Effect of dietary inclusion of Pyropia yezoensis extract on biochemical and immune responses of olive flounder Paralichthys olivaceus

This study was aimed to investigate the effect of dietary inclusion of autoclaved water extract from Pyropia yezoensis on growth performance, and biochemical and immune responses in olive flounder Paralichthys olivaceus. Five fish meal-based diets were prepared by adding lyophilized P. yezoensis extract (PE) at the concentration of 0, 5, 10, 15, and 20 g kg− 1 diet (designated as PE0, PE5, PE10, PE15, and PE20, respectively). One of five experimental diets was fed to experimental fish. After 9 weeks of the feeding trial, weight gain and feed efficiency of the fish fed diets containing PE extract showed an increasing trend of better performance except for those fed PE20. Insulin-like growth factor-I was also increased in a dose dependent manner in those fed diet containing PE. Lipid level in the muscle and liver showed an increasing trend as dietary PE level was increased. Especially, polyunsaturated fatty acid (PUFA) including C18:3n − 3, C20:4n − 6, and C22:6n − 3 in those muscles was significantly increased compared to control. Lysozyme activity in the plasma and kidney was increased in the fish fed PE5, PE10 and PE15, while interleukin-4 and -6 proteins were elevated only in the fish fed PE20 compared to control. During the 20 day-long challenge test with Streptococcus iniae, a cumulative mortality of infected flounder showed the highest mortality (90%) in control, whereas no mortality was observed in those fed PE15. The current study confirms earlier findings that feeding diet containing seaweed extract can induce enhancement of growth performances, immunity, and increase PUFA level in olive flounder.