Supplementation of Rhodotorula paludigena CM33 in Feed as Probiotic Enhances Growth, Immunity, Gene Expression, and Disease Resistance to Aeromonas hydrophila in Red tilapia (Oreochromis niloticus × O. mossambicus)

Dietary supplementation with red yeast (RY) has been proposed to enhance immunity and disease resistance in fish; however, its effects in red tilapia remain underexplored. This study evaluated the impact of Rhodotorula paludigena CM33 on growth performance, immune responses, liver and intestinal histology, gene expression, and resistance to Aeromonas hydrophila in red tilapia. A total of 300 fish were assigned to five dietary groups: RY-0 (control), RY-5 (5 g/kg), RY-10 (10 g/kg), RY-20 (20 g/kg), and RY-40 (40 g/kg). Growth performance was assessed at weeks 4 and 8. At week 8, blood serum, liver, and intestinal samples were collected for histological and gene expression analyses. Fish were then challenged with A. hydrophila at an LD₅₀ dose of 10⁵ CFU/fish via intraperitoneal injection. Results showed that R. paludigena CM33 significantly improved growth performance, with polynomial regression identifying ~ 24 g/kg as optimal, and experimental fish fed 20 g/kg achieved the highest weight, gain, and feed efficiency. Antioxidant and immune responses were enhanced, as evidenced by increased ABTS radical scavenging activity, superoxide dismutase activity, and upregulation of immune-related and antioxidant genes ( IL1, MHC, LBP, GSR, GPX, IGF, HSP70 , and TNF ). Histological analysis revealed enhanced intestinal structure and hepatocyte integrity, with RY-20 fish exhibiting elongated villi and reduced hepatic vacuolation compared to the control. Kaplan-Meier survival analysis confirmed greater resistance to A. hydrophila at the 20 g/kg inclusion level. These findings highlight R. paludigena CM33 as a promising dietary supplement for enhancing growth, immune function, and disease resistance in red tilapia.