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.