Evaluation of different dietary protein sources on tissue growth and metabolism of rainbow trout (Oncorhynchus mykiss) using nitrogen stable isotope analysis

The increased price and limited supply of fish meal (FM) have become constraints for the sustainable development of aquaculture. In the present study, soybean meal (SBM) and meat and bone meal (MBM), as alternative protein sources, were mixed (1:1) to replace 0%, 10%, 30% and 50% of the FM formulating four isonitrogenous and isoenergetic diets (i.e. FM500, FM450, FM350 and FM250). An 84-day feeding experiment was conducted to assess the nutritional contribution of each protein source to the growth of rainbow trout (Oncorhynchus mykiss) juveniles using stable isotopic analysis. At the end of the experiment, no significant growth difference was observed amongst individuals fed the FM500 and FM450 diets, whereas growth was repressed in the FM350 and FM250 groups. Isotopic fractionation amongst the different groups ranged from 0.38% to 4.61 parts per thousand and was negatively correlated with the delta N-15 values of the diets. More importantly, the nutritional contribution of the SBM and MBM components was significantly higher in the FM450 group than expected. This study demonstrates that a mixture of SBM and MBM replacing 10% dietary FM could be an effective diet formulation strategy for rainbow trout culture.