Floating in pond raceways have potential to improve presentation of feed to the fish, assure good oxygen concentrations for growth, improve feed efficiency, improve inventory control, minimize predation, facilitate management of disease, and increase access for harvest. This work is oriented to the small farm with existing impoundments that are not drained.
Following an initial assessment of a floating raceway for production of fingerling largemouth bass, a suspended design with integrated floatation was scaled up for greater production potential (photo). These raceways feature a uniform square cross section and hard flat bottom such that workers in waders can crowd, grade, and harvest the fish. Though the entire unit is 9.75m long, rearing space occupied by fish is 9.5m3 (21’x4’x4’). The device moving water is a grid airlift with air from a 0.5 hp regenerative blower at the head of the raceway. Sustained measured flow exceeds 4000 Lpm for a corresponding exchange rate in excess of 20/hr. Though carrying capacity has not been empirically determined, a ton of fish would correspond to 66 kg/m3 (6 lb/ft3) and a loading rate of 0.24 kg/L/min. It is estimated a ton of catfish @ 454g/fish would remove about 2 mg/L dissolved oxygen at 30°C (Table).
This design may be constructed on-farm with material costs for the raceway, floatation, air blower, screens, and grid airlift estimated to be about $2,500. The system can be configured for both fingerling production and grow out.