Abstract
The seedlings for stock enhancement are required to have adequate behavioral characteristics (fish quality), which enable them to adapt to the natural environment after release. Screening of index behaviors, which reflect fish quality, should be an important approach. In this point of view, we have been investigating aggressive behavior in the seedlings of yellowtail (Seriola quinqueradiata) and Japanese flounder (Paralichthys olivaceus), because aggressive behavior has an important role for the survival in the early life stages of these 2 species. We found typical shivering behaviors in the metamorphosing larvae and named them J-posture in yellowtail and Ω-posture in Japanese flounder, respectively. Both postures were significantly and positively related to aggression in the juvenile stage, and we can predict which larva will become an aggressive juvenile. We propose that these postures will be applicable for future index of fish quality for release.
