FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

This study aimed to determine the effects of temperature on gonadal development, sex change ratio and serum luteinizing hormone (LH) concentration in hermaphrodite protandrous black porgy, Acanthopagrus schlegeli. Before the breeding season (September), 2- to 3-year-old black porgy were first reared at 33 °C, then these fish were divided into four groups that were further reared at 18 °C, 23 °C, 28 °C and 33 °C at the beginning of the spawning season (December). The fish were then sacrificed at the end of the breeding season in the next year (February). The results indicated that 60% of black porgy had a sex-change to female in the control group (23 °C). In the high-temperature group (33 °C), no black porgy changed sex, while the female proportions of the other groups were 5.55% (18 °C), 5.26% (23 °C), and 25% (28 °C) after 45 days. Spermination was observed in the 18 °C, 23 °C, and control groups. In terms of histology, the gonadal development of the 33 °C -reared fish was suppressed, and only one of the fish had male function (that is, spermids were observed) during spawning season. In the other groups, the gonads of the fish had already developed into ripe ovaries or testes after 45 days of rearing, but the female ratios in these groups were obviously lower than that in the control group (60%). The serum LH concentration of the control fish surged during the prespawning (Oct. and Nov.) and spawning seasons (Feb.), but the LH surge was observed only in one fish from the 33 °C -reared group. In the 23 °C - and 28 °C -reared groups, the serum LH levels increased after 45 days of rearing. This research confirmed that high water temperature influences sex change mechanism in hermaphroditic black porgy through the inhibition of gonadal development and gonadal maturation, as well as its effects on sex change in black porgy and serum LH concentration.