The effects of stocking density on the production and health of olive flounder ( <scp> <i>Paralichthys olivaceus</i> </scp> ) in <scp>RAS</scp>

Abstract Olive flounder ( Paralichthys olivaceus ) is known for its growth performance in aquaculture. Fish are typically raised at high densities in recirculating aquaculture systems (RAS), which may impact animal health. Flounder (55.2 ± 16.3 g) were stocked at three densities: a low density (LD) of 3 kg/m 2 , medium density (MD) of 6 kg/m 2 , and high density (HD) of 9 kg/m 2 in 1.2 m 2 tanks. Each treatment contained three replicate tanks, all of which shared a common sump and filtration system. Stress indicators, including serum cortisol, glucose, growth hormone (GH), and insulin‐like growth factor‐1 (IGF‐1) levels, were analyzed. At the end of the 93‐day experiment, individual weight was significantly higher in LD, followed by MD and HD, and survival was over 95% in all treatments. There was significantly greater biomass in HD, followed by MD and LD. No significant differences were found in GH and IGF‐1 levels. However, glucose concentration was significantly higher in HD fish on day 30 and LD on day 93; cortisol levels were significantly lower in MD on day 30 and HD on day 61. Results suggest that olive flounder can be grown at a density of 55 kg/m 2 with little impact on health. However, a tradeoff exists between density and individual performance. This species seems well suited for RAS, although further research under commercial conditions is necessary.