Spawning behavior and after-spawning survival in induced triploid ayu Plecoglossus altivelis

Spawning behavior and after-spawning survival of induced triploid and normal diploid ayu Plecoglossus altivelis were observed in an exrerimental stream. Female triploid did not show spawning behavior, and never came to the spawning bed. On the other hand, male triploid came to the sapwning bed and chased female diploid, and took part in spawning activity with male diploid. Survival rate of female triploid was 80% from the sapwning season to next April, being higher than the rate in female diploid. The problems of releasing triploid ayu to the natural rivers were discussed in relation with spawning behavior and after-spawning survivals.