Impact of dietary phytase on tilapia performance and biofloc water quality

We tested the hypothesis that the fate of dietary phosphorus will not differ among a dicalcium phosphate-free practical diet treated with 6-phytase (3000 FTU/kg; Quantum Blue™; P-F + Phy), and positive (C) and negative (P-F) control practical diets when fed to hybrid tilapia (Oreochromis aureus x O. niloticus; 29.8 g initial weight) stocked at 29 fish/m3 and grown for 5 months to market size (454 g/fish) in outdoor biofloc production system tanks (16.6 m3). The ideal protein diets were formulated to contain 27.7% digestible protein and 4% lipid from practical ingredients and were extruded commercially. Final weights (467–494 g), weight gains (1636-1723%), and average daily intake (2.10–2.18%) did not differ for fish fed the P-F + Phy or C diets; however, these metrics were significantly lower in the P-F diet treatment. There were fewer market size fish (46.8–54.7%), feed conversion ratios were poorer (1.59–1.61), and intraperitoneal fat contents (6.96–7.40%) were higher for fish fed the phosphorus-free diets compared to the C diet (65.3%, 1.46, 5.90%). Geosmin, as compared to 2-methylisoborneol, was considered the more relevant off-flavor compound and fillet concentrations were higher than those for 2-methylisoborneol, but concentrations present of each compound were unlikely to cause “earthy” or “musty” off-flavors. Accumulation rates of soluble reactive phosphorus, organic phosphorus, and total phosphorus in tanks fed the phosphorus-free were diets nearly half those observed for the C diet while phosphorus loading from feed was 37.7% lower. •Phytase top coating of feed substituted for diet inorganic P in tilapia biofloc.•Biofloc consumption by tilapia contributes to mineral nutrition.•Phytase treated feed reduced environmental P loading by 38%.•Phytase treated feed reduced P accumulation rate in culture water by nearly 50%.