Effect of dietary chitin on growth performance, nutrient utilization, and metabolic response in rainbow trout (Oncorhynchus mykiss)

The dietary inclusion of ingredients containing chitin has been claimed to be beneficial to fish health. However, controversial results on growth performance and nutrient digestibility have been reported in literature. The present study aimed at assessing the response of rainbow trout (Oncorhynchus mykiss) fed with increasing levels of chitin (0, 1.5, 3.0, and 4.5 %) in a semi-purified basal diet. Protein and lipid digestibility was assessed and after 10 weeks of feeding, 6 h after the last meal, fish were euthanized for the evaluation of growth performance, blood biochemistry, brush border membrane and chitinolytic enzyme activity, gene expression of enzymes and nutrient transporters as well as the major pro-inflammatory intestinal cytokines, and mid intestine microbiota. Dietary chitin inclusion of up to 3 % did not hamper growth performances, nutrient apparent digestibility, and levels of most blood enzymes and metabolites. Diet including 4.5 % chitin negatively affected growth performances and nutrient digestibility. The application of a multidisciplinary approach highlighted that the biomarkers related to gut digestion functionality and inflammation response were altered also in fish fed the diets including 1.5 and 3 % of chitin, while gut microbiota did not differ between dietary treatments, even if some taxa suggested to be important in fish physiology were not recovered. Overall, the results demonstrate a good tolerance of rainbow trout to diets including chitin up to 3 %.