Temperature and dietary carbohydrate level effects on performance and metabolic utilisation of diets in European sea bass (Dicentrarchus labrax) juveniles

This study aimed to evaluate the effect of temperature and dietary starch level on growth performance, nutrient utilisation, whole-body composition and activity of selected hepatic intermediary metabolism enzymes in European sea bass juveniles. An experimental diet was formulated to contain 46% crude protein, 12% crude lipids and 30% pregelatinized starch (diet 30GS); two other diets were formulated to include the same levels of all ingredients as diet 30GS except for the pregelatinized starch, which was included at 20% (diet 20GS) or 10% (diet 10GS). Diets were assigned to triplicate groups of 25 fish (initial weight: 15 g) at two water temperatures (18 and 25 °C) for 10 weeks. Group receiving diet 30GS was fed to apparent satiation and groups fed diets 20GS and 10GS were pair-fed according to group fed diet 30GS, so that each group ate the same amount of all nutrients except for carbohydrates. At the end of the trial, growth rate, feed efficiency and protein efficiency ratio were higher at 25 than at 18 °C. Dietary starch level did not affect growth or N utilisation. Feed efficiency was inversely related to dietary starch level. Whole-body lipids and energy content were higher at 25 °C and increased with dietary starch levels. Whole-body protein and ash content were also higher at 25 °C but were not affected by dietary starch level. Liver glycogen, HSI and VI increased with dietary starch level. ADC of starch was higher at 25 °C and within each temperature decreased with increasing dietary starch levels. ADC of protein was neither affected by temperature nor dietary starch levels. Data on enzyme activities showed that hexokinase (HK) but not glucokinase (GK) was affected by temperature. Dietary starch level affected the activities of glucokinase and glucose-6-phosphate dehydrogenase (G6PD) but not of the others enzymes tested (HK, PK, FBPase and GDH).