EFFECTS OF VARYING LEVELS OF BREWER’S GRAINS AND AMINO ACID SUPPLEMENTATION ON GROWTH PERFORMANCE OF JUVENILLE NILE TILAPIA Oreochromis niloticus

Tilapia are currently the second most popular farmed fish globally behind only carp. The success of tilapia as a farmed food-fish is based partly on their ability to efficiently utilize plant products as feed lending to both economical and sustainable production. The incorporation of locally available by-products has the potential to reduce feed and production costs. Currently, there are over 4,000 breweries in the United States. Brewer's grains (BG) are the solid residue left after the processing of cereal grains for the production of beer. BG are a concentrate of protein and fiber remaining after most of the sugar has been extracted from the mash. Tilapia have been shown to be unique in their ability to digest fibrous plant materials and are often fed agricultural and industrial by-products in other parts of the world.

An eight-week feeding trial was conducted to evaluate the effects of adding increasing levels of BG into diets fed to Nile tilapia (Oreochromis niloticus). Ten juvenile tilapia (average weight 6.6 g) were stocked into each of sixteen 38 L aquaria with four aquaria per dietary treatment. Fish were fed three times daily one of four experimental diets containing either 0% BG (Control), 15% BG, 30% BG or 30% BG with added crystalline amino acids (AA; 30% BGwAA). In the 30% BGwAA treatment 0.35% Methionine and 0.35% Lysine were added to the formulation. The Control diet was modeled after a traditional commercial tilapia diet.  All diets contained 8% fish meal and were formulated to be isocaloric and isonitrogenous. Added BG replaced conventional soy bean meal and wheat flour in the formulations.

Water quality variables remained acceptable for tilapia production throughout the trial. After eight weeks, there was no significant difference (P>0.05) in survival among treatments (Table 1). The average weight (g) and specific growth rate of fish fed the Control and the 15% BG were statistically similar although they were both greater (P<0.05) than those for fish fed diets 30% BG (Table 1). Feed conversion ratio (FCR) was more efficient for fish fed the Control diet than for fish fed both 30% BG and 30% BGwAA.  FCR for fish fed the 15% BG was better than for fish fed 30% BGwAA but was not different from the other diets (Table 1). Consumption was reduced in fish fed diets containing BG compared to the Control diet (Table 1). Based on these data, juvenile tilapia fed diets containing 15% BG resulted in acceptable growth and FCR while fish fed diets containing 30% BG resulted in a growth reduction and increased FCR.