Effects of Yeast Oligosaccharide Diet Supplements on Growth and Disease Resistance in Juvenile Nile Tilapia, Oreochromis niloticus

Authors: Shelby, Richard; Lim, Chhorn; Aksoy, Mediha; Welker, Thomas; Klesius, Phillip

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2008
Publication Date: 2/1/2009
Citation: Shelby, R.A., Lim, C.E., Aksoy, M., Welker, T.L., Klesius, P.H. 2009. Effects of yeast oligosaccharide diet supplements on growth and disease resistance in juvenile Nile tilapia, Oreochromis niloticus. Journal of Applied Aquaculture. 21:61-71.

Interpretive Summary: Yeast subcomponents, consisting mainly of oligosaccharides or beta-glucans, have been shown by other researchers to have beneficial effects when included as dietary supplements in fish diets. They have been mostly considered to be both humoral and cellular immunostimulants, but other beneficial effects have included enhanced survival, disease resistance, and reduced spinal malformations. We used commercially available yeast and yeast oligosaccharide preparations as supplements in prepared feed to test the efficacy of these preparations in juvenile Nile tilapia. We added these ingredients to ground commercial feed at the varying rates (0.1-10.0 g/kg) and re-pelletized the treated feeds. These diets were fed twice daily to apparent satiation for periods of 2 and 4 weeks. We recorded weight gain, feed efficiency, serum protein, immunoglobulin, lysozyme, and complement levels. Following the feeding period tilapia were disease-challenged with pathogenic bacteria Streptococcus iniae or Edwardsiella tarda. Mortality, morbidity, and specific antibody response were recorded. We conducted 3 separate experiments involving over 1000 fish at 3 different stocking densities. Significant differences were observed in weight gain, feed intake, and moribund fish following disease challenge, however, in no case did the addition of yeast components improve the overall yield or disease resistance compared to fish receiving the control diet. We conclude these commercial yeast subcomponent preparations do not enhance weight gain or disease resistance in juvenile Nile tilapia when fed at these rates and under these particular conditions.

Technical Abstract: Commercially available yeast, and yeast subcomponents consisting mainly of beta-glucan or oligosaccharide feed additives, were added to diets of juvenile (12-18g) Nile tilapia (Oreochromis niloticus) at rates recommended by suppliers. Three experiments followed a basic protocol with varied rates of supplementation, duration of feeding, and stocking densities. Experimental diets were fed twice daily to apparent satiation for a period of 2 or 4 weeks, at the end of which feed consumption and weight gain were measured. Following the experimental feeding period, serum components including protein and immunoglobulin concentrations, as well as lysozyme and complement activities were measured. A disease challenge was conducted with pathogenic isolates of Streptococcus iniae or Edwardsiella tarda. Weight gains were not significantly different in fish fed the supplemented diets when compared to the control diet. Differences in feed consumption were not consistent between experiments, and overall feed efficiency was not significantly affected by diet. There were no differences in serum components of fish samples at 2 or 4 weeks. Fish fed the experimental diets did not have lower mortality or morbidity after disease challenge compared to fish fed the control diets. Specific antibody against S. iniae or E. tarda measured by ELISA, did not reveal differences in antibody responses in the fish surviving the challenge injections. We conclude that the incorporation of these commercial yeast component products into the diet of juvenile Nile tilapia at these rates and for these feeding periods had no effect on growth, serum components, antibody responses or survival following S. iniae or E. tarda infection.