Performance of rainbow trout (Oncorhynchus mykiss) fingerlings fed diets containing different levels of faba bean (Vicia faba) meal

• Effect of substituting soybean meal with faba bean meal in Oncorhynchus mykiss diet.
• Rainbow trout fingerlings can tolerate up to 30% faba bean meal in diet
• Maximum growth performance was found at the 15% faba bean meal in diet.

This study was conducted to determine the replacement value of faba bean meal (FBM) for soybean meal (SBM) in practical diets of Oncorhynchus mykiss fingerlings. Four isonitrogenous (42% crude protein) and isolipidic (20% total lipid) diets were formulated using commercial ingredients. Faba bean meal was added in the diets at levels of 0% (control) and 15, 30 and 45%. When the FBM content was increased in the diets, the soybean meal, fish meal and wheat flour were gradually reduced to adjust protein and carbohydrate contents. A completely randomized experimental design was developed with four treatments and three replicates. Two hundred and forty rainbow trouts with average initial weight of 12.5 ± 0.09 g were assigned to twelve experimental tanks. The experiment lasted for seven weeks. Based on results, survival did not differ among treatments (p > 0.05). Growth performance and feed conversion ratio of rainbow trout fingerlings fed diets containing 15 and 30% FBM were similar (p > 0.05) to the control diet. However, 15% FBM diet showed better performance (p < 0.05) compared to the 30% FBM diet. The poorest growth performance and FCR were observed in the fish fed the diet containing 45% FBM. The apparent digestibility of dry matter and protein decreased with increasing levels of FBM from 30% to 45% in diet. No significant difference (p > 0.05) was found in carcass protein and ash contents among the dietary treatments. The present results demonstrated that rainbow trout fingerlings can tolerate up to 30% FBM in diet, but maximum growth performance was found at the 15% FBM diet.