Addition of ß-glucans in diets for tropical gar (Atractosteus tropicus) larvae: effects on growth, digestive enzymes and gene expression of intestinal epithelial integrity and immune system.

The effect of ß-glucans 1,3/1,6 from Saccharomyces cerevisiae yeast at different inclusion percentages (0.0, 0.2, 0.4, 0.6, and 0.8%) in the diet for tropical gar (Atractosteus tropicus) larvae was evaluated on growth, digestive enzyme activity and, relative expression of the immune system genes. The bioassay started on the third day after hatching (DAH) and lasted 21 days, using a total of 1500 larvae of 0.055 ± 0.008 g and, a total length of 2.46 ± 0.26 cm. Larviculture was carried out in a recirculation system with 15 tanks of 70 L using a density of 100 organisms per experimental unit. No significant differences in larval growth were observed by the inclusion of ß-glucans (p > 0.05). Digestive enzymes showed changes in lipase and trypsin activities, presenting higher values in fish fed 0.6% and 0.8% ß-glucans diets compared to the other treatments (p < 0.05). Leucine-aminopeptidase, chymotrypsin, acid phosphatase, and alkaline phosphatase activity showed higher activities in larvae fed with a 0.4% ß-glucan diet compared to the control group. The relative expression of intestinal membrane integrity (mucin 2) muc-2, (occludins) occ, (nucleotide-binding oligomerization domain) nod-2, and immune system lys (lysosome) genes showed over-expression in larvae fed the 0.4% ß-glucan diet to the rest of the treatments (p < 0.05). The inclusion of ß-glucans at 0.4-0.6% in diets for A. tropicus larvae could improve larviculture, as effects on the increase in the activity of several digestive enzymes and the expression of genes of the immune system.

Protein and lipid requirements of three-spot cichlid Cichlasoma trimaculatum larvae.

Determination of the main nutritional requirements at different developmental stages is a prerequisite in the formulation of feeds for newly cultured fish species. In the present study, the lipid and protein requirements of larvae of a native Mexican fish, the three-spot cichlid Cichlasoma trimaculatum, were assessed using a two-factor experimental design that considered four protein (35, 40, 45, and 50%) and two lipid levels (16 and 22%) on growth, survival, and digestive enzyme activities. The best growth and feed efficiency results were obtained when larvae were fed diets including 45% protein and 22% lipids. Comprehensive evaluation of the profile of digestive enzymes using multivariate analysis also demonstrated significant differences in nutritional condition generated by varying inclusion of nutrients. Thus, an increase in protein led to an increase in alkaline protease activity and a reduction in leucine aminopeptidase activity, and the reduction of dietary lipid content led to a significant increase in lipase and trypsin enzymatic activities. Based on our results, C. trimaculatum larvae have a high capacity to hydrolyze both nutrients (protein and lipids) for the high digestive enzyme activities and increase their growth, particularly with a diet containing 45% protein and 22% lipids.