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Abstract:

An experiment was conducted to evaluate the effects of stocking density on growth and survival of Nile tilapia (Oreochromisniloticus) in brackish water earthen pond. Fish with initial weight of 13 g kept in three stocking density 3, 6 and 9 fish/m₂ in duplicates and were fed on rainbow trout feed for 105 days during the light period. The results showed significant reduction in final weight, weight gain, daily growth rate, specific growth rate and survival by increasing stocking density, while feed conversion ratio enhanced in higher stocking densities (p< 0.05). Among the treatments evaluated, 3 fish/m² showed the best growth rate and survival, and the lowest feed conversion ratio. So, it seems that to achieve the highest profit, the stocking density of 3 fish/m² is suitable for culturing of tilapia in earthen pond. 

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Food safety is a global concern, yet little research has focused on the heavy metal (HM) pollution and health risks associated with both cultured and captured fish. This study evaluates the bioaccumulation and human health risks of HM (Cd, Cu, Zn, Cr, and Pb) in various tissues of aquacultured fish, Oreochromis niloticus, from major lakes in Bengaluru. Over two years (August 2021 to July 2023), spanning different seasons, fish samples were collected and analyzed for heavy metal presence using Atomic Absorption Spectrophotometry (AAS). Bioaccumulation levels were assessed, along with Estimated Daily Intake (EDI), Target Hazard Quotients (THQ), Hazard Index (HI), and Target Risk (TR). Results showed varying bioaccumulation patterns across different tissues and lakes. The highest concentrations of heavy metals were found in gonad and liver tissues HI values for all muscle tissue were > 1, indicating potential health risks from metal consumption. TR levels were found to be unacceptable in the case of Cd and Cr which may lead to the risk of cancer and damages the normal functionality of the kidneys and liver. This study highlights the health threats associated with consuming freshwater fish from Ulsoor and Agara lakes in Bengaluru, underscoring the importance of regular lake monitoring to mitigate heavy metal impacts on human health and the ecosystem.