Effect of Oxygen Management on Culture Performance of Channel Catfish in Earthen Ponds

—Aeration allows for higher feeding rates and increased production of channel catfish Ictalurus punctatus in intensive and semi-intensive aquaculture systems. However, the effect of specific dissolved oxygen (DO) concentrations on various production parameters remains unknown. The purpose of this 2-year study was to determine the effect of daily minimum DO concentration on channel catfish production. Six 0.1-ha ponds were each equipped with three 0.37-kW (0.5-hp) aerators and one 0.37-kW circulator. Dissolved oxygen concentrations were monitored and recorded with a commercial oxygen monitor that also controlled aeration. During both years, aeration in the high-oxygen treatment was initiated when the DO concentration dropped below 5.0 mg/L (mean, 64% saturation from May to September); aeration in the low-oxygen treatment was initiated when the DO concentration dropped below 2.5 mg/L (32% saturation; 2001) or 1.5 mg/L (19% saturation; 2002). The minimum DO concentrations resulting from this aeration protocol differed somewhat from aerator set points. In the low-oxygen treatment, delaying aeration until the DO concentration dropped below 2.5 mg/L reduced feed consumption by 6% relative to the highoxygen treatment. Other production parameters were not significantly different. In 2002, when aeration was delayed until the DO concentration dropped below 1.5 mg/L, the low-oxygen treatment group exhibited reductions in food consumption (45% less than consumption by the high-oxygen treatment), average fish weight (31% less), and net production (54% less). Even at the high feeding rates of 2002 (maximum of 680 kg · ha21 · d21; 44,066 kg/ha total in one pond), other water quality variables were acceptable. Net production in the high-oxygen treatment in 2002 averaged 23,547 kg/ha, a potential record for channel catfish in earthen ponds. Neither the feed conversion ratio nor survival was significantly different between treatments in either year. While these results cannot be directly extrapolated to large commercial ponds, it appears that increased aeration may increase production well above current commercial levels. During the past 30 years, average production rates of channel catfish Ictalurus punctatus in commercial ponds have increased from 1,130 kg/ha (1,000 lb/acre) to 3,400–6,800 kg/ha (3,000–6,000 lb/acre). Some individual farmers are producing as much as 13,608 kg/ha (12,000 lb/acre) on a wholefarm basis (George Smelley, Harvest Select Catfish, personal communication). This increase in production is due largely to the higher stocking and feeding rates made possible by increased aeration. Swingle (1959) recommended a maximum safe feeding rate of 34 kg · ha21 · d21 in unaerated ponds. At this feeding rate, dissolved oxygen (DO) provided by wind action and photosynthesis of the algal bloom is normally sufficient to meet the oxygen demands of the fish, the bloom, and the sediment, and emergency mechanical aeration is rare* Corresponding author: [email protected] Received November 9, 2004; accepted March 30, 2005 Published online August 1, 2005 ly needed to keep the fish alive through the night (Tucker et al. 1979). Tucker and Boyd (1978) suggested that 2,500–3,000 kg/ha of channel catfish may be produced annually in unaerated ponds without serious risk of oxygen depletion. As farmers increased fish stocking and feeding rates in an effort to grow more fish, problems with low DO concentrations increased in frequency and severity and emergency aeration was required more frequently (Tucker et al. 1979; Boyd et al. 1980). When most ponds on a farm required emergency aeration on a nightly basis (in the late 1970s and early 1980s), farmers permanently installed more-efficient electric aerators in each pond (Busch et al. 1984). These aerators are normally activated at night or in response to periodic DO measurements and are turned off in the morning when the DO concentrations begin to increase from photosynthesis. Channel catfish feeding and production rates have increased approximately in proportion to aeration rate. Increased aeration reduces the frequency and magnitude of oxygen depletion events, al-