Gluten-free Fish? Marine Carnivores Cobia (Rachycentron canadum) and European Sea Bass (Dicentrarchus labrax) Have Different Tolerances to Dietary Wheat Gluten

In developing more sustainable fishmeal-free diets for a broad range of fish species, a \"one-size-fits-all\" approach should not be presumed. The production of more ecologically sustainable aquaculture diets has increased the incorporation of plant-based protein sources such as wheat gluten. Here we show that wheat gluten at even less than 4% inclusion in a compound feed has a negative impact on growth and survivorship in juvenile cobia (Rachycentron canadum). In addition, plasma factors capable of binding wheat gluten were detected in the plasma of cobia fed diets containing this ingredient but not in wild cobia with no exposure to dietary wheat gluten. Furthermore, there is evidence that supplementary taurine partially mitigates the deleterious effects provoked by wheat gluten. Based on these results, we propose that wheat gluten should be added with caution to aquaculture diets intended for juvenile cobia and potentially other marine carnivores. After observing that dietary wheat gluten can cause deleterious effects in cobia, we sought to evaluate a possible effect in European sea bass (Dicentrarchus labrax), another large, carnivorous, marine species. There were no major effects in terms of growth rate, plasma biochemical parameters, or detectable induction of plasma IgM, IgT, or factors capable of binding gliadin in response to 4% dietary wheat gluten. However, plasma levels of taurine doubled and there were considerable changes to the intestinal microbiome. There was increased diversity of predominant taxonomic orders in the pyloric caeca, anterior, middle, and posterior intestinal sections of fish consuming wheat gluten. Despite these measurable changes, the data suggest that dietary inclusion of 4% wheat gluten is well tolerated by European sea bass in feed formulations. Together these findings underscore the need to evaluate tolerance to ingredients in aquaculture formulations on a species by species basis.