Enzymatic and Histological Evaluations of Gut and Liver in Rainbow Trout, Oncorhynchus mykiss, Fed with Rice Protein Concentrate-based Diets

This study was carried out in order to investigate the histological and biochemical responses in the gastrointestinal tract (GIT) of rainbow trout fed a rice protein concentrate (RPC). A stock of 360 juvenile rainbow trout (62.4 ± 0.3 g) were randomly distributed into 12 fiberglass tanks and fed with four experimental diets obtained by including graded levels of RPC (RPC: 0, 20, 35, and 53%) replacing fish meal on dry weight basis. The experimental plan was balanced and monofactorial, with four treatments and three replicates. At the end of the experiment, 15 fish per treatment were killed, and different tissues were sampled for biochemical and histological analyses. The results showed that total alkaline proteases were unaffected by RPC inclusion level. Amylase and lipase activities showed slight differences between the groups for all examined tracts. No histopathological changes were observed in GIT for any of the dietary treatments. Liver samples of fish fed with RPC-based diets were characterized by a slight decrease in lipid vacuolizations and a decreasing trend in the Ceroid Substances Presence Index. In conclusion, RPC did not show detrimental effects on the intestinal morphology and modification of tissue enzyme activity in rainbow trout.