Reproductive endocrine dysfunction in Atlantic croaker exposed to hypoxia

Although there is extensive evidence for impaired endocrine function in fishes exposed to environmental chemicals, information is currently lacking on reproductive endocrine effects of other environmental stressors such as hypoxia. The effects of ten weeks exposure to low dissolved oxygen (DO: 2.7 ppm and 1.7 ppm) on reproductive morphometric and endocrine responses in female Atlantic croaker ( Micropogonias undulatus) were investigated in controlled laboratory studies, and compared to the effects observed in fish collected from hypoxic sites in Mobile Bay, Alabama. Exposure of croaker to moderate hypoxia during ovarian recrudescence, both in the laboratory and at the field sites, caused significant impairment of ovarian growth as well as decreased production of fully grown oocytes, resulting in dramatic reductions in the number of viable gametes (fecundity). Ovarian dysfunction was associated with significant decreases in endocrine indicators of the estrogen signaling pathway regulating production of vitellogenin, the yolk protein precursor sequestered by the growing oocytes. The results indicate that reproductive morphometric and endocrine biomarkers in croaker are sensitive to moderate hypoxia, and are potentially useful as early warning indicators of reproductive failure.