Fishes are very important food resources in developing countries like India. But due to indiscriminate use of the chemicals in the agriculture lands and other fouters the whole aquaculture ecosystem is adversely affect including fishes. The present study intended to assess the toxicity of Chlorpyrifos (20% EC), a popular organophosphate pesticide commonly used in agriculture fields, in a freshwater air-breathing fish Anabas testudineus in laboratory conditions. The fishes were exposed to different concentration of Chlorpyrifos and LC50 (15.5 ppm) was evaluated. Experimental fish have been exposed to several sublethal concentrations (1/10 and 1/50th of the LC50 value) for 15th, 30th, and 45th days, respectively, to assess certain haematological parameters (RBC and WBC count, Hb percentage, and PCV value). The impact was examined by comparing data between control and experimental groups of fish. The RBC and WBC count, Hb percentage and PCV value were found significantly decrease (P< 0.05) in compare to control group. Some behavioural changes, such as restlessness, irregular movement, hyperactivity, and so on, were observed in fish exposed to Chlorpyrifos. This was the result of stress produced by an abrupt shift in environment or the inactivation of a specific enzyme (acetylcholinesterase) activity. Hence it is recommended to use the pesticide at the lowest possible concentration to control and also to preserve the land and aquatic ecosystem for sustainable development.





