The current study's goal was to look at how stocking densities affected Bheda (Nandus nandus) growth and production over the course of a 120-day period. Three treatments were T 1 (20,000 fish ha -1 ), T 2 (30,000 fish ha -1 ), and T 3 (40,000 fish ha -1 ), each with three replicates. Those fishes were fed daily with commercial sinking feed and a live food mixture at 9-3% fish body weight up to harvesting. Temperature, dissolved oxygen, pH, and other water quality indicators were measured every two weeks, along with the growth performance of Bheda fish. T 2 had the highest yield of Bheda (3439.08±207.31 kg ha -1 ), followed by T 3 (3422.78±224.42 kg ha -1 ), and T 1 (3136.62±150.00 kg ha -1 ). The harvesting weight (g), individual weight gain (g), individual percent (%) weight gain (g), SGR (% per day), and survival rate (%) of fish were significantly higher (p<0.05) in T 1 , followed by T 2 and T 3 , respectively, where combined production of fishes was significantly higher at T 2 followed by T 3 and T 1 . Net profit and benefit-cost ratio were significantly higher in T 1 than T 2 and T 3 . Based on the results of this experiment, it can be concluded that stocking density of Bheda fingerlings at the rate of 20,000 fish ha -1 in T 1 showed the highest production performance for profitable pond aquaculture. However, further research on the standardisation of stocking density with economic profitability of this fish at the on-station or on-farm level in ponds may be required before widespread dissemination of this culture technology to farmers, particularly in Bangladesh and elsewhere.

The study was conducted to evaluate the existing fish culture strategy and management practices in selected upazilas (viz., Mymensingh Sadar, Trishal, and Muktagacha) under Mymensingh district. The results showed that, the average pond area was ranged between 150 and 2000 decimal in Mymensingh Sadar, whereas it ranged from 100 to 1500 decimal in Trisal. However average pond area was comparatively higher in Muktagacha within 200-4000 decimal. The farmers of the study area adopted monoculture (50%). Whereas, one third (33.33%) of them preferred polyculture and a few (16.67%) followed both the culture systems. Preventive measures such as regular health checking (66.67%), drying of pond (66.67%) and applying lime in the pond (100%) were practiced in the studied farms. About 66.67% farmers used probiotics in their farms for beneficial purposes like water quality management, growth enhancement and disease resistance. 87.5% farmers acclimatized fry before stocking into the ponds at each selected upazila of Mymensingh district. Data showed that fish production was varied with culture types, areas, and culture period. The highest average production was in Trisal (158.5 Kg/decimal). Whereas, the average production in Mymensingh Sadar was (157.5 kg/decimal) and in Muktagacha was (143.5 kg/decimal). It was found that, the year-round production of Pangus was highest in Trisal 245 kg/decimal and lowest (150 kg/decimal) in Muktagachha. Tilapia production data showed the best production (77.5 kg/decimal) in Mymensingh sadar, whereas the lowest (65 kg/decimal) in Trisal. Data regarding the disease and health analysis of cultured ponds showed that there were four different types of diseases found in the study area including bacterial, viral, fungal and protozoan diseases. Most of the farmers took some preventive measures such as regular fish health checking, pond drying, application of lime, weeding the pond, removing water turbidity, addition of water etc. Almost all the farmers (100%) in the selected area, always apply lime in their pond and controlling of aquatic weed was found to be practiced by 41.67% farmers.

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The study was conducted to evaluate the existing aqua farming status and health management practices in 24 commercial farms located in selected upazilas (viz., Mymensingh Sadar, Trishal, and Muktagacha) under Mymensingh district. Data were aggregated through participatory rural appraisal (PRA) tools such as questionnaire interview, focus group discussion (FGD) and key informant interview. The findings uncovered that, the culture practice (monoculture and polyculture) was similarly preferred by the respondents. Both polyculture and monoculture systems were practiced in all of the selected Upazila. It was observed that most of the farmers of the study area adopted monoculture (50%). Whereas, one third (33.33%) of them preferred polyculture and a few (16.67%) followed both the culture systems. Only 33.33% farmers follow the sanitary facility which is important for security of biomass. 25% farmers monitored the farms on daily basis, while 37.5% farmers and 37.5% farmers monitored the disease condition weekly and bi-weekly, respectively. 12.5% farmers monitored the health condition of fishes on daily basis and 50% farmers monitored on bi-weekly basis in Muktagacha. On the other hand, 25% and 62.5% farmers monitored the health condition on weekly and bi-weekly basis, respectively in Trisal. About 25% farmers in the selected upazilas used different types of antibiotics and chemicals to control diseases. About 75% farmers did not use any types of antibiotics and chemicals to control diseases. The result showed that, 33.33% farm owners used probiotics in the pond for beneficial purposes where 25% of farms used water quality regulatory probiotics, 25% of farms used soil probiotics and 8.33% used gut probiotics. Most farmers (87.5%) have stocked diseased free fry from various hatcheries while a few (8.33%) supplied from their own hatchery.

An experiment was conducted to evaluate the proximate composition of Spirulina platensis and growth performance in supernatant of different concentrations (supernatant of 20, 40 and 60 rotten guavas) of digested rotten guava medium (DRGM). The growth rates in terms of optical density, dry cell weight and chlorophyll a of spirulina were varied from each other. The cell weight of Spirulina was attained a maximum of 0.818 ± 0.003 mg/L in 60% DRGM followed by 0.815 ± 0.0015 and 0.809± 0.0012 mg/L in supernatant of 20 and 40%, respectively on the 10th day of culture. Similar trend was also observed in the case of optical density of the media contained Spirulina, chlorophyll a content (mg/L), total biomass (mg/L), specific growth rates (on the basis of cell weight and chlorophyll a) and total biomass of Spirulina. Cell weight of Spirulina grown in these media had highly significant (P < 0.01) correlation with the chlorophyll a content (r = 0.746) and total biomass  (r = 0.742) of Spirulina. The growth performance of Spirulina in supernatant of 60% DRGM was significantly (P < 0.01) higher than that of grown in 20% and 40% DRGM. The percentage of crude protein was found 53.35 ± 0.32% in supernatant of 40% DRGM. The crude lipid was attained of 10.15 ± 0.14% in supernatant of 60% DRGM which was significantly (P < 0.05) higher than that of grown in 20% and 40% of DGRM.