of the present study is to assess the biochemical composition and caloric values of different body parts of female S. olivacea. The crab samples (100-150g) were collected from a mangrove area of Bagerhat district, the Southern part of Bangladesh from November 2019 to February 2020. The biochemical composition (moisture, protein, lipids, ash, and carbohydrate) and the energy value of the samples were analyzed following standardized methods. The moisture content varied from 38.99±1.29g to 75.15±0.78g per 100g of crab. The carbohydrate level was in the range of 2.89g/100g to 27.77g/100g, while protein content ranging from 0.65±0.10g/100g to 19.24±0.90g/100g. Per 100g of crab, the lowest amount of fat (0.40±0.14g) was observed in the bone while the highest amount (1.79±0.17g) in claw meat. Bone provided the highest amount of ash (32.20±0.69g/100g) and energy (117.34kcal/100g) than other body parts of the crab. The present study reveals that female S. olivacea is high in protein and low in fat providing a good amount of energy. Hence, research on S. olivacea and other crabs commonly found in Bangladesh should be expanded to get a more comprehensive knowledge of their nutritional profile and health benefits.

Homestead ponds are small seasonal ponds that are rarely utilized for fish farming. Culturing fish in these small ponds can boost household fish consumption and cash inflow. The availability of nutrients in the water and sediment, however, plays a significant role in the pond’s natural productivity. This study was conducted to assess nutrient contents and some key physical parameters in the bottom sediments of 30 homestead ponds from the central coast along the Northern Bay of Bengal. Analyses of results showed the average values (±SD) of temperature, pH, electrical conductivity, organic matter (OM), organic carbon (°C), nitrogen (N), phosphorus (P) and sulphur (S) were 17.8 ± 1.12 °C, 7.29 ± 0.11, 0.41 ± 0.09 mS/cm, 29,615.48 ± 10,528.9 mg kg⁻¹, 11,958 ± 6107 mg kg⁻¹, 1030.6 ± 252 mg kg⁻¹, 17.1 ± 13.5 mg kg⁻¹ and 32.6 ± 19.7 mg kg⁻¹ during winter and 27.2 ± 1.81 °C, 6.73 ± 0.12, 0.38 ± 0.17 mS/cm, 19,100.01 ± 13,739.07 mg kg⁻¹, 11,079 ± 7969 mg kg⁻¹, 955 ± 229.4 mg kg⁻¹, 26.6 ± 20.2 mg kg⁻¹ and 23.4 ± 15.9 mg kg⁻¹ during pre-monsoon, respectively. One-way ANOVA revealed no significant differences in the mean value of sediment quality parameters among the selected ponds (p > 0.05) except for phosphorus in the winter season (p < 0.05). The sediment quality variables were found to be in the suitable range for fish culture. Pearson’s correlation coefficient values (r) showed that only organic carbon and nitrogen had a strong significant correlation with organic matter (p < 0.05). Based on Cluster Analysis (CA), two major associations among the nutrients were attained at a 15% similarity level: C, OM, and N in one cluster and P and S in another. The findings showed that the parameters were within the preferable range for aquaculture, and the homestead ponds are average productive ponds.

Plankton is essential to estuarine food webs, providing key food for species like fish larvae, and understanding their dynamics helps us comprehend ecological interactions and energy transfer in aquatic ecosystems. This study examined the plankton community structure, diversity, variability and the environmental variables of water that influenced these communities in a freshwater-dominated estuary along the Northern Bay of Bengal during the dry season. A variety of tools were employed, including a dissecting microscope, a Sedgwick-Rafter cell, and a Hanna multi-parameter meter, to obtain detailed and comprehensive data. From the analyses, in total 37 genera of phytoplankton belonging to 11 classes such as Bacillariophyceae (66%), Coscinodiscophyceae (28%), Fragilariophyceae (1%), Euglenophyceae (1%), Cyanophyceae (1%), others (3%) were recorded. Zooplankton, consisting of multicellular organisms, was represented by 11 genera across five classes, with Monogononta (53%) and Insecta (29%) being the most prevalent. Phytoplankton exhibited a mean abundance of 180,000 ± 20,200 cells l⁻¹ whereas zooplankton showed a mean abundance of 3,000 ± 200 cells l⁻¹. The diversity indices (H′), evenness (J′) and dominance (D) ranged from 1.188 ± 0.015 to 0.19 ± 0.006, 0.9377 ± 0.002 to 0.5118 ± 0.006, 0.365 ± 0.001 to 0.143 ± 0.002 respectively, suggested low to moderate plankton diversity with a suppressed community and moderate to high dominance in the river water. Based on the similarity percentage (SIMPER) and analysis of similarity (ANOSIM), Phytoplankton and zooplankton varied significantly between stations while non-metric multi-dimensional scaling (nMDS) indicated greater consistency in phytoplankton communities across stations compared to zooplankton. Furthermore, Pearson’s correlation coefficient (rs) and canonical correspondence analysis (CCA) identified transparency, sulfates, dissolved oxygen, conductivity, TDS, pH, and salinity as major influencers of plankton abundance; nitrate had a moderate effect. Spearman’s rank correlations showed significant positive (p < 0.05) correlations between diversity indices and environmental variables. Future research should focus on long-term monitoring and the potential impacts of environmental changes on plankton communities.