Replacement of fish meal with wheat gluten in diets for Atlantic halibut ( Hippoglossus hippoglossus): Effect on whole-body amino acid concentrations

Abstract

The feasibility of replacing fish meal with wheat gluten (WG) in diets for Atlantic halibut ( Hippoglossus hippoglossus) was studied. Four diets were produced containing 0, 10, 20 and 30% WG (60% crude protein and 27% lipid (dry matter (DM) basis)). The lysine concentration in these diets were 4.0, 3.6, 3.1 and 2.6% (dehydrated form), respectively. The diets were fed to triplicate groups of 60 g halibut in a 56-day comparative slaughter experiment. The data were analysed by ANOVA and regression. Fish growth (specific growth rate, overall mean 1.25 ± 0.03%/d) and feed efficiency (overall mean 1.63 ± 0.03 g gain/g DM intake) were good in this trial and were not influenced by dietary WG level. The whole-body protein concentration decreased significantly and the crude lipid concentration tended to increase with increasing dietary WG. These observations were taken as indications of problems with amino acid metabolism, and it was assumed that the diet containing 2.6% lysine was deficient in this amino acid. It was observed that the method of expression of the amino acid concentrations in the body was crucial for the detection of significant differences among treatments. Based on our results, we caution the use of crude protein as the denominator in the expression of amino acid concentrations. The finding in this dataset that dietary effects on the percentages of some amino acids in the fish are dependant on the use of hydrated or dehydrated amino acids encourages us to express the amino acids in the protein-bound (dehydrated) form, which also represents the form in which the overwhelming majority of amino acids are present in the body. The results from this trial indicate that WG is a suitable replacement protein source for fish meal, even at a high inclusion level of 20% of the diets. A further increase in the dietary WG level to 30% should be done with caution unless the diets are supplemented with lysine.