Utilization of baker’s yeast waste fermented rice bran as a nutritive feed component for silver carp (Hypophthalmichthys molitrix)

Fermenting rice bran with baker’s yeast waste introduces a cost-effective, eco-friendly method of valorizing these waste streams into high-value fish feed. This practice not only reduces environmental pollution but also addresses the challenge of sustainable aquaculture inputs. A study was designed to evaluate the impact of baker’s yeast waste (BYW)-fermented rice bran (FRB) on the growth performance, feed efficiency, impact on digestive and antioxidant enzymes, whole-body proximate composition, and hematological indices of silver carp (Hypophthalmichthys molitrix) fingerlings. Rice bran was fermented with BYW for 20 days and then used in the fish feed at incremental inclusions. Five diets were formulated, including the control diet (0%), 5%, 10%, 15%, and 20% FRB. The acclimatized fingerlings (N = 300; average initial weight, 5.65 ± 0.01 g) were distributed into five treatment groups (20 fish/triplicate) and fed at 3% body weight two times a day for 90 days. At the time of harvesting, the growth performance, feed efficiency, crude protein, crude ash, red blood cells, and hemoglobin of H. molitrix were significantly greater in the FRB20 group (20% FRB) than in the UFRB group (0% FRB), i.e., the control group, while no significant differences (p > 0.05) were detected in white blood cells, hematocrit, or mean corpuscular hemoglobin among all treatments. Serum biochemical analysis revealed that the globulin and total protein levels were significantly elevated in the FRB20 group. The levels of digestive enzymes (protease and amylase) and antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase) were increased significantly in the FRB20 group (p < 0.05), and the lowest level of malondialdehyde was detected in the FRB10 group, while the level of lipase (p > 0.05) did not significantly differ among the treatments. These findings indicate that the inclusion of 20% fermented rice bran enhanced the growth performance and overall performance of fish. Therefore, the addition of 20% fermented rice bran (FRB) to the diet can effectively improve the health of H. molitrix fingerlings. However, further research should be conducted to investigate the long-term effects of FRB on fish growth, health, and evaluate its economic feasibility as its utilization in long term might have negative effects.