The Use of Dipeptide Supplementation as a Means of Mitigating the Negative Effects of Dietary Soybean Meal on Zebrafish Danio rerio

Soybean meal (SBM) is the most common source of protein used to replace fishmeal (FM) in aquaculture diets. SBM inclusion in diets has been found to negatively affect growth and induce intestinal inflammation in fish. The objective of this study was to determine the effect of health-promoting dipeptide (carnosine, anserine, alanyl-glutamine) supplementation into SBM-based feeds on growth performance, intestinal health, and muscle free amino acid composition, an indicator of dietary amino acid availability, in a zebrafish model. There were 5 treatment groups in this study. The first group ( (+) Control ) received a FM-based diet. The second group ( (-) Control ) received SBM-based diet. The last three groups ( Ala-Glu, Car, and Ans) were fed SBM-based diets, supplemented with alanyl-glutamine, carnosine, and anserine respectively. All groups received their respective diets during 33-59 dph. The Ala-Glu and Car groups experienced a significantly higher weight gain than the (-) Control group, weighing 35.38% and 33.96% more, respectively at the conclusion of the study. There were no significant differences among gene expression between the groups, but Ala-Glu had the highest expression of both nutrient absorption genes measured, PepT1 and fabp2 . Ala-Glu had significantly longer intestinal villi, and a significantly higher villus length-to-width ratio than the (-) Control group. Among the free amino acid composition, the Car group had a significantly higher post-prandial concentration of lysine, compared to the (-) Control group. The increase in villi surface area and expression of nutrient absorption genes represent an improvement in intestinal absorptive capacity in the Ala-Glu group. The increase in lysine concentration may signify an increase in the retention of protein in the fish in the Car group. The results from this study provide support for the use of alanyl-glutamine and carnosine supplementation as a means of improving growth performance of zebrafish fed with a 100% SBM-based diet.