Abstract:The annual ovarian maturation cycle and the variation of correlated plasma sex steroids levels were studied by employing light microscopy and morphometric methods combined with radioimmunoassay. In addition, the relationships between GSI, CF, HSI, sex steroids and temperature, photoperiod were investigated through statistical analysis. Results showed that barfin flounder features asynchronous oocyte development and batch spawnings. The oocyte growth included six phases, and six stages in ovary maturation cycle accordingly. Gonadosomatic index (GSI), hepatosomatic index (HSI) and condition factor (CF) were all found to increase prior to, or during the peak phase of vitellogenic growth corresponding to the gonad development. Statistical analysis revealed that GSI was positively correlated with CF while HSI showed negative relationship with CF. Temperature played more important role in regulating the gonad development compared with photoperiod based on the correlation analysis between GSI, temperature and photoperiod. During spawning the serum estradiol level began to increase in June (stage Ⅲ) and reached the first relatively lower peak in September and peaked in February. After the spawning, it dropped down to a relative low level and maintained until the next reproductive cycle. The testosterone level achieved the first relatively high peak in July and peaked in January, which was a month earlier than that of estradiol. A positive relationship was found between estradiol and testosterone level. Statistical analysis revealed that a positive relationship existed between photoperiod and estradiol level. In addition, the estradiol level showed positive correlations with GSI and CF. These results could highlight the reproductive cycle of captive barfin flounder females, and also serve as useful tools for broodstock breeding and determination of timing for hormone induced spawning.
