The extensive use of pesticides to control agricultural pests poses a serious threat to organisms of the aquatic environment. Chemicals entering the aquatic ecosystem through human activities, either accidentally or by design may cause adverse effects on the aquatic biota, including deleterious changes which disrupt metabolic activity at the biochemical levels. In the present study the impact of Endosulfan, Chlorpyrifos and Carbaryl on hepatopancreas of Fiddler crab, Uca triangularis was studied. Histological alterations and biochemical changes such as acid phosphatase (ACP), alkaline phosphatase (ALP), succinate dehydrogenase (SDH), lactate dehydrogenase (LDH) activities in hepatopancreas had been carried out. The deceased hepatopancreas revealed infiltration, formation of large lumen and disappearance of haemocytes. The LDH and ACP activity was increased in Hepatopancreas while SDH and ALP activity was decreased in treated groups. Overall work concluded that histological biomarkers provide reliable data to discriminate the usage of pesticides which had direct influence on loss of aquatic animals.