Relation of size at release of hatchery-reared black rockfish Sebastes inermis to survival in a Zostera belt around Ikuno Island, Hiroshima Prefecture, Japan

Abstract

To enhance the stock of black rockfish, Sebastes inermis, 2 cm-, 3 cm- and 5 cm-size groups of hatchery-reared fish were released in a Zostera belt around Ikuno Island after marking with ALC and fin cut. The larger the size, the farther from the release point they were recaptured and the better the survival rate. Especially, most of the 2 cm-size fish had disappeared about one month later. A predation test in a terrestrial tank confirmed that the redfin velvetfish Hypodytes rubripinnis was a dominant species as a predator at the release point, and significantly preyed on the 2 cm-size group more than the 3 cm-size group. According to changes of triglycerides in the muscle of 2 cm-and 5 cm-size groups after release, it took about one month for released fish to acclimate to the natural conditions. These results indicate that the fish size needs to be larger than 3 cm for the stock enhancement of this species in this area.