Histopathological study of gill lesion of rainbow trout in cold water fish farm of Kohgiluyeh Boyer Ahmad province

Because of the direct contact of the fish with water that contain of fish excrete metabolite and chemical pollution;it is one of the most susceptible organs of fish. In this study variety of gill lesions of rainbow trout were studied in cold water fish farm. This study has been carried out on 30 samples from 2 farms of rainbow trout culture (2 of extensive culture farm) in Kohgiluyeh Boyer Ahmad province.After gross examination¡ for microscopic study¡ a 1×1×1 piece of gill was separated and immediately fixed in 10%neutral buffered formalin.Then processed routinely and embedded in paraffin and cut with microtom in thickness 5 μm¡ and stained with Hematoxylin – Eosin.Histopathological study revealed 27% edema and hyperemia. However other microscopic lesion including of hypertrophy (20%)¡ telangiectasia(10%)¡ inflammation of the basal membrane of secondary lamella(10%)¡ hyperplasia and fusion of secondary lamella(13%) and clubbing(10%) in some cases in the gill were also seen. In 17% of 30 specimens¡there were no lesions in gills.