Experimental assessment of the histopathological effects of water-soluble fraction of crude oil on gill tissue of juvenile Rutilus frisii kutum

The toxic effects of water soluble fraction (WSF) of crude oil on the gills of juvenile kutum roach, Rutilus frisii kutum, were investigated. The juvenile (1-2g) kutum roach were collected in summer 2008 from the Kolmeh Hatchery Center, Golestan province, and acclimatized to laboratory conditions through keeping them in a 300 liter tank with dechlorinated water for a minimum of 8 days. Six different types of WSF concentrations were made to obtain LC5096h including 27, 29.25, 31.5, 33.75, 36 and 38.25ppm. Then, 10 fingerlings of R. frisii kutum were exposed to the WSF concentrations, for 96 hours. Considering mortality rate of the juveniles in 96 hours and using Probit value statistical analysis, LC5096h was obtained at 33.95ppm. Two different concentrations (0.1 LC50 and LC50) of WSF were prepared for further assessments and after 24 and 96h of exposure, 3 individual fish were collected from each aquarium for histopathological studies. The gill sections with 3 micron thickness were prepared, stained using H & E, and examined by light microscope. General damages after observation included: Epithelial lifting, congestion in filament and lamellae, clubbing, fusion, hypertrophy of epithelial cells of lamellae, different levels of hyperplasia between lamella and aneurysms. Pathological studies showed that the WSF of crude oil causes serious damage in gills of juvenile R. frisii kutum, leads to malfunction of this organ which will harm homeostasis of the fish.