Partial Replacement of Fish Meal with Three Different Protein Sources in Rainbow Trout Oncorhynchus mykiss: Response of Intestinal Digestive Enzymes

Objective: In fish feeding formulation, high interest has recently been addressed to protein sources alternative to Fish Meal (FM); nevertheless, the response of digestive enzymes to dietary changes is not fully known. To fill this gap, a study was undertaken in rainbow trout (Oncorhynchus mykiss), to explore the effects on intestinal enzymes (trypsin, chymotrypsin, carboxypeptidases A and B, amylase) of three experimental diets, containing a plant protein source (pea protein concentrate-PPC), a microbial protein source (bacterial protein meal-BPM) or a mix of PPC and BPM (MIX), in partial (50%) replacement of FM. Methods: Two feeding regimes (apparent satiation or rationed feeding at 1.4% of the fish wet biomass) and three times (1, 3 and 24 hours) after ingestion were tested. Enzyme activities were measured using conventional biochemical methods for digestive enzymes determinations. Results: PPC administered to satiation lead to not significantly higher protein utilization than FM, as suggested by proteolytic enzymes trypsin, chymotrypsin, carboxypeptidase A. In fish fed rationed regime, PPC induced carboxypeptidase B peak and moderate trypsin increase. BPM stimulated trypsin in fish fed both feeding regimes and carboxypeptidase A in those fed to satiation. MIX diet varied significantly trypsin, carboxypeptidase B and amylase, increasing carboxypeptidase A and decreasing chymotrypsin in fish fed to satiation. Conclusions: Digestive enzyme patterns were generally unaffected by the tested protein sources, suggesting that they could partially replace FM without detrimental effects on rainbow trout digestive processes.