Soybean meal as a protein source in gilthead sea bream (Sparus aurata L.) diets: effects on growth and nutrient utilization

Abstract

[EN] The value of defatted soybean meal as a protein source for sea bream ¢ngerlings (15.2 4.4 g on average) growing to market size (300^350 g) was evaluated by feeding extruded isonitrogenous and isoenergetic diets (46% protein and 22 MJ kg 1 ) containing 20%, 30%, 40% and 50% soybean meal considering two phases. On day 87, the ¢sh weight ranged between 66 and 81g. The speci¢c growth rate (SGR) of sea bream fed 50% soybean was lower (1.73% day 1 ) than that of ¢sh fed 20% (1.87% day 1 ) and 30% (1.93% day 1 ), but the food conversion ratio (FCR) was not signi¢cantly a¡ected, and a quadratic signi¢cant trend was observed for the feed intake (FI) in relation to the dietary soybean level. At the end of the second phase on day 309, ¢sh weight was between 303 and 349 g, but SGR and FCR were similar for all diets, and ranged between 0.64 and 0.69% day 1 , and 1.95 and 2.10% day 1 respectively. The ¢nal biometric parameters were not a¡ected by the diets, although the levels of some free amino acids in the muscle were a¡ected. Sensory di¡erences were detected by panellists in ¢sh fed diet 20% as compared those fed diet 50%, which had a less marine £avour and was less juicy. The global growth results suggest the possibility of feeding sea bream weighing less than 80 g with 30% soybean meal, and for ¢sh weighing more than 80 g, a 50% dietary soybean meal can be used until the ¢sh reach commercial weight, with no negative e¡ects on growth or feed e⁄ciency. Nevertheless, when sensory analysis and economic aspects are considered, the maximum inclusion level of soybean was 20^22%.