Replacing the substitute-Guar meal as an alternative for non-genetically modified soybean meal in the nutrition of rainbow trout (Oncorhynchus mykiss, Walbaum, 1792)

Soybean meal (SBM) is widely used in aqua feed products. In the European Union, only non-genetically modified (non-GM) SBM is accepted. However, global production of non-GM soybeans is declining and is limiting its utilization in aqua feeds. Therefore, non-GM SBM alternatives are required. In this study, guar meal was evaluated as a substitute for non-GM SBM in test feeds for rainbow trout (Oncorhynchus mykiss). Fish (initial weight of 57 +/- 10.1g) were stocked to 12 experimental tanks of a freshwater recirculation system with a stocking density of 6kg/tank (500L). Fish were organized in triplicate groups and received isonitrogenous and isocaloric experimental feeds designated as control and test feeds 1-3, where 0, 50, 100 and 150g/kg feed of non-GM SBM was replaced by guar meal. During the experimental test period of 56days, fish were fed twice a day until apparent satiation. Compared to the control group, daily feed intake of test feeds 1-3 was significantly increased by guar meal inclusion. No significant differences in feed conversion ratio and specific growth rate were detected among all the treatments. Furthermore, guar meal inclusion did not affect protein efficiency ratio. However, protein productive value was significantly impaired when guar meal incorporation was above 100g/kg feed. In accordance with the affected protein productive value, the crude protein content of the proximate whole fish body declined significantly. In contrast, condition factor, hepatosomatic index, slaughter yield and fillet yield provided no significant differences between the experimental groups. In conclusion, this study demonstrated that non-GM SBM could be entirely replaced by guar meal without affecting the general performance of fish and suggests guar meal as an appropriate alternative for non-GM SBM in the nutrition of rainbow trout.