Immunostimulatory and growth-promoting potential of poly-β-hydroxybutyrate in rainbow trout (Oncorhynchus mykiss) fingerlings culture

In the current study, the effect of dietary supplementation of poly-β-hydroxybutyrate (PHB) on growth performance, digestive enzymes activity, body composition, non-specific immune response and diseases resistance of rainbow trout fingerlings were investigated. Five hundred and fifty-two healthy fingerlings (۸.۲±۱.۰ g) were randomly distributed in ۱۲ tanks (۱۵۰ L) at a density of ۴۶ fish/ tank and fed different levels of dietary PHB (۰, ۰.۵, ۱ and ۲%) for ۷۰ days. At the end of the experiment, the results showed that PHB affected growth performance and the fish fed ۰.۵ and ۱% PHB diets had a significant higher weight gain and specific growth rate (SGR) than the control (p<۰.۰۵). The specific activity for total protease and amylase in ۱% PHB was significantly higher than that of both the control and ۲% PHB (p<۰.۰۵). In addition, PHB significantly affected the muscle fatty acids profile but did not change protein and lipid content. Also, our results indicated that ۱ and ۲% PHB markedly decreased cumulative mortality of the fingerlings challenged by Yersinia ruckeri infection. Overall, the results of this experiment revealed that PHB acts as a growth promoter and immunostimulator in rainbow trout fingerlings and the optimal PHB level in trout diet was estimated at ۱% PHB.

Keywords:

Poly-β-hydroxybutyrate , Growth promoter , Rainbow trout , Immune response , Yersinia ruckeri