Momoshima Station, National Center for Stock Enhancement, Fisheries Research Agency, Onomichi, Hiroshima 722-0061, Japan
To investigate the effect of predation on the post-release mortality of hatchery-reared juveniles of the ocellate puffer Takifugu rubripes, we reared fish in an experimental salt pond (5,300 m2) with or without predators. The pond was divided into halves, one with 30 sea bass, Lateolabrax sp. (30 cm in mean total length), which is an experimental section, the other (control section) with no predators. Three hundred juveniles (mean standard length, 30 mm) were released into each section of the pond. The survival rate of the juveniles decreased remarkably in the presence of the bass, indicating that predation immediately after release is an important mortality factor. The size of the juveniles and the degree of loss of caudal fin at the time of release showed no influence on growth of juveniles after release or on their survival.