The effects of photoperiod and water temperature on the reproductive development of black sea bass, Centropristis striata

Black sea bass are a potential candidate for marine aquaculture due to their high market value, high demand, and limited seasonal supply. One of the most significant impediments to commercial production of black sea bass is the lack of a year-round supply of eggs and larvae. Further, control of reproductive development is poorly understood in this species. Black sea bass are protogynous hermaphrodites that change sex between 2-5 years of age. It is unclear why adult black sea bass undergo sex change in the wild. Therefore, the first part of study sought to determine if density is involved in sex change. Two different densities were used (6F: 2M and 18F: 6M) in a 3:1 ratio. Sex change occurred in tanks with a greater density (5.06 g/L), while no sex change occurred in tanks with a lower density (1.66 g/L). These results suggest that density may influence sex change in this species. The second part of the first study reports the effects of various combinations of constant or changing photoperiod and water temperature on reproductive development. Females exposed to a changing water temperature and constant photoperiod (TEMPERATURE treatment) exhibited similar oocyte development and estradiol-17ss (E2) levels to females held under simulated ambient conditions (CONTROL treatment). Females exposed to both constant water temperature and photoperiod (STATIC treatment) exhibited abnormal oocyte development and low plasma E2 levels. For those females exposed to changing photoperiod and constant water temperature (PHOTOPERIOD treatment), oocyte development was normal for half of the fish and abnormal for the other half of the fish. Plasma E2 levels were low for all fish in the study. Male black sea bass exposed to the TEMPERATURE and CONTROL treatments spermiated throughout the experiment and had high levels of 11-ketotestosterone (11-KT) during breeding season. Males exposed to the STATIC and PHOTOPERIOD treatment spermiated throughout the experiment but had low plasma 11-KT levels. It appears that water temperature changes had the greatest effect on reproductive development, while STATIC conditions and changes in photoperiod led to abnormal reproductive development. A second experiment was conducted to determine if condensed winter temperature regimes could accelerate the reproductive cycle. Fish were held on a 2, 4, and 8-week treatment at 12°C. After the allotted time expired, fish were maintained at ambient water temperature (15-16°C) until spawning season commenced (April 7th), after which water temperature was brought up to 18-21°C. All fish examined on the 2, 4, and 8-week treatment changed sex. Most fish that were held on the 2-week treatment did not reach vitellogenesis before changing sex, while most fish held on the 4-week and 8-week treatments reached vitellogenesis and then underwent sex change. Levels of plasma E 2 were low for all female fish and levels of 11-KT were non-detectable in fish just beginning sex change. Histology revealed the presence of both vitellogenic oocytes and testes together, which has not previously been reported. These data suggest that a condensed winter temperature regime should not be used when trying to obtain a year-round supply of eggs and larvae