Extensive usage of silver in several applications may contaminate the freshwater compartment and affects the health status of aquatic organisms. In the present investigation, fingerlings of Indian major carp Labeo rohita were exposed (35 days) to sublethal concentrations of silver nitrate (AgNO3) and bioaccumulation pattern, biochemical and histological alterations were evaluated. Initially, the median lethal concentration (LC 50) of silver nitrate to the fish Labeo rohita for 96 h was calculated and it was found to be 0.035 mg L−1. To assess the toxicity of ionic silver two sublethal concentrations (0.0035 mg L−1: 1/10th of LC 50 and 0.007 mg L−1; 1/5th of LC 50) were selected and the experiment was conducted for a period of 35 days. A considerable quantity of AgNO3 was accumulated in the gill, liver and kidney tissues of Labeo rohita. Accumulation of AgNO3 was high in liver tissue compared to other organs/tissue. Membrane-bound enzyme (Na+/K+/-ATPase) activity was inhibited in both the concentrations when compared with the control group. Likewise, plasma electrolytes (Na+, K+ and Cl−) level were significantly decreased when compared with untreated groups. On the other hand, a noticeably increased level of glucose was observed in fish exposed to 0.0035 and 0.007 mg L−1 of AgNO3. Moreover, declining protein level was assessed during the initial days (7 and 14 days), and the level was increased in the rest of the exposure period. Extensive histopathological abnormalities were noticed in gill (hyperplasia, epithelial lifting, curling of lamellae) and liver (degeneration of hepatic nucleus, vacuolization, hepatic necrosis) of fish treated with silver nitrate when compared to control groups. The results obtained in the present study revealed that the bioaccumulation pattern, alterations in membrane-bound gill-ATPase activity, plasma electrolytes, biochemical and histological parameters of fish can be useful for biomonitoring the changes in the environment and health condition of fish in freshwater ecosystem contaminated with silver.
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