Ontogenetic changes of learning capability and stress recovery in Pacific threadfin juveniles

Time taken by Pacific threadfin Polydactylus sexfilis juveniles to learn a conditioning reward was taken as the criterion for learning capability. Fis h of 50 mm and 90 mm L-F had a better learning capability than did smaller (22 mm, 36 mm) or larger (130 mm) size classes. Larger fish (90 mm and 130 mm) were quicker to recover from handling stress than were smaller fish. Ba sed on these experiments it is suggested that 90 mm size class should have the highest adaptability when released into the wild. (C) 2000 The Fisherie s Society of the British Isles.