THE EFFECTS OF CORTISOL, STRESS AND REARING TEMPERATURE ON BLACK SEA BASS (CENTROPRISTIS STRIATA) SEX DIFFERENTIATION

Teleosts exhibit some of the most diverse array of reproductive strategies of all vertebrates, including gonochorism and hermaphroditism. Black sea bass (BSB; Centropristis striata) are protogynous hermaphrodites that undergo sex change between 2-6 years of age in the wild. Transition is initiated earlier in captivity and a greater percentage of fish differentiate directly as males. Captivity and environmental factors, such as temperature, can activate a stress response in fish that can lead to increased production of cortisol, the primary glucocorticoid released following a stressor. Cortisol treatment during sensitive developmental periods has been shown to have masculinizing effects on many teleost fishes. Previous studies examining environmental effects on sex change and differentiation in BSB found no definitive mechanisms for masculinization. Our objective was to evaluate whether stress, cortisol administration, cortisol inhibition and temperature influence BSB sex differentiation. In this effort, wild, sexually undifferentiated fish were collected from Rhode Island, housed in recirculating systems and stressed biweekly by net-chasing, fed diets supplemented with cortisol, a cortisol receptor antagonist (mifepristone), or a cortisol synthesis inhibitor (metyrapone). In a separate experiment, BSBs were raised at different water temperatures (15, 20 or 25ºC) until sexually differentiated. Long-term cortisol administration partially masculinized all female BSB but repeated acute stressors (net chasing) did not alter sex differentiation relative to the control group. Blocking cortisol receptor binding, but not cortisol synthesis, delayed sex differentiation in this species. We identified a glucocorticoid response element in the gonadal aromatase (cyp19a1a) promoter indicating a possible relationship between cortisol and cyp19a1a expression. No differences in sex ratio were observed among temperature treatments, supporting previous findings. The proportion of fish that differentiated directly as males was higher than expected for an obligate protogynous hermaphrodite, suggesting the possibility of a diandric reproductive strategy. These studies provide further understanding of sex differentiation in BSB that can provide valuable insights for future aquaculture opportunities and fisheries management