ABSTRACT
This study was conducted to evaluate the effect of dietary levels of Brewtech dried brewers yeast (BY) and GroBiotic-A (GB) on growth performance, proximate body composition, immune response, and resistance of juvenile Nile tilapia to Streptococcus iniae challenge. A practical basal (control) diet formulated to contain approximately 32% crude protein and 6% lipid was supplemented with 1% and 2% of BY or GB. Each diet was fed to Nile tilapia in quadruplicate aquaria for 12 weeks. Weight gain, feed intake, survival, and whole body proximate composition of 198 fish were not significantly affected by dietary treatments. Serum total protein, total immunoglobulin, lysozyme, and agglutinating antibody titer to S. iniae were not significantly affected by dietary supplementation of BY or GB. However, serum haemolytic complement activity (SH50) of fish fed 1% BY was significantly higher than those of fish fed the control diet and diets supplemented with 2% BY or GB. Cumulative mortality of fish 20 days post-challenge with S. iniae was unaffected by dietary treatments. However, fish fed diets supplemented with 1% BY and 2% BY or GB had substantially reduced and earlier cessation of mortality.
The authors would like to thank Suranaree University of Technology, Rajamangala University of Technology Isan, and the Aquatic Animal Health Research Unit, USDA-ARS, MSA, for funding support of this project; International Ingredient Corporation (St. Louis, MO, USA) for donation of GroBiotic-A and Brewtech dried brewers yeast; and Ms. Rashida Eljack, Aquatic Animal Health Research Unit, USDA ARS, Auburn, Alabama, for technical assistance.
