Effects of dietary protein content on hybrid tilapia (Oreochromis aureus×O. niloticus) performance, common microbial off-flavor compounds, and water quality dynamics in an outdoor biofloc technology production system

Authors: Green, Bartholomew - Bart; Rawles, Steven - Steve; Schrader, Kevin; GAYLORD, T. GIBSON - U.S. FISH AND WILDLIFE SERVICE; McEntire, Matthew - Matt

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2019
Publication Date: 2/5/2019
Citation: Green, B.W., Rawles, S.D., Schrader, K.K., Gaylord, T.G., McEntire, M.E. 2019. Effects of dietary protein content on hybrid tilapia (Oreochromis aureus×O. niloticus) performance, common microbial off-flavor compounds, and water quality dynamics in an outdoor biofloc technology production system. Aquaculture. 503:571-582. https://doi.org/10.1016/j.aquaculture.2019.01.034.
DOI: https://doi.org/10.1016/j.aquaculture.2019.01.034

Interpretive Summary: The biofloc technology production system is a production intensifying management strategy used primarily for culturing tilapia and marine shrimp. Because tilapia grown in the biofloc technology production system can consume the biofloc (a complex of algae, micro-crustaceans, and microbial grazers closely associated with particulate organic matter), it should be possible to optimize formulated diet protein content to account for nutrition derived from consuming biofloc. We conducted a 5-month experiment in an outdoor biofloc technology production system to determine how feeding hybrid tilapia with diets formulated to contain 22.5%, 27.7% or 32.3% digestible protein affected fish production and water quality. Market size tilapia (1 lb/fish) were produced with all diets, but the size distribution at harvest of tilapia fed the 22.5% protein diet were skewed towards smaller sizes compared to fish fed the other diets. Our results suggest that diet digestible protein content can be reduced from 32.3% to 27.7%, but not to 22.5% for hybrid tilapia grown to market size in the biofloc technology production system. The 5% reduction in protein content of the diet will result in cost savings.

Technical Abstract: Because tilapia grown in the biofloc technology production system can consume the biofloc, it should be possible to optimize formulated diet protein content to account for nutrition derived from consuming biofloc. The present study, conducted in an outdoor biofloc technology production system, evaluated impacts on fish production indices and water quality dynamics of feeding hybrid tilapia (Oreochromis aureus x O. niloticus) fed diets formulated to contain 22.5% to 32.3% intact digestible protein (DP) and 6% lipid. Fingerling (32.2 +/- 10.1g/fish) were stocked in tanks (18.6m2; 16.6m3) in May 2016 at 25/m2 (29/m3) and grown for 5 months to market size. At harvest, fish fed the 22.5% DP diet were significantly smaller (518g/fish) and had significantly higher feed conversion (1.5) than those fed the higher DP diets (553-564g/fish and 1.4, respectively). Feed nitrogen input and nitrification rate increased linearly with increased DP. Results of this study suggest that by using ideal protein theory to formulate diets supplemented with the first four limiting amino acids (LYS, MET, THR, ILE) DP can be reduced from 32.3% to 27.7% without adversely affecting hybrid tilapia productivity indices. Market size distributions, nutrient retention, off-flavor, and pond water quality dynamics in relation to diet DP also are discussed.