Raceways used for aquaculture are rectangular shaped tanks, chutes or earthen structures with a continuous source of flow-through water introduced at one of the short sides and exiting at the opposite end. The temperature, and general quality of the water source must be compatible with the species being raised and the flow must be great enough to maintain water quality and carry waste out in accordance with the number of fish being raised. Many raceway systems depend on high-flow rate springs and do not reuse the water after it exits. They also depend on pelleted feed. As a result, raceway systems are generally considered to be of low sustainability. However, the in-pond raceway system mitigates the low sustainability of aquaculture raceways by recirculating water and providing for production of an extensively reared fish crop in the pond area not occupied by the raceways.
In-pond raceway system design consists of fixed parallel raceways constructed in one corner of a traditional earthen pond with a center baffle to provide for a continuous circulation pattern around the pond and through the raceways. Low speed paddlewheels provide a constant current through the raceways. The raceways are stocked at high density with a suitable fish species such as channel catfish, which are fed pelleted feed. As water flows through the raceways, the waste products generated in the raceways are carried into the open pond area where they are processed naturally and actually stimulate the production of organisms that can become food for another fish species, such as paddlefish.
In a trial beginning in the spring of 2008, 700 paddlefish of average weight 328g were stocked into the open water area of a 2.43 ha (6 acre) pond into which the above described in-pond raceway system was installed and channel catfish were the primary species. After 675 days, the paddlefish were seine harvested. Total yield was 2406 kg (5293 lbs) and average individual fish weight was 4.0 kg (8.8 lbs). Survival was 85.9%. For paddlefish production, this method has several advantages over the open-pond method of polyculture. First, the paddlefish are not incidentally handled during catfish harvest, avoiding stress of the paddlefish and the cost of separating the paddlefish from the catfish. Second, the paddlefish are not exposed to predation by large catfish in the pond. Lastly, female paddlefish can be left in the pond until maturity for caviar harvest assuming uninterrupted good water quality. Hence, this method can be used for both paddlefish meat and caviar production