Releasing of the European sea bass Dicentrarchus labrax (Linnaeus) in the Adriatic Sea: Large-volume versus intensively cultured juveniles

Themain goals of this projectwere to evaluate if artificial reefs are suitable sites for releasing hatchery-reared sea bass and if intensively and extensive large-volume cultured sea bass are suitable to be released into the wild for stock enhancement purposes. Large-volumecultured basswere reared in lower densities compared to intensively cultured ones and, when fry were about 90 days old, were transferred into external ponds connected to the channels of the surrounding marsh,where that they could integrate pellet food sourceswith live prey. Intensively cultured bass were fed for 55 dayswith Artemia salina (Linnaeus, 1758) and thenwith pellets. Underwater visual census (UVC) and fishing samplingwere carried out to verify the presence of the tagged specimens at the artificial reef. A lowmortality rate after tagging was observed and good tag retention was recorded. Individuals dead after tagging were statistically smaller than survivors. A total of 45 tagged bass (42 large-volume and 3 intensively cultured) were returned by fishers and 16 specimens were observed during UVC (15 large-volume and 1 intensively cultured). The majority of recaptured bass concentrated in the surroundings of river mouths and harbours suggesting that, after release, sea bass migrated towards shallower and brackishwaters. Subsequently, as they grew, they came back towards deeperwaters and tended to aggregate around artificial structures. Analysis of stomach contents of returned individuals confirmed their dependence on hard-substrate food items. The study provides evidence to support the suitability of large-volume juveniles for restocking purposes, due to their ability to prey on wild food and their endurance to the stress caused by release operations.