Catfish production practice/technology has changed substantially within the last four decades, as fish farmers are driven to intensify production. Average pond electrical aeration in southern catfish ponds increased (1982 to 2020) from 1.87 kW/ha (1 hp/acre) to 2.25 kW/ha (4,2 hp/acre), with a significant percentage (in 2010) using in excess of 7.9 kW/ha (3.8 hp/acre). Efforts at Clemson University, from 1996-2001, focused on intensification of fish culture and reduction in water use though application of a “high-rate algal pond’ entitled the Partitioned Aquaculture System (PAS) The original 0.33-2.0-acre PAS prototypes use slowly rotating paddlewheels to circulate water through shallow (2-ft) channelized ponds (95% of area), increasing algal photosynthesis and enhancing treatment rate of nitrogenous waste (NH3). Catfish are confined to 5% of area in high density raceways (6.0 lb/ft3) at mixing/aeration energy of 4.5 hp/acre. At the time, conventional catfish ponds (CP) were utilizing 100% of pond volume/area for fish culture at aeration energy of 2.0 hp/acre. The Split-Pond (SP), developed at the National Warm-water Aquaculture Center (NWAC) beginning in 2002, represents a lower cost adaptation of Clemson’s PAS. Prototype SPs at NWAC range in size from 5.0-7.0 acres utilizing 5.7-7.0 hp/acre mixing/aeration, with fish culture confined to 20-25% of surface area with 75-80% devoted to waste treatment. NWAC also reported on evaluation of prototype 4.0 acre intensively aerated catfish ponds (IP), utilizing 100% of pond volume for fish culture at elevated aeration energy levels of 8.0 hp/acre.
A performance analysis provided on prototype CP, SP and IP and PAS units suggested fish carrying-capacity in CP of 5,000-7,500 lb/acre, PAS at 15,000-18,000 lb/acre, SP at 12,330-19,000 lb/acre and IP at 9,200-18,245 lb/acre. Average/maximum sustained feed loading was 100/150 lb/acre-day for CP, 160/250 for PAS, 110/280 for SP, and 84/270 for IP. The PAS, SP and IP are highly photosynthetic (3.3-4.3xCP) however, the PAS provides the highest degree of net photosynthesis and ammonia removal. The PAS aggressively re-mineralizes settled algal biomass which is recaptured as additional algal biomass. The SP aggressively removes algal biomass (via sedimentation in the waste treatment zone, WTZ) and promotes nitrification in a WTZ anoxic layer. The IP provides a higher degree of settled algal storage in the sediment. The IP is more subject to sporadic release of sediment ammonia driven by climatic changes, whereas the PAS and SP provide more consistent operator control of oxygen and nitrogen flux.
Currently 7% of U.S. catfish production is from SP with 33% in IP. The PAS was designed to provide maximum nitrogen treatment via optimized algal photosynthesis. Capital costs for PAS are similar to in-pond raceways at $22,630/acre with a breakeven catfish production cost of $1.32/lb. In contrast, SP capital cost is projected at $6,904/acre with BEC of $0.92/lb and IP at $8,380/acre with BEC of $0.93/lb. The SP provides 78% of the net photosynthetic capability of the PAS at 70% of the production cost/lb. The IP provides 87% of the net photosynthesis at 69% of the production cost/lb. The IP requires minimal modification of existing ponds, the major cost being addition/maintenance of aerators. The SP requires substantial modification of existing ponds but provides more consistent/reliable treatment of ammonia nitrogen. SP provide advantages in fish feeding/harvesting and predator control. Fish farmers have reported excessive accumulation of ammonia (3-6 ppm) in IP, particularly during late summer to winter months.