Abstract
We documented the annual ovarian maturation cycle and measured serum sex steroids levels in the spotted halibut,Verasper variegtus,using histological and morphometric methods and radioimmunoassay.In addi-tion,we analyzed the relationship between the gonadosomatic index(GSI),condition factor(CF),hepatosomatic index(HSI),sex steroid levels and temperature or photoperiod.Oocyte development was asynchronous and the halibut exhibited batch spawning behavior.We divided oocyte growth in sexually mature females into five phases.Similarly,the ovarian maturation cycle was divided into four stages.GSI,HSI,and CF all increased prior to,or during the peak phase of vitellogenic growth corresponding to gonad development.The GSI was positively corre-lated with HSI and CF.Temperature had a greater influence on gonad maturation(GSI and HSI) than photoperiod.The level of serum estradiol began to increase in November and peaked in January,thereafter decreasing to a rela-tively low level until the following reproductive cycle.The level of serum testosterone peaked in October,two months earlier than that of the peak in estradiol.We found a positive relationship between the levels of estradiol and testosterone.Both temperature and photoperiod had a significant positive effect on levels of serum estradiol,which was also positively correlated with GSI and HSI.In addition,temperature and photoperiod had a significant effect on HSI and CF,respectively.Our results provide insight into the physiological and endocrine mechanisms controlling the annual reproductive cycle of captive female spotted halibut brood.In addition,our observations provide guidance for broodstock programs and for the determining the optimal timing for hormone induced spawning.
Published Version
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