Fishes infected with Adenoscolex oreini appeared anemic and the abdomen viscera appeared red on opening the abdomen and the abdominal fluid was tinged red. On opening the intestine necrotic debris was present on the surface and numerous parasites were pesent. The histopathological alterations observed in the intestine of fish were (severe degenerative and necrotic changes in the intestinal mucosa as well as edema between submucosa and mucosa). In parasitized Schizothorax niger, hyperplasia of

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... testinal mucous cells and enhanced mucus secretion were also noticed. Cestode bodies were covered with an adherent mucus blanket. The analysis of the seasonal variation on the histological parameters leads to the conclusion that the distribution or the severity of the lesions observed in the these organs were not related to the seasons. Such information confirms that histopathological alterations are good biomarkers for field assessment, in particular in tropical areas that are naturally subject to a multiplicity of environmental variations. It must be emphasized that histopathology is able to evaluate the early effects and the responses to acute exposure to parasitic infections and chemical stressors.