Replacement of fish meal with various types of soybean products in diets for the Asian seabass, Lates calcarifer

Abstract

The effect of partially replacing fish meal in seabass diets with different soybean meal (SBM) products on the growth and apparent protein digestibility was studied. Five isonitrogenous and isocaloric diets were formulated to contain all fish meal (control diet), 21.0% solvent extracted SBM, 27% extruded full-fat SBM, 28.5% steamed full-fat SBM and 27.5% soaked raw full-fat SBM as substitutes for 15% fish meal in the control diet. Each diet was fed to three replicate groups of juvenile seabass with an average initial weight of 1.26–1.37 g over a period of 10 weeks. The fish were contained in flow-through and aerated aquaria. Fish fed the control diet grew significantly better than fish fed extruded full-fat SBM, steamed full-fat SBM or soaked raw full-fat SBM diets, but not significantly different from that of fish fed the solvent-extracted SBM diet. Feed efficiency and survival did not differ significantly among treatments except for fish fed the soaked raw full-fat SBM diet. Fish fed the soaked raw full-fat SBM had significantly lower weight gain, feed efficiency, protein efficiency and survival. Fish fed this diet also showed some histological changes in their gastrointestinal tract. The apparent protein digestibility of diets containing all fish meal, solvent-extracted, extruded, steamed and soaked raw full-fat SBMs were 92.8, 94.2, 92.3, 94.4 and 73.7%, respectively. The lower growth obtained in fish fed the extruded or steamed full-fat SBM diets as compared to that of the control fish meal diet could not be attributed to protein digestibility, but it could be due to the lower feed intake during the first two weeks suggesting that palatability was possibly a factor. Soaked raw full-fat SBM is a poor protein source for seabass diet. Solvent-extracted SBM is more palatable for small seabass (1.30–3.50 g) than extruded or steamed full-fat SBM. Thus, this study suggests that, if palatability of the diet can be improved, 37.5% of protein from fish meal or 15% fish meal in diet for seabass can be replaced by solvent-extracted SBM, extruded full-fat SBM or steamed full-fat SBM.