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 (8.2±1.0 g) were randomly distributed in 12 tanks (150 L) at a density of 46 fish/ tank and fed different levels of dietary PHB (0, 0.5, 1 and 2%) for 70 days. At the end of the experiment, the results showed that PHB affected growth performance and the fish fed 0.5 and 1% PHB diets had a significant higher weight gain and specific growth rate (SGR) than the control (p<0.05). The specific activity for total protease and amylase in 1% PHB was significantly higher than that of both the control and 2% PHB (p<0.05). In addition, PHB significantly affected the muscle fatty acids profile but did not change protein and lipid content. Also, our results indicated that 1 and 2% 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 1% PHB.