Sensitivity of medaka (Oryzias latipes) to 4-nonylphenol subacute exposure; erythrocyte alterations and apoptosis.

The present study was undertaken to assess the effects of the endocrine-disrupting compound; 4-nonylphenol (4-NP) in medaka (Oryzias latipes). The frequencies of erythrocyte alterations, apoptosis, and micronuclei were used as biological indicators of damage. Medaka were exposed 15 days to 4-NP at three sublethal concentrations (50, 80, and 100 μg/l 4-NP) and results compared with those of a previous study using catfish as an animal model. Exposure of medaka resulted in a dose-dependent increase in the frequency of erythrocyte alterations, apoptosis and micronucleus (MN). Many morphological alterations and nuclear abnormalities were observed, including acanthocytes, lobed nucleus, eccentric nucleus, fragmented nucleus, blebbed nucleus, binuclei, deformed nucleus, notched nucleus, hemolysed cells, crenated cells, teardrop-like cells, and schistocytes. Mortality was recorded after treatment with 80 and 100 μg/l 4-NP, indicating that medaka are more sensitive than catfish to 4-NP exposure. We concluded that, 4-NP causes several malformations in the shape and number of erythrocytes in medaka, indicating its genotoxicity.