Antioxidants and immune responses, resistance to Aspergilus flavus infection, and growth performance of Nile tilapia, Oreochromis niloticus, fed diets supplemented with yeast, Saccharomyces serevisiae
2020
Abdel-Tawwab, Mohsen | Adeshina, Ibrahim | Issa, Zeenat A.
Yeast, Saccharomyces cerevisiae, is a single cell fungus, which contains various immune-stimulant compounds such as β-glucans, nucleic acids, oligosaccharides and chitin among others. So, it has been used as a probiotic in aqua-feeds. A feeding trial was conducted to examine the effects of dietary yeast supplementation on growth, hematological, antioxidant, and immune biomarkers of Nile tilapia, Oreochromis niloticus as well as its resistance to pathogenic fungus Aspergilus flavus infection. Five isonitrogenous diets containing 0 (control), 2, 4, 6, and 10 g yeast/kg diet were formulated and fed to triplicate groups of fish (2.4 ± 0.14 g) for 8 weeks. After that, fish were intraperitoneally injected with pathogenic fungus, A. flavus and observed for any clinical signs and mortality for 14 days. It is noticed that dietary yeast levels linearly and quadratically enhanced (P < 0.001) the growth performance of Nile tilapia and the feed intake but not feed conversion ratio. Also, dietary yeast administration to fish significantly improved (P > 0.05) their intestinal villi length/width and absorption area. Linearly and quadrically increases were observed in counts of red blood cells, white blood cells, and platelets as well as hemoglobin and hematocrit values accompanied with linear and quadric decreases in heterocytes and monocytes percentages due to dietary yeast administration to Nile tilapia. Further linear and quadric (P < 0.001) enhancements of superoxide dismutase, catalase, and glutathione peroxidase activities as well as activities of respiratory burst and lysozyme accompanied with linear and quadric reduction (P < 0.001) in the malondialdehyde level along the yeast supplementation levels. After A. flavus challenge, highest mortality (36.7 %) was observed in fish fed the control diet, while no mortality was obtained in fish fed 6–10 g yeast/kg diet. The present study showed that dietary yeast, S. serevisiae, strongly improved growth, hematological, antioxidant, and immune responses of Nile tilapia and its resistance against pathogenic fungus A. flavus infection with an optimum inclusion level of 6 g/kg diet.
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