Over the past two decades, aquafeeds have progressed towards the inclusion of non-traditional protein sources that are lower-cost, sustainable alternatives to fully or partially replace fishmeal in fish feed. Alternative protein sources include those derived from soy (i.e.: plant), where soybean meal (SBM) represents a high-protein and low-cost source. However, high inclusion levels of SBM in salmonids cause detrimental effects including intestinal dysfunction and soybean meal-induced enteritis (SBMIE), mainly attributed to anti-nutritional factors (ANFs). Despite these results, the mechanistic effects of ANFs on nutrient absorption remain unclear. Therefore, if we can understand how ANFs affect the intestinal nutrient transport mechanisms, we can work to isolate and eliminate specific ANF components, thus working towards mitigation solutions to incorporate higher inclusion levels of soy.
Here, we report the baseline characterization of methionine transport along the mid-intestine of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), and the effects of select isolated ANFs (i.e.: lectin, soya saponin, and β-conglycinin) on methionine absorption. Since SBM is limiting in methionine, an essential amino acid critical for protein synthesis and fish growth, it is crucial to investigate methionine absorption and its potential impedance by ANFs in both species. Specifically, electrogenic and total methionine flux were measured on Ussing chambers using ex vivo mid-intestinal segments. Additionally, baseline transepithelial electrical resistance (TEER) and conductance, including changes to TEER in response to the different ANFs, were evaluated to measure intestinal barrier function. For ANF characterization, specific doses were added after each mid-intestinal segment reached a final methionine concentration of 20mM. This ensured methionine transporters were at their maximal rate. In Atlantic salmon, a sequential dose response for the ANF lectin (0.01µM, 0.1µM, and 1µM) revealed no significant differences in TEER from the 20mM point (Figure 1). This can possibly suggest that the addition of lectin isolate to the Ussing chamber may not elicit a strong effect. However, different results may arise from our methionine flux and the other ANFs being assessed. The continuation of this study includes evaluating changes in methionine absorption and gut barrier function in both species in response to feeding SBM- versus fishmeal-based diets.