Effects of nonylphenol on ovarian and testicular tissues in immature rainbow trout (Oncorhynchus mykiss)

Nonylphenol (NP) is an endocrine disrupting chemical widely used in industrial practices worldwide. It is estimated that large amounts of this estrogenic compound annually discharged into aquatic ecosystem. So this study was conducted to determine the effects of this pseudoestrogen compound on gonadal maturation and histopathology of ovarian and testicular tissues of rainbow trout, Oncorhynchus mykiss. To this end, a total of 360 rainbow trout (115 ± 5 g) were randomly assigned into 6 groups with triplicates and intraperitoneally injected with ascending doses of NP (10, 50,100 μg/g body weight) or a single dose of E2 (2 μg/g body weight) or solvent control (ethanol-coconut oil), whereas controls were not injected. The injections were performed at three times in 0, 7, and 14 days in complete dose form and tissue sampling was carried out on the 21st day. The male and female gonads were fixed in Bouin's fluid and 6 μm sections were prepared using the standard histological method. The sections were stained by the standard H&E staining method and the stained sections were examined using light microscope. The results demonstrated that oocytes development is affected by NP and E2 treatments, but had no effects on process of spermatogenesis. Moreover, various histopathological lesions were observed in ovary and testis tissues of fishes exposed to different nonylphenol concentrations, so that damages significantly increased with increasing concentration. Histopathological alterations in ovaries included atretic oocytes, hyperplasia of granulosa layer, nuclear pyknosis, cytoplasmic vacuolation, damage of yolk granules and nuclear disintegration. Hyperplasia of interlobular connective tissue, fibrosis of lobules, hypertrophy of sertoli cells, abnormal distribution and degenerative of spermatogonia, cellular vacuolation, and pyknotic nuclei were the most important tissue lesions observed in testicular tissue. In general, the results showed that NP has the potential to cause significant effects on gamete development stages and causes various lesions on ovarian and testicular tissues.