Dietary Carbohydrate Utilization by European Sea Bass (Dicentrarchus labrax L.) and Gilthead Sea Bream (Sparus aurata L.) Juveniles

European sea bass and gilthead sea bream are two major marine finfish species reared in the Mediterranean region. Feeds for these species have high protein levels, usually supplied by fish meal. Research on alternatives to fish meal is mainly focused on plant protein feedstuffs, which are generally high in carbohydrates. Therefore, understanding the potential use of dietary carbohydrate is crucial for better utilization of such feedstuffs in the diets for these species. Factors that affect carbohydrate digestibility, metabolic utilization, as well as regulation of glucose metabolism are discussed. Data show that to ensure high digestibility, growth, and feed utilization, diets for these species should include around 20% digestible carbohydrate. Digestibility of native starch is high (above 70%) in both species, and it is further improved by processing starches (above 90%). Regarding carbohydrate complexity, it appears that European sea bass perform better with starch than glucose, while the opposite is true for gilthead sea bream. An enhancement in the activity of key enzymes of the glycolytic pathway and an increase of liver glycogen content is generally observed in the two species after feeding carbohydrates. An inverse regulation of the gluconeogenic enzyme activities with dietary carbohydrate intake is not observed in either species.