Dietary mannan-oligosaccharides enhance hematological and biochemical parameters, reproductive physiology, and gene expression of hybrid red tilapia (Oreochromis niloticus x O. mossambicus)

This study was carried out to evaluate the effects of dietary supplementation of mannan-oligosaccharides (MOS) on physiological performance, reproduction capacity and gene expression of hybrid red tilapia (Oreochromis. niloticus x O. mossambicus) broodstock reared in concrete tanks (3.5 × 3.2 × 0.9 m). Four isonitrogenous (30% cp), isocaloric (18.72 MJ kg−1) diets containing 0.0, 0.5, 1.0 and 1.5 g kg−1 MOS were prepared. The diets were fed to triplicate groups of red tilapias broodfish (155 ± 5.65 g) stocked at a male: female ratio of 1:3, to satiation twice a day for two months. At the termination of the feeding trial, fish in each tank were netted and weighed. Blood samples were collected from five fish per tank to determine the hematological and biochemical parameters. The fish were then dissected for assessing the reproductive performance and its related genes. The results indicate that the values of hematological parameters (RBCs, Hb, and Htc) total protein, albumin, globulin, and reproductive hormones (testosterone, follicle-stimulating hormone and luteinizing hormone) were significantly increased by MOS dietary inclusion (1.0–1.5 g kg-1), while liver function enzymes including alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were significantly decreased in fish fed with 1.5 g /kg of MOS (p < 0.05). Reproductive performances, including GSI, total number of fries per female and mean fry weight were significantly improved with increasing dietary MOS to 1.5 g kg−1. Gonads maturation was also enhanced with supplemental MOS to 1.5 g kg−1. In males, the highest testosterone concentration was recorded at 1.5 g MOS kg−1 diet. In females, FSH and LH were significantly increased with increasing MOS levels up to 1.0 g kg−1, and then leveled off. Conversely, the highest E2 and Prog concentration was obtained at 1.5 g kg−1. The expression of CYP19a, FSHR, FOXL2, CYP1A, ESR1, and ESR2A were significantly upregulated in the gonads of fish fed diets treated with MOS, up to a concentration of 1.5 g kg-1. These results suggest that a dietary supplementation of MOS (1.5 g kg−1) could enhance the reproductive performance of red tilapia.