Exposure to Chronic Hypoxia in the Gulf of Mexico Significantly Decreases the Reproductive Potential of Male Atlantic Croaker.

Seasonal hypoxia has greatly increased in many estuaries and coastal regions such as the northern Gulf of Mexico over the past 30 years due to increased anthropogenic inputs of nutrients. The long term effects of recurring hypoxia exposure on marine ecosystems and valuable fisheries resources are unknown. Previous laboratory studies have shown that chronic exposure of male Atlantic croaker to hypoxia (dissolved O2 < 2 mg/L) resulted in 1) disruption of the endocrine system, including decreased circulating teleost progestin hormone, 17,20beta,21-trihydroxyprogesterone (20beta-S) levels; 2) a decrease in the abundance of the novel receptor on sperm plasma membranes that mediates the effects of 20beta-S, membrane progestin receptor-alpha (mPR-alpha); and 3)decreased sperm motility, an important determinant of sperm quality. We provide evidence that exposure of male Atlantic croaker to chronic hypoxia in the Gulf of Mexico in the summer of 2010 significantly altered the reproductive physiology of the fish on morphological, molecular, and functional levels. In several of the hypoxic sites surveyed, male gonadal-somatic indices (GSI) were significantly lower than the GSI of fish from the reference normoxic site. Message and protein expression levels of mPR-alpha were also significantly lower in the testes of fish with low GSIs compared to the high GSI fish at the reference sites. In addition spermatogenesis was disrupted in fish obtained from hypoxic sites. Finally, sperm motility was also significantly decreased in individuals sampled from hypoxic sites when compared to the reference site. Our findings in the Gulf of Mexico clearly indicate that environmental exposure to hypoxia disrupts male croaker's reproductive potential with possible long term population impacts. (poster)