EVALUATION OF A SOLUBLE MANNAN RICH FRACTION IN THE FERTILIZATION OF RAINBOW TROUT Oncorhynchus mykiss EGGS

The mannan oligosaccharide (MOS) component of the yeast cell wall has been shown to improve fish performance when applied through the feed. Increasing challenges in the aquaculture industry provide an opportunity to evaluate novel applications of MOS compounds to improve performance while reducing the impact of disease.  A water-soluble fraction of MOS (MRF) has been developed to improve the health of fish through a modulation of the innate immune response. Multiple studies were performed to evaluate the impact of MRF when applied during the fertilization of Rainbow trout eggs. The initial study evaluated the eyed egg percentage and hatching percentage followed by an 8-week feeding trial. A total of 300 Rainbow trout eggs in 100 ml of D532 (5.52 % NaCl; 3.74 % Glycine; 2.42 % Tris; pH 8.8) were exposed to two levels of MRF (0.10 mg/ml and 0.50 mg/ml) with a no exposure control during fertilization. The exposure of eggs to MRF during fertilization increased the percent of eyed eggs from 90 percent (no exposure) to 95 percent for the 0.10 mg treatment and 94 percent for the 0.50 mg treatment. The percent hatch increased from 83 percent (no exposure) to 93 percent for the 0.50 mg treatment and 86 percent for the 0.10 mg treatment group . Average weight gain was numerically increased following exposure to MRF but the differences were not significant (Table 1). In a second study, following exposure and maturation to the eyed egg state the changes in gene expression patterns were determined using a salmonid gene chip (Affymetrix). The design consisted of one MRF level (50 mg) and a control with no MRF exposure.  Exposure of MRF to Rainbow trout eggs altered the expression of 430 transcripts in the eyed eggs. The exposure of Rainbow trout eggs to MRF resulted in the change in expression patterns of genes that are important in embryo development, represented by increased expression of genes important in calcium metabolism and bone development, eye lens development and muscle cell growth.  Exposure of Rainbow trout eggs to MRF during fertilization changed the expression pattern of eggs as soon as 21 days after exposure as well as 8 weeks after hatching,