Energy requirement for maintenance and efficiency of energy utilization for growth in juvenile turbot (Psetta maxima, L.): The effect of strain and replacement of dietary fish meal by wheat gluten

Restricted ration level experiments were realized to determine the gross, digestible and metabilizable energy requirements for maintenance (GEm; DEm; MEm) and the efficiencies of energy utilization for growth (kg(GE); kg(DE); kg(ME)) in juvenile turbot. The effects of the fish strain (Denmark, DK; Iceland, IS) as well as the partial replacement of fish meal by wheat gluten in the diet were examined as possible factors affecting the energy metabolism. Turbot (initial body weight 49 g) were reared in a recirculation aquaculture system supplied with seawater at a temperature of 17 ± 0.6 °C and 26 ± 1.2 ppt salinity for 67 days. Two diets, differing in wheat gluten content (80 g or 330 g kg− 1 diet) were fed at six increasing feeding levels, from near maintenance to ad libitum levels, once a day per hand. Chemical composition and energy content of body weight gain were determined by using the comparative slaughter technique. Linear regression analyses were applied to obtain GEm, DEm, MEm, kg(GE), kg(DE) and kg(ME).GEm, DEm and MEm were 21.6–29.8, 17.0–23.5 and 15.5–21.4 kJ kg− 0.8 d− 1, respectively, and kg(GE), kg(DE) and kg(ME) were 0.46–0.49, 0.59–0.64 and 0.63–0.68, respectively. Values for GEm, DEm and MEm as well as for kg(GE), kg(DE) and kg(ME) in turbot from IS were significantly higher than in fish from DK, but without any effect on energy retention at high feeding levels. Turbot receiving the diet where fish meal was partially replaced by wheat gluten showed higher GEm, DEm and MEm as well. No effect on energy retention at high feeding levels was observed again. It is concluded that differences in energy metabolism between strains might be considered when selecting turbot for aquaculture production.

► Turbot strain affects maintenance energy requirement and energy utilization. ► Exchange of fish meal by wheat gluten increases maintenance energy requirement. ► Exchange of fish meal by wheat gluten increases energy utilization efficiency. ► Observed differences did not affect energy retention at a high feeding level. ► No growth reduction by wheat gluten up to a proportion of 33% in turbot diets