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

Given 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, common microbial off-flavors, and water quality dynamics for hybrid tilapia (Oreochromis aureus × O. niloticus) fed diets formulated to contain 22.5%, 27.7%, and 32.3% digestible protein (DP) and 6% lipid. Fingerlings (32.2 ± 10.1 g/fish) were stocked in tanks (18.6 m2; 16.6 m3) 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 (518 g/fish) and had significantly higher feed conversion (1.5) than those fed the higher DP diets (553–564 g/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) digestible protein can be reduced from 32.3% to 27.7% without adversely affecting hybrid tilapia productivity indices. Market size distributions, nutrient retention, 2-methylisoborneol and geosmin off-flavors, and pond water quality dynamics in relation to diet DP also are discussed.