Preliminary Assessment on the Effects of Dietary Protein Changes and Methionine Supplementation on the Gene Expression of Amino Acid Transporters slc6a19 and slc15a1a in the Intestine of Nile Tilapia

This study investigates the impacts of dietary changes on amino acid transporters – slc6a19 and slc15a1a – in the intestine of Nile tilapia. Adult Nile tilapia (average weight = 130 ± 9.8 g) were subjected to sequential feeding using isonitrogenous (30%) and iso-lipidic (5%) diets, which consisted of fishmeal, soybean meal (SBM), and SBM with 4 g kg–1 methionine as the main source of dietary protein. Fish were first fed a fishmeal-based diet for 1 wk, which was changed to a SBM-based diet on the second and third week and finally to a SBM with 4 g kg–1 methionine on the fourth and fifth weeks. Intestinal tissue samples were collected every week. To determine the spatial response of slc6a19 and slc15a1a in the intestinal length of tilapia, the intestine was divided into five segments – namely hepatic loop, proximal major coil, gastric loop, distal major coil, and terminal segment. The results indicated that the hepatic loop exhibited a decrease in slc6a19 expression, following the shift from fishmeal to SBM diet. However, this expression was gradually increased when the diet was switched to SBM with methionine. A comparable pattern was observed in the proximal major coil for slc15a1a expression upon transitioning from fishmeal to SBM with a methionine diet. The study found that these genes in tilapia responded to dietary changes, potentially serving as molecular biomarkers for nutritional status. This sheds light on amino acid and oligopeptide absorption mechanisms in the intestinal epithelium of Nile tilapia, improving our understanding of fish nutrition and feed formulation.