Dietary Hydrolyzed Yeast Improves Growth, Gut Health, and Selective Gene Expression of Nile Tilapia (Oreochromis niloticus)

The effects of graded levels of hydrolyzed yeast (HY) supplementation (0.0, 0.5, 1.0, and 2.0 g/kg, i.e., Control, HY0.5, HY1.0, HY2.0, respectively) on growth performance, gut health, and immune responses of juvenile Nile tilapia (Oreochromis niloticus) were assessed in this study. The experiment was conducted in a completely randomized design for 14 weeks, where the treatments were distributed in 16 300-L tanks with four replicates each. Despite no significant differences, the final body weight and weight gain were numerically higher in treatments containing HY (44.7 and 34.7 g, 43.5 and 33.5 g, and 45.5 and 35.5 g in HY0.5, HY1.0, and HY2.0, respectively). Feed efficiency (FE) was improved linearly (p < 0.05) with increasing dietary HY level (0.65, 0.70, and 0.72, respectively). Similarly, there was also a significant linear relationship between protein deposition (PD), as well as protein and energy retention efficiency (ERE), with the increasing dietary HY level. Among the blood parameters, only the hematocrit (HCT) value was significantly lower in HY1.0 and HY2.0 compared to the control and HY0.5 treatments. Gut histology showed significantly higher villi length in fish fed HY2.0 diets (795 ± 89.6 µm) compared to those fed the control diet (504 ± 80.7 µm). The average surface volume (SV) of the villi was also higher in tilapia fed HY0.5, HY1.0, and HY2.0 diets (0.025, 0.026, and 0.038 mm³, respectively) compared to the control diet (0.021 mm³). All four target genes were significantly upregulated in HY1.0 and HY2.0 treatments. The expression of the genes supporting growth and ATP production, insulin-like growth factor-1 (IGF-1) and glyceraldehyde-3-phosphate (G-3-P), respectively, was significantly improved, as well as the expression of the immune-related gene, hepcidin. The expression of ghrelin also showed a significant increase with increasing HY levels. It can be concluded that the HY supplementation improved feed utilization, gut health, nutrient absorption capacity, and immunity in Nile tilapia.