Abstract
As a preliminary investigation into the effects of environmental factors on gonadal development using adaptive physiological characteristics, we examined the involvement of photoperiod and water temperature in the ovarian development of the redspotted grouper, Epinephelus akaara. During October 2014 (non-breeding season), the photoperiod and water temperature were adjusted to 12L:12D and 18°C respectively. Every 3 weeks, daylight was increased as follows a 13L:11D and 14L:10D in the photo-thermal treatment group, and the control group was maintained under natural conditions. After 9 weeks, water temperature was increased to 23°C in the photo-thermal treatment group. In photo-thermal treatment group, GSI increased significantly after 9 weeks (1.36 ± 0.19) and 12 weeks (3.31 ± 0.20) compared with the control group. At 12 weeks after photo-thermal treatment, all fishes matured into ovaries containing late vitellogenic oocytes. The expression of FSH β and LHβ mRNAs also increased significantly. However, in the control group, the ovarian development was maintained at an immature stage. Based on these results, we demonstrate that exposure to long photoperiod and high water temperature can induce the sexual maturation of immature red-spotted grouper during the non-breeding season.
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