Reproductive cycle in female Waigieu seaperch (Psammoperca waigiensis) reared under different salinity levels and the effects of dopamine antagonist on steroid hormone levels

摘要

Waigieu seaperch (Psammoperca waigiensis) is a tropical marine finfish species, which may inhabit wide range of salinity during the entire life cycle. Regardless of the wide salinity tolerance, little is known about how salinity may influence the reproductive endocrinology of this important tropical species. In the present study, we investigated the seasonal variations in steroid hormone levels, oocyte maturation (OM) and ovulation in fish reared under different salinity levels. In addition, we investigated the effects a dopamine antagonist (domperidone: DOM) during the peak spawning period. Mature brood fish at 3 years old were cultured in four different salinities of 5,10, 20 and 30‰ (part per thousand, ppt) from March to December 2007. Blood samples were collected monthly and key steroid hormones (testosterone (T), 11-ketotestosterone (11-KT), 17β-estradiol (E2) and progesterone (P)) levels in female fish plasma were analyzed using enzyme immu-noassay method. OM, ovulation and several reproductive performance indexes were evaluated twice per month during the breeding season. Plasma hormone analysis showed significant differences in fish groups cultured in different salinities during the seasonal cycle. The gonadosomatic index (GSI) gradually increased from March, peaking in July at 10 and 30‰, and then decreased thereafter until December. Plasma steroid levels (E2, T, 11 -KT and P) were observed in variable concentrations during the spawning period and showed monthly fluctuations that were apparently salinity dependent during on and off-seasons. Interestingly, 11-KT levels were found in small amounts in female fish and peaked in September at salinities of 10 and 20‰. DOM exposure produced significant differences in steroid hormone levels that were apparently dependent on dose, exposure time and the individual hormone. The present study indicated that holding Waigieu seaperch brood fish in different salinities during the breeding season produced significant effects on gonadal development and spawning incidences. The first spawning was observed on 8th of April for all groups after 100% water exchange at night. No significant differences of absolute and relative fecundity were observed between groups. Fish held at 10 ppt salinity during the breeding season spawned naturally, but maturity and spawning rates were reduced and no hatching was observed at the same salinity. Fish holding at 5‰ resulted to 100% mortality in brood fish. This indicated that salinity limits for oocyte maturation or ovulation and subsequent reduction in spawning, but embryonic development requires a higher salinity. The effect of salinity on embryo development and hatching rate suggests that in breeding season the brood fish spawned in areas where the salinity and other parameters are favorable.