Summary:
A dietary study was undertaken to test the effect of different protein and lipid levels in feed for turbot, Scophthalmus maximus (Rafinesque, 1810) in the grow-out phase (initial size 580 g). The experimental diets were formulated to contain 35 (LP), 42.5 (MP) and 50 (HP) % crude protein (CP), protein with a subsequent level of 15 (LL) and 25 (HL) % crude lipid (CL) for each protein level. Final weights and specific growth rates were significantly affected by the dietary treatments. Fish fed the low protein low lipid (LP / LL) diet displayed lower final mean weight compared to fish fed the high protein (HP / LL and HP / HL) diets. The overall SGR was higher in the HP / LL group compared to both low protein groups and the MP / LL group. The calculated feed conversion efficiency (FCE) demonstrated that turbot are able to utilize high lipid feed efficiently and that lipids are essential when fish are fed diets with reduced amounts of protein. No clear relationship was found between CP content in feed and CP in fillet. CL in fillet were, however, affected by dietary CL, where fish fed the LP / HL and MP / HL diets had elevated levels of CL in fillet. The diets did not affect the texture properties of the fillet, whereas some differences were found regarding water holding capacity (WHC) and muscle pH in fillet. The present findings suggest that CP can be reduced by approximately 10% compared to current level in commercial feed without negative effects on growth. This will make production of a more cost efficient and less expensive feed for large turbot (> 500 g) possible.