Dietary effects of poly--hydroxybutyrate on the growth performance, digestive enzyme activity, body composition, mineral uptake and bacterial challenge of rainbow trout fry (Oncorhynchus mykiss)

This study investigated the effects of diet supplementation with poly-beta-hydroxybutyrate (PHB) on growth performance, digestive enzyme activity, lipid metabolism, mineral uptake and bacterial challenge of the rainbow trout fry (initial weight: 111.3 +/- 13.7 mg) during a 6-week experimental period. In the experimental set-up, the commercial diet of rainbow trout fry was replaced with 0.5%, 1% and 2% PHB. The results of our work showed that the replacing of diets with PHB in experimental treatments decreases the weight of rainbow trout fry during the first 2 weeks before significantly increasing final weight at the end of the 6-week period. PHB also improved digestive enzyme activity in experimental treatments. The highest total protease, pepsin activity and pancreatic enzyme secretion were observed with the 0.5% PHB treatment. A higher concentration of Na and K was observed in the whole body of the fry fed on 1% and 2% PHB-supplemented diets. Enhanced survival rates occurred in all groups of fry after bath exposure to Yersinia ruckeri compared to rates in those fed the control diet. Our results suggest that the diet supplemented with PHB may improve growth performance, digestive enzyme activity and the functioning of the immune system. These positive effects could be considered for new applications in aquaculture.