Use of soybean meal as a substitute for fish meal in a newly developed soft-dry pellet for yellowtail

The availability of defatted soybean meal (SBM) as a substitute for fish meal (FM) in a newly developed soft-dry pellet (SDP) was evaluated by feeding SDP containing 0-50% SBM to both juvenile and adult yellowtail. Palatability or acceptability of the experimental SDP was not influenced by the inclusion of SBM up to 50%. Growth and feed gain ratio were highest in both sizes of fish fed on the control FM diet but decreased corresponding to the elevation of SBM levels. This might be due to the reduced levels of protein and energy in the SBM diets resulting from the difference in protein and lipid contents between FM and SBM, as the diets were not iso-nitrogenous and iso-caloric. This was also supported by the result that the weight gain per digestible energy or protein intake did not differ greatly among the experimental groups. A diet with 25 % SBM and 15% corn gluten meal (CGM) showed better feed performances than the 40% SBM diet, suggesting the availability of CGM as a protein source in combination with SBM. These results together with hemochemical assessments and rheological properties have shown that SBM can be included as a protein source up to 30% in place of FM in SDP for yellowtail without any adverse effects.