Environmental control of gonadal development in the tropical damselfish Chrysiptera cyanea

Photoperiod and temperature are potent environmental factors regulating the reproductive cycle of temperate fish. It is unclear whether fish in the tropics utilize these environmental factors for initiation and termination of their reproductive activity. The aim of this study was to examine the involvement of photoperiod and temperature in ovarian development of sapphire devil, Chrysiptera cyanea, which is a reef-associated tropical damselfish. Monthly collections of individuals in the experimental region (26 degrees 42'N, 127 degrees 52'E) revealed an increase in the gonadosomatic index (GSI) and appearance of vitellogenic oocytes in ovaries from March to August. Post-ovulated follicles and yolk-laden oocytes coexisted in some ovaries from May to August. These results suggest that the sapphire devil in this region has a restricted reproductive season with repeated spawnings. Rearing the fish during the resting phase (December) under experimental conditions of a long photoperiod (LD 14:10) at 31 degrees C for 15 days and at 25 or 31 degrees C for 60 days resulted in a significant increase in GSI and induction of vitellogenic oocytes, whereas a short photoperiod (LD 10:14) at the same temperatures failed to induce oocytes at the yolk stages. Long-term rearing of the fish at 31 degrees C caused regression of vitellogenic oocytes. During the reproductive season, the fish reared at 25 degrees C had higher spawning frequency than those at 20 and 30 degrees C. It is concluded that photoperiod and temperature are involved in the regulation of gonadal development and a long photoperiod within a suitable range of water temperatures is required for continuity of reproductive activities.