First evidence on the growth of hatchery-reared juvenile meagre Argyrosomus regius released in the Balearic Islands coastal region

Abstract

Abstract The success of restocking (releasing hatchery-reared juveniles in the wild) depends on the capacity of phenotypes that are already adapted to captivity to readapt to the natural environment. Changes in growth rate after release can be monitored to determine whether released fish are adapting well to the natural environment or failing to adjust to wild conditions. Nevertheless, it is not known whether released individual fish experience a shift in growth rate. Alternatively, the fish showing long-term survival could be those that were already larger before release. This question is relevant for the maximization of stocking success because certain phenotypes (those with a better probability of readapting) could be selected for release. This study compared the somatic growth of released and recaptured meagre, Argyrosomus regius , with control (captive) meagre belonging to the same cohort. Recaptures that had spent less than 3 months at liberty showed the same length-at-age as the control fish, but the length-at-age of many recaptured fish that had spent more than 3 months at liberty was greater than expected. The otolith radius of the growth mark corresponding to the first year of life (i.e., when all fish were still in captivity) was significantly greater for fish that had spent more than 3 months at liberty, indicating that these meagre were larger and had a higher growth rate when they were released. Moreover, the analysis of daily otolith growth before and after release showed that most of the recaptured meagre that had spent less than 3 months at liberty grew an equal or lesser amount in the wild than before release. In contrast, most of the recaptures that had spent more than 3 months at liberty showed a higher growth rate after release. Therefore, results are discussed in light of the combined effect of differential survival and increased growth, although the low sample size requires interpreting the results carefully.