Abstract
The present study examined the potential to induce spontaneous spawning in cultured barfin flounder using increased temperature as a stimulus; that is, increasing the rearing temperature from 6 to 8-9°C over 6 h in the morning and reducing it to 6°C the following morning. In 1997 and 1998, cultured barfin flounder, aged 3 years, were reared under two water temperature regimens. In the brood stock groups reared at fixed temperatures (6 or 8-9°C) during the spawning season, all females ovulated normally and released eggs into the aquarium; however, almost all eggs were unfertilized. In contrast, in groups reared with periodic stimulation with increased temperature, the number of eggs collected per day was greater than that from groups without stimulation. Furthermore, fertilization was induced frequently throughout the experimental term and the number of fertilized eggs obtained was much greater. Estimation of fertilization time indicated that fertilization occurred largely within 24 h after the stimulation was conducted. Moreover, in 2000, the fertilization rate of fish reared with periodic stimulation was very much higher than that in fish without stimulation. These results demonstrate that performing periodic increased temperature stimulation during the spawning season is effective in accelerating egg release in females and also in inducing fertilization of cultured barfin flounder in rearing conditions.
