Water temperature does not affect protein sparing by dietary carbohydrate in Senegalese sole (Solea senegalensis) juveniles

The effect of dietary protein reduction balanced by an increase in carbohydrate (starch) level on growth performance, feed utilization and intermediary metabolism of Senegalese sole juveniles was evaluated at two temperatures, 12 and 18 degrees C. For that purpose two isolipidic (16% lipids) diets were formulated to contain 550gkg(-1) protein and 90gkg(-1) starch (diet HP:LC), and 450gkg(-1) protein and 200gkg(-1) starch (diet LP:HC). Each experimental diet was fed to triplicate groups of 20 fish (initial body weight: 15.9g) within each temperature. Diets had no effect on growth and feed utilization. Temperature affected growth but not feed efficiency, with fish growing more at 18 degrees C. Fatty acid synthetase and glutamate dehydrogenase activities were higher at 12 degrees C than at 18 degrees C while activity of the other measured enzymes was not affected by water temperature. Glucokinase and malic enzyme activities were lower while fructose 1,6-bisphosphatase activity was higher in fish fed the HP:LC diet. Our data suggest that protein can be reduced from 550gkg(-1) to 450gkg(-1) by increasing starch level in high lipid diets for Senegalese sole juveniles without affecting overall performance. A reduction in protein content through an increase in dietary starch decreases hepatic gluconeogenesis. Increasing temperature from 12 degrees C to 18 degrees C improves fish growth but does not affect feed efficiency.