Use of non-starch polysaccharides by juveniles of Mugil liza mullet (Valenciennes, 1836)
With the growing expansion of aquaculture worldwide, it is necessary to reduce dependence on fishmeal combined with the study of sustainable and environmentally friendly alternative foods. However, the presence of antinutritional factors and fibrous components in these plant products means that their use in the feeding of aquatic organisms is limited, mainly due to the lack of knowledge of the actions of these foods on the target organism. The objectives of the present study were to evaluate the effect of guar gum (GG - experiment 1) and citrus pectin (PC - experiment 2), two soluble non-starch polysaccharides (PNAs), on growth, proximal composition, intestinal tract morphology , microbial community and liver parameters of juveniles of Mugil liza mullet. Still, to evaluate the inclusion of exogenous enzymes (experiment 3) in a soybean meal based ration and to verify performance, muscle proximal composition, intestinal histology, microbial tract community and deposition of Ca and P in the bones. For the first and second experiment, a purified basal diet was formulated without significant levels of fiber and three levels of non-starch polysaccharides (4, 8 and 12%), guar gum (experiment 1) and citrus pectin (experiment) 2) over 60 days. The results of experiment 1 indicate that guar gum acted as an anti-nutritional factor with the inclusion of 8 and 12%, reducing the animals' performance. The addition of GG altered body composition, glycogen and hepatic cholesterol in addition to the microbial community in different sections of the tract,however, no changes were observed in the tract morphology. In experiment 2, the inclusion of different CP levels did not change performance, but it did change body composition and hepatic glycogen. There was no modulatory effect in the microbial community and the fish fed with PC showed intestinal lesions similar to enteritis. In experiment 3, a basal diet composed of soybean meal as the main protein source (control) was supplemented with four levels of exogenous enzyme cocktail (50, 100, 150 and 200 g t-1) and supplied to the fish for 75 days. There was no improvement in performance, changes in muscle composition and microbial community. Greater Ca retention was found in the bones of fish fed with the inclusion of enzyme. Fish fed with the control diet showed mild to severe morphological changes, with necrosis and changes in the intestinal villi, which in the long run, can compromise performance. Animals fed with enzyme supplementation in the diets did not develop any intestinal pathology, indicating that the exogenous enzymes may have eliminated or neutralized the anti-nutritional factors present in the soybean meal. As a conclusion, it is recommended to use GG as a binder in mullet diets only up to the level of 4%; the use of PC in diets as binders for this species must be cautious when performed for long periods; and the addition of exogenous enzymes has the potential to mitigate intestinal injuries induced by the inclusion of soybean meal in Mugil liza diets.