Effects of Replacing Fish Meal with Soybean Meal or Fermented and Phytase-Treated Soybean Meal Respectively, on Growth Performance, Feed Utilization, and Apparent Digestibility in Juvenile Turbot (Scophthalmus maximus L.)

The objective of this study was to evaluate the effect of fish meal (FM) substitution with gradient soybean meal (SBM) or fermented and phytase-treated soybean meal (PHSBM) in the diets of turbot (Scophthalmus maximus). A 9 week feeding trial was conducted using juvenile turbots (Scophthalmus maxima) fed seven experimental diets. The seven isonitrogenous (approximately 50% crude protein) and isoenergetic (approximately 21.0 kJ/g diet of gross energy) diets were formulated to include FM protein substitution with corresponding amounts of protein from soybean meal and phytase-treated soybean meal sources. Results showed that survival rate and feed intake did not differ significantly between the FM diet and any plant protein incorporated diets. Compared with the FM diet, final body weight and SGR were significantly reduced by the SBM2, SBM3, and PHSBM3 diets. Except for the PHSBM1 diet, feed efficiency ratio in the other SBM or PHSBM incorporated diets was much lower than in the FM diet. Body ash content was not affected by gradient PHSBM incorporated diets compared with the FM diet, while SBM incorporated diets (SBM2 and SBM3) showed a higher ash content than the FM diet (P<0.05). Body crude protein was significantly reduced when fishmeal protein was replaced by soybean meal up to 60% (SBM3). There was no significant difference in the crude lipid and moisture contents among different treatments. Fish meal replaced by gradient PHSBM did not affect the apparent digestibility coefficients (ADC) of dry matter and crude protein, while the ADC of dry matter was markedly reduced in all the soybean meal incorporated diets compared with the FM diet. These results show that 30% fish meal protein could be replaced by soybean meal in the diet of turbot, while PHSBM could be substituted for up to 45% dietary fish meal.