LAUSR

Abstract Since excreted feed nitrogen is bio-transformed efficiently in a fully functional mixotrophic biofloc technology production system, re-using this biofloc water over multiple production cycles should be beneficial. The present study, conducted in an outdoor biofloc technology production system, evaluated impacts on fish production characteristics and mineral status, common microbial off-flavors, and water quality dynamics for channel catfish (Ictalurus punctatus) reared in one-year-old waters with low or high total suspended solids used previously for two consecutive catfish biofloc studies or in unused (new) water. Total suspended solids were maintained at 300 to 400 mg/L in the unused and low total suspended solids used water treatments and allowed to accumulate in the high total suspended solids used water treatment. Tanks (18.6 m2, 15.7 m3) were stocked with fingerlings (47.5 ± 0.8 g/fish) at 13.5 fish/m2 (16 fish/m3) and grown for 181 days. Channel catfish production characteristics did not differ significantly among treatments. Overall, gross fish yield averaged 10.2 kg/m3 and fish averaged 642 g/fish. Nitrate accumulation rate was affected by total suspended solids concentration with a significant reduction observed at the highest discharge of solids from the system, suggesting wash-out of nitrifiers. Treatment effects on water quality dynamics, macro- and trace-mineral status of water, feed, and fish, 2-methylisoborneol and geosmin off-flavors and associated phytoplankton populations also are discussed. Results of this study suggest that one-year-old biofloc water can be used without adverse impact for a second year of channel catfish production in the biofloc system.