10.22376/ijpbs.2019.10.1.p1-12 Volume 12 Issue 1 2021 (January-March) Arrah is an agricultural area of Bihar dominated by the paddy culture. Tricyclazole (mol formula: C lessThan sub greaterThan 9 lessThan /sub greaterThan H lessThan sub greaterThan 7 lessThan /sub greaterThan N lessThan sub greaterThan 3 lessThan /sub greaterThan S; molecular mass: 189.24 g/mol), a systemic and sulphurated fungicide is recommended to treat blast disease caused by lessThan i greaterThan Pyriculariaoryzae lessThan /i greaterThan in irrigated rice. lessThan i greaterThan Channapunctatus lessThan /i greaterThan (Bloch) or snake-headed murrel is an Indian freshwater air-breathing fish also found in paddy fields. This maiden study was designed to evaluate the acute toxicity of tricyclazole and its responses to certain haematological indices in lessThan i greaterThan Channapunctatus lessThan /i greaterThan . By the Finney probit method, a 96hr-LC lessThan sub greaterThan 50 lessThan /sub greaterThan dose of tricyclazole for this fish was calculated as 22.44 mg/L. The calculated LC lessThan sub greaterThan 50 lessThan /sub greaterThan dose indicates the highly toxic nature of tricyclazole. Haematological indices were studied following standard methods. The test fish were exposed to 0.25 and 1.25 mg/L sublethal dose of tricyclazole for a long term (15, 30 and 45 days) exposure and the variations of haematological indices were determined. The results demonstrated that total erythrocyte count, haemoglobin, packed cell volume, basophils, neutrophils, monocytes and thrombocytes decreased significantly (p lessThan 0.05) while erythrocyte sedimentation rate, total leucocyte count, eosinophils and lymphocytes increased significantly (p lessThan 0.05) in all long term treated group of fishes when compared to its control group. These variations were observed dose-dependent and also duration-dependent to combat stress response raised due to tricyclazole toxicity. There is no concern about its application in nature at the concentrations recommended for control of the disease. Therefore, the entry of such fungicide to natural water bodies should be stopped besides ensuring their judicious application around the catchment area. Further, these findings may be used in the assessment of the potential risk of tricyclazole on the food chain and aquatic ecosystems. Dina NathPandit, Usha Rani and MohitaSardana Tricyclazole, 96hr-LC50, Long term toxicity, Haematological indices, Channapunctatus. 97-103