Predation differences between wild and hatchery-reared tiger puffer Takifugu rubripes juveniles in a salt pond mesocosm

To compare the eŠects of predation on the post-release mortality of wild and hatchery-reared juveniles of the tiger puŠer Takifugu rubripes we conducted release experiments in a semi-natural environment using a salt pond mesocosm (5,300 m2). We released hatchery-reared juveniles together with wild juveniles into a pond with predators. Survival of the hatchery-reared juveniles (56.0) was signiˆcantly lower than that of the wild juveniles (86.0). These results indicate that predation is a major cause of post-release mortality of this species. We also compared swimming depths of wild and hatchery-reared juveniles immediately after release into an experimental tank (33.5 cm in depth). Wild juveniles swam near the tank bottom and showed bottom-dwelling behavior, but hatchery-reared juveniles swam mostly in the water column. Similar behavioral diŠerences were observed in release experiments in a mesocosm. We also compared body compositions of tetrodotoxin (TTX), which was detectable in the wild juveniles, but hatchery-reared juveniles had no detectable TTX. We concluded that predation shortly after release and behavioral defects in hatchery-reared juveniles, such as changes in swimming behavior and feeding behavior, might be among the main causes of mortality in the stock enhancement program of this species.

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