Utilization of Soybean Meal as Protein Source in Diets for Rainbow Trout.

Abstract

In order to study the utilization of defatted soybean meal (SBM) and its extruded meal (ExSBM) as a partial replacement for white fish meal (WFM), they were used to substitute WFM at levels of 30, 40, 50% in diets. A combination of 25% SBM and 15% corn gluten meal (CGM) substituting WFM of 40% in the diet was also tried. Each diet was fed ad libitum to duplicate groups of rainbow trout Oncorhynchus mykiss (12.1g on average) for 7 weeks at 12±2°C. The SBM-CGM diet produced the best performance. The growth of fish on other diets was almost inversely related to dietary SBM or ExSBM levels, probably due to the lower protein and energy intake. However, the growth rate per protein intake in these groups was almost com-parable to that of the control group. There was no marked difference in growth and feed efficiency between the SBM and ExSBM groups, except at a 50% level where there was improved growth due to an enhanced feed intake of the extruded product. Apparent digestibility of dietary protein in all cases was as high as 90-94%, irrespective of inclusion of SBM or ExSBM; but these values of starch decreased in relation to both ingredients, leading to reduced energy digestibility. Thus, for effective utilization of SBM, a combination with CGM was found to be better, reducing WFM up to 40% in the diet (replacing 63% of WFM).