Submitted to: NWAC (National Warmwater Aquaculture Center) Aquaculture Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: 11/10/2003
Publication Date: 7/1/2004
Citation: Torrans, E.L. 2004. Effect of (Minimum) D.O. Concentration on Channel Catfish. NWAC (National Warmwater Aquaculture Center) Aquaculture Newsletter. 7(1):10-11. Interpretive Summary: Farmers have long known that increased aeration allows them feed more and grow more fish. However, since we still do not know how specific dissolved oxygen (D.O.) concentrations affect channel catfish growth and production, every farm has its own oxygen management plan, most based largely on keeping the fish alive over night. The purpose of this two-year study was to determine the effect of daily minimum oxygen concentration on channel catfish food consumption, growth, production, and food conversion. Dissolved oxygen (D.O.) was monitored and controlled in six quarter-acre ponds. The D.O. was allowed to drop to either 5.0 ppm (high oxygen control treatment both years), 2.5 ppm (low oxygen treatment in 2001), or 1.5 ppm (low oxygen treatment in 2002) before aeration was started. Fish were fed floating feed once daily as much as they would eat. Ponds were harvested at the end of each growing season. In this study there was no benefit to initiating aeration before the D.O. concentration dropped to 2.5 ppm. Net production was not increased with D.O. maintained above that concentration, but 160% more aeration was required. However, if the D.O. was allowed to decrease to 1.5 ppm before aeration was initiated, feed consumption, fish growth and net production all declined by 30% or more, even though visible signs of stress (fish at the surface or crowded near the aerators) were not observed. Fish in the high oxygen treatment (in 2002) consumed 37,296 lbs of feed/acre, compared to 20,482 lbs/acre in the low oxygen treatment. This greater food consumption meant the difference between fingerlings (stocked at 81 lbs/1000) reaching market size (1.67 lbs) in one season, instead of having sub-marketable fish (1.16 lbs) at the end of the growing season.
Technical Abstract: Farmers have long known that increased aeration allows them feed more and grow more fish. However, since we still do not know how specific D.O. concentrations affect various production parameters, every farm has its own oxygen management plan, most based largely on keeping the fish alive over night. The purpose of this study was to determine the effect of daily minimum oxygen concentration on channel catfish food consumption, growth, production, and food conversion. Six quarter-acre ponds were each equipped with three ½-hp aerators and one ½-hp circulator. Dissolved oxygen (D.O.) and temperature were continuously monitored with a commercial oxygen monitor, which also controlled aeration. Aeration was initiated in the 'high oxygen' treatment both years when the D.O. dropped below 5.0 mg/L; aeration was initiated in the 'low oxygen' treatment when the D.O. dropped below 2.5 mg/L (2001 study) or 1.5 mg/L (2002 study). Fish were fed daily to apparent satiation with floating feed. Ponds were harvested at the end of each growing season. Minimum D.O. in the high oxygen treatment averaged over 4.3 mg/l from June-September of both years; minimum D.O. in the low oxygen treatment averaged 2.6 mg/L in 2001 and 1.7 mg/L in 2002. Maintaining these lower oxygen concentrations required significantly less aeration; aeration time in the low oxygen treatments were reduced 62% in 2001 and 84% in 2002 (P<0.05 both years). Delaying aeration until the D.O. dropped to 2.5 mg/L (in 2001) had little impact on production parameters. Feed consumption decreased by 6.3% (P<0.05), but all other parameters were similar. However, delaying aeration until the D.O. dropped to 1.5 mg/L (in 2002) had major impacts: average fish weight was 30.5% less; net production was 54.0% less (P<0.05) and feed consumption was 45.1% less (P<0.05) than the high oxygen treatment. Feed conversion was not significantly affected by reduced oxygen. It appears that if feed was consumed, it was converted with similar efficiency. Even at the high feeding rates of 2002 (up to 600 lbs/acre/day; 38,860 total lbs/acre in one pond), no critical water quality parameters were observed.