EVALUATION OF BREWERS GRAINS IN TILAPIA Oreochromis niloticus DIETS AS APPLIED TO INCREASING AQUAPONICS SUSTAINABILITY

Tilapia are a popular farmed food-fish worldwide and currently the most commonly used species in aquaponic production in the US. Tilapia are able to efficiently utilize plant products as feed, lending to both economical and sustainable production. However, the US imports most of the farmed tilapia available to consumers. One key factor is that feed costs for production are greater than 50% in the US. The incorporation of locally available by-products might reduce feed costs, with one potential source being the spent cereal solids left from brewing alcohol. These solids, called Brewer's Grains (BG), are a concentrate of protein and fiber remaining after most of the sugar has been extracted from the mash. Tilapia are unique in their ability to digest fibrous plant materials and are often fed agricultural and industrial by-products in other parts of the world. As breweries continue to thrive in the US, and considering the many small-scale breweries associated with craft beer, there could be locally-sourced material available at a very low cost for inclusion in to tilapia diets.

An eight-week feed trial evaluated the effects of adding increasing levels of BG into diets for Nile tilapia (Oreochromis niloticus). Ten juveniles (avg. weight 6.6 g) were stocked into each of sixteen 38-L aquaria with four replicates per dietary treatment. Fish were fed three times daily, one of four experimental diets containing either 0% BG, 15% BG, 30% BG or 30% BG with added crystalline amino acids (AA; 30% BGwAA) at 0.35% methionine and 0.35% lysine supplementation. The 0% BG was a control and modeled after a 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.

After eight weeks there was no significant difference (P > 0.05) in survival among treatments which averaged 95% overall. The average weight (g) and specific growth rate (gain in g/d) of fish fed 0% BG (56.5 and 0.90, respectively) and 15% BG (53.6 and 0.84) were statistically similar, although were both significantly greater (P ≤ 0.05) than for fish fed 30% BG (48.7 and 0.76) and 30% BGwAA (43.3 and 0.65), with 30% BG being larger than those fed 30% BGwAA. Feed conversion ratio (FCR) was significantly lower (more efficient) for fish fed 0% BG (1.14) than for both 30% BG (1.41) and 30% BGwAA (1.54). FCR for 15% BG (1.32) was smaller than fish fed 30% BGwAA, but not different from the other diets.

BG inclusion rates between 15 and 30% produced growth reduction and decreased FCR, and also indicate reduced palatability in the 30% BGwAA diet. Based on these data, inclusion rates up to 15% resulted in acceptable growth and FCR of juvenile tilapia. The utilization of locally sourced BG may be one step toward lowering production costs in aquaponic production, while also adding to the popular sustainability aspect.