Effects of Water Temperature and Photoperiod on the Beginning of Spawning Season in the Orange-red Type Medaka : Reproductive Biology

概要

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Rearing experiments were conducted to study effects of photoperiod and water temperature on the beginning of spawning season in the orange-red type medaka, Oryzias latipes. Fish, cultured in Tokyo and ready for rapid gonadal growth in spring, was transferred to 7 conditions (16℃ 14L, 14℃ 14L, 14℃ 12L, 14℃ 10L, 12℃ 14L, 10℃ 14L, 8℃ 14L), and reared for 4 to 8 weeks. Changes in gonadosomatic index (GSI) and gonadal histology were examined. Groups at 14 and 16℃ showed rapid GSI increase irrespective of photoperiod. Active yolk globule accumulation and spermatogenesis began, and spawning was observed in these groups. After 8 weeks, many regressive oocytes were noticeable in 14℃ groups. In groups at temperature below 14℃. GSIs of both sexes remained low and spawning was not observable. But yolk globule accumulation proceeded slowly in 10 and 12℃ groups. When medaka in early spring were transferred to 4 conditions (16℃ 10L, 8L 6L 4L) and reared for 4 weeks, they could mature and spawn in all experimental regimes, which eliminates possibility for photoperiodic response in spring. From these results, it is clear that temperature rise in spring only is responsible for the beginning of spawning season in medaka cultured around Tokyo.
社団法人日本動物学会の論文
1988-10-15