In this investigation, it was aimed to evaluate the toxicity potential of water soluble fractions of crude oil histopathologically in order to identify the problems originating from water soluble fractions of crude oil in Xiphophorus helleri. An acute toxicity experiment was performed by exposure to three concentrations (10%, 20%, 40%) of water soluble fractions of crude oil on the specimens for 24, 48, 72 and 96 hours. The tissues of control and experimental groups prepared by the Hematoxylin-Eosin staining method, examined under light microscope, by passing through routine histological process. In parallel with the increase in concentration it was seen to be increase in histopathological findings in the gills. It was observed that disorganization of secondary lamellae, hyperplasia and fusion in the form of ballooning depending on the exposure time as deteriorating in the test group of 10% concentration. It was observed that adhesion in addition to obvious irregularity in secondary lamellae, hyperplasia which is more pronounced especially in the distal ends of the lamellae, lamellar edema and epithelial separation in parallel with increasing exposure time in the test group of 20% concentration. It is in question that the findings increasingly worsening depending on the increase of time in the test group of 40% concentration. It was observed that hypertrophy in mucous cells and increase in the amount of mucous secretion, hyperplasia in the maximum level in balloon appearance at distal ends of secondary lamellae in addition to proliferation of mitochondria-rich cells and mucous cells as more pronounced than other test groups. As a result, it was concluded that water soluble fractions of crude oil exposure will primarily effects primitive vertebrates in particular Xiphophorus helleri, and also will effects all vertebrates by means of food chain and interactions of living groups in generally, all living things will suffer due to crude oil intoxication to aquatic environments.