Effect of long-term hypoxia on the reproductive systems of female and male yellow catfish (Pelteobagrus fulvidraco)

This study investigated the effects of different levels of hypoxia on the reproductive system of yellow catfish. Yellow catfish (Pelteobagrus fulvidraco) were exposed to three dissolved oxygen concentration levels: normoxia (6.5 ± 0.2 mg/L), moderate hypoxia (MH, 3.8 ± 0.3 mg/L) and severe hypoxia (SH, 1.9 ± 0.2 mg/L) for 30 days. The gonadosomatic index of males, not females, significantly decreased in the SH group. In the SH group, for the females, the ratio of vitellogenic follicles significantly decreased, whereas the number of atretic follicles significantly increased. In male fish, a significantly reduced number of spermatozoa was observed in both the MH and SH groups. Elevated apoptosis levels in the testes and ovaries were observed only in the SH group. Serum 17β-estradiol and vitellogenin levels in females and testosterone levels in males significantly decreased in the SH group. The concentration of 11-ketotestosterone in males significantly decreased in both the MH and SH groups. In female fish, dysregulated expression of the hypothalamic-pituitary-gonadal (HPG) axis, steroidogenesis genes, and hepatic genes related to vitellogenesis were observed only in the SH group. However, in male fish, moderate hypoxia altered the expression of HPG genes, including gnrh1, lhcgr, and amh. Moreover, the MH group significantly altered the expression of steroidogenesis genes like star, 17β-hsd, and cyp17a1. The results of this study suggest that severe hypoxia can cause reproductive defects in female and male yellow catfish. Moreover, the reproductive system of male yellow catfish is more sensitive to moderate hypoxia than that of female catfish. Our findings contribute to our understanding of the response of the teleost reproductive system to long-term hypoxia.