Metabolizable energy from dietary carbohydrates in turbot, Scophthalmus maximus (L.)

Abstract

Abstract. In a feeding experiment, the metabolizability of dietary carbohydrates in diets for turbot, Scophthalmus maximus (L.), was estimated and expressed as percentage of the metabolizability of dietary lipids. Four isoenergetic and isonitrogenous dietary treatments were applied with varying percentages of non-protein energy presented as starch. In order to obtain results allowing quantitative interpretation, an experimental design was used in which effects are reflected in varying body fat depositions only. Two methods were used simultaneously to overcome practical problems associated with differences in energy density between carbohydrates and lipids. The conventional method was based on equal feeding rates combined with the inclusion of inert filler in the diets, whereas the alternative method applied different dietary nutrient percentages in combination with different feeding rates. Although similar results were obtained, the alternative method was more convenient to use than the conventional method. Because of the experimental strategy applied, no significant effects on growth and protein utilization were obtained, but lipid deposition rates were significantly reduced at increased percentages of non-protein energy presented as starch. The metabolizable fraction of the gross dietary carbohydrate energy was estimated as 67% of that of dietary lipids. This reduction does not indicate that turbot have any systematic deficiency in metabolizing dietary carbohydrates.