Fish have been shown to present an opposite trend to mammals with an increase in feed intake of diets that are imbalanced in essential amino acids (EAA). However, fish response to individual dietary EAA deficiencies remains unclear. The objective of this study was to assess the effect of EAA deficiency on feed intake, growth performance, muscle post-prandial free amino acid (FAA) levels, and the expression of genes associated with amino acid sensing in the intestinal tract using Zebrafish Danio rerio as a model species.
Six semi-purified diets were formulated for this study. The first diet, CG, contained casein and gelatin as its only protein sources. The remaining five diets had 50% of its protein supplied through casein and gelatin, and the other 50% supplied in the form of free amino acids (FAA50). The FAA50 diet was formulated to contain the same level of amino acids as the CG diet. The (-) Lys, (-) Met, and (-) Thr diets were formulated to match the FAA50 diet, but were deficient in lysine, methionine, or threonine, respectively. Finally, the Deficient diet was not supplemented with any of the three EAA. At 21 days-post-hatch, Zebrafish were randomly distributed in 18 (3 L) tanks, with 30 fish per tank in three replicates per dietary treatment. The fish were fed three times a day to satiation, and the study lasted until 50 days-post-hatch.
At the conclusion of the study, the feed intake of the CG group was significantly higher than all other groups. Neither the (-) Lys, (-) Met, or (-) Thr groups had a feed intake that was significantly different from that of the FAA50 group. However, the feed intake of the Deficient group was significantly higher than the feed intake of the FAA50 group. The feed efficiency (FE) of the (-) Lys and Deficient groups was significantly lower compared to the CG group. The FE of the FAA50, (-) Met, and (-) Thr groups were not significantly different from any of the other groups. The final weight and weight gain (%) of the CG group was significantly higher than all other groups and there were no significant differences in growth between the FAA50 group and any of the groups with EAA deficiencies. Additionally, survival did not significantly vary between any of the groups. Overall, the results from this study show that Zebrafish do not significantly adjust their feed intake in response to individual deficiencies of lysine, methionine, or threonine, but the apparent additive effect of a combined deficiency of the three EAA triggered a significant increase in feed intake as a response. The results on muscle post-prandial FAA levels and gene expression will be included in the oral presentation.