Abstract

• The histological changes found in the gills of the Oreochromis sp. were investigated from June 2018 to July 2019, in Nyaung Kaing In (Lake), Monywa Township. The seasonal histological investigation in the gills of Oreochromis sp. revealed abnormalities such as curling and club shaped of lamellae, incomplete and complete fusion of lamellae, shortening of lamellae, degeneration and desquamation of lamellae, dilation of gill filaments and arches, hyperplasia and hypertrophy of gill filaments, separation of gill filaments, elastic cartilage, haemorrhage of gill filaments, edema of gill arch, blood congestion of gill filaments and arches, cysts with parasites in gill filaments, aneurysms and epithelial lifting were observed. Physicochemical parameters of water quality analyzed seasonally revealed that parameters such as dissolved oxygen, total alkalinity, and ammonia nitrogen were beyond the acceptable limits in some seasons of study period .The other parameters showed within the normal range. Biochemical oxygen demand was higher than the permissible limit during three seasons. Heavy metals such as arsenic, copper, cadmium and lead values analyzed seasonally within the permissible limits.