Effects of partial replacement of fish meal by soybean meal in sharpsnout seabream (Diplodus puntazzo) diet

We have studied the possible use of soybean meal (SM) in sharpsnout seabream diets by progressively increasing its inclusion level (0%, 20%, 40% and 60%) at the expense of fish meal in isonitrogenous (45%) and isoenergetic formulated (20 MJ/kg) diets. Fish of two different sizes (48 g and 195 g of initial weight) were kept in seawater tanks (26 °C on average) and fed to satiety until they reached a weight of 118 g and 340 g, after 64 and 91 days respectively. Feed consumption increased along with the soybean meal content of the diet, the differences becoming statistically significant in smaller animals as from 40% of inclusion. In larger animals, the diet containing the highest level of soybean meal produced the lowest final weight. As the soybean meal content increased, feeding efficiency and protein utilization of the diet decreased, an effect probably due to the smaller digestibility coefficient observed for these diets. Based on the results of the sensory test, flesh quality was very little affected, albeit fish feeding on diets with partial replacement of fish meal tended to be somewhat softer. Despite extending the fattening period required to reach the same final weight, the economic analysis indicates that inclusion of soybean meal in the diet reduces feeding costs.