A NOVEL PREBIOTIC IN AQUAFEEDS FOR Totoaba macdonaldi
The substitution of fishmeal (FM) in diets for carnivorous fish species is one of the foremost concerns in aquaculture and has prompted the search for new alternative protein sources. Poultry by-product meal (PBM) and defatted soybean meal (SBM) are considered a viable alternative to replace part of FM in marine fish diets due to their high availability, adequate-protein content and a low cost. However, the increase in SBM inclusion in fish diet is related to the occurrence of intestinal impairment in totoaba (Totoaba macdonaldi) Fuentes-Quesada et al., (2018). Prebiotics can be used as a nutritional strategy in an attempt to protect the intestine, reducing the occurrence of enteropathies. A new prebiotic obtained from a plant grown in Mexico has been investigated in animal nutrition and shown to confer benefits for the host health by providing specific changes in the structure and composition of the gut microbiota in mammals, but has not been evaluated in fish. Thus , the objectives of this study were to evaluate the effect of a new prebiotic in formulations for totoaba containing PBM and SBM on growth performance, gut integrity stress gene expression, microbiota, and economic and sustainability indexes.
F our isoproteic and isolipidic diets (51%CP and 12%CL) were formulated; one with FM as the main protein source and designated the reference diet (RD), a second diet with a blend of FM and PBM (FM-PBM; 1:2) and a third diet using the latter formulation together with 24% SBM (SBM-B) which has been shown to induce enteritis in fish. The fourth diet was exactly the same formulation as the third diet SBM-B, but supplemented with 2% prebiotic (P) (SBM-B+P ).
After feeding Totoaba macdonaldi juveniles (60.8 ± 22.6 g) for 44 days, the diet with the prebiotic, SBM-B+P , resulted in significantly higher growth compared to the other treatments. Moreover, 2% prebiotic supplement in the feed containing SBM improved the overall performance in totoaba. The use of this new prebiotic reduced the negative effects of SBM on intestinal health by maintaining the height of the brush border and reduce the expression of genes igm and il-β related with gut inflammation . Additionally, the presence of the prebiotic resulted in a reduction of the percentage of mucosal folds with wider submucosal epithelium increasing the somatic intestinal index. While, the prebiotic did not ameliorate the infiltration of eosinophilic granulocytes in the submucosal epithelium, its use has a great potential. However, more research is needed to elucidate the underlying mechanisms by which this improvement in growth and intestinal health is brought about. The supplementation of this prebiotic in diets reduced the FM protein dependency ratio resulting in better economic conversion ratio.
Lastly, the presence of this prebiotic in the diets significantly changed the bacteria present in the gut by enriching the Anaerolinaceae family, characterized by nitrogen fixation, suggesting that this change in the microbiota could participate in nitrogen fixation improving the protein efficiency ratio.
Fuentes-Quesada, J.P., et al., 2018. Aquaculture, 495: 78-89