Effect of dietary protein on hybrid tilapia production in a biofloc technology system

Authors: Green, Bartholomew - Bart; Rawles, Steven - Steve; Schrader, Kevin; Webster, Carl; GAYLORD, T. GIBSON - Us Fish And Wildlife Service; McEntire, Matthew - Matt

Submitted to: World Aquaculture Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/5/2017
Publication Date: 6/26/2017
Citation: Green, B.W., Rawles, S.D., Schrader, K., Webster, C.D., Gaylord, T., McEntire, M.E. 2017. Effect of dietary protein on hybrid tilapia production in a biofloc technology system [abstract]. World Aquaculture 2017, June 26-30, Cape Town, South Africa. p. 233.

Interpretive Summary:

Technical Abstract: In an outdoor biofloc technology (BFT) production system a complex of living organisms that includes phytoplankton, zooplankton, ciliates, nematodes, bacteria, all closely associated with particulate organic matter, is maintained suspended in the water column by continuous aeration. Tilapia grown in the BFT system can derive nutrition by consuming the biofloc, and because of this some researchers advocate reducing formulated ration protein content. Using the ratios and concentrations of essential amino acids in hybrid tilapia muscle, i.e., the ideal protein model we selected, as targets for optimizing diet formulation, we formulated three diets based on digestible nutrient content of feed ingredients and supplemented the formula with essential amino acids to meet the target levels suggested by the muscle profile. Diets were formulated to contain 22.5%, 27.7%, and 32.3% intact digestible protein and 6% lipid.Hybrid tilapia (Oreochromis aureus female x O. niloticus male; 32.2 g/fish) were stocked at 25 fish/m2 into each of nine outdoor 18.6-m2 BFT system production tanks and grown for 146 d. Fish were fed their respective diets to apparent satiation twice daily.Fish consumed each diet equally well. Feed consumption during the peak feeding period (28 Jun-8 Oct) and the entire experiment did not differ significantly and averaged 194.4 g/m3/d and 22.2 kg/m3, respectively. Production varied among diets, with significant differences between the 22.5% and 27.7% protein diets, with the 32.3% protein diet being intermediate. Mean final weights were 517.9, 564.5, and 552.6 g/fish for the low to high protein level, respectively. Respective gross fish yields were 14.0, 15.6, and 14.9 kg/m3. Feed conversion ratio (FCR) was significantly lower for the 22.5% protein diet (1.5) compared to an FCR of 1.3 for the other two diets. Survival did not differ significantly and averaged 98.8%. Hepatosomatic index decreased linearly and muscle ratio increased linearly in response to increasing dietary protein. Intraperitoneal fat did not differ significantly among dietary protein. Geosmin and 2-methylisoborneol (MIB) were detected in fillets sampled at harvest from fish from each treatment tank. Only one replicate tank each from the 22.5% and 32.3% protein treatments contained fish with geosmin and MIB concentrations that likely would be designated as being “on-flavor” when evaluated by trained processing plant flavor testers. The source of the off-flavor remains to be determined. Results of this experiment suggest that diet protein can be reduced by 5% to 27.7% digestible protein with no adverse effect on production, but further reduction causes a loss in productivity, but an economic evaluation is needed.