Use of defatted soybean meal as a substitute for fish meal in diets of Japanese flounder ( Paralichthys olivaceus)

Abstract

Feeding experiments were conducted to examine the potential use of defatted soybean meal (SBM) in combinations with blood meal (BM), corn gluten meal (CGM), and freeze-dried meat of blue mussel as a partial replacement of fish meal in the diet of Japanese flounder. Juvenile fish of about 5 g in initial body weight were fed diets to satiation twice daily, 6 days per week for 8 weeks at 20°C. The control diet contained 75% fish meal as the protein source, while 35 or 45% fish meal was replaced with other sources of protein in the experimental diets (replacing approximately 45 or 55% of fish meal protein in the control); 25, 30, or 40% SBM, 10% BM or CGM, and 5% freeze-dried meat of blue mussel. Diets containing 25% SBM in combination with BM or CGM and the blue mussel (replace 47 or 44% of fish meal protein) resulted in best growth and feed utilization among all dietary groups tested. The final body weight, weight gain, and protein efficiency ratio in these dietary groups were higher than those for the control ( P<0.05). The weight gain of fish fed diets containing 40% SBM (replace 43%), and 30% SBM in combination with 10% BM or CGM (replace 47 or 45%), were comparable to that of the control, however, feed efficiency and protein efficiency ratio were significantly lower except that feed efficiency for the 30% SBM and 10% BM diet ( P<0.05). Diets containing 40% SBM and 10% BM or CGM (replace 59 or 57%) showed inferior growth and feed utilization compared to the control ( P<0.05). There were no marked differences in hematological characteristics together with proximate composition of the whole body of cultured fish fed the dietary treatments. These results indicate that about 45% of fish meal protein can be replaced with SBM in combination with other protein sources in the diet of juvenile Japanese flounder.