There are four basic types of fish culture systems: open-ponds, cages, raceways, and recirculating systems. Each system has advantages and disadvantages in culture performance, water quality, ease of management, and economic returns.
In fish culture, traditional raceways are enclosed channel systems with relatively high rates of moving or flowing water. This high rate of water movement gives raceway systems distinct advantages over the other culture systems. Advantages of raceways can include:
- higher stocking densities
- improved water quality
- reduced manpower
- ease of feeding
- ease of grading
- ease of harvest
- precise disease treatments
- collection of fish wastes
- less off-flavor
Most raceway operators believe they have more control over their fish production, and they see this as the major benefit of raceway culture. This control is achieved only if flow rate and water quality are relatively stable over time.
Stocking densities for raceways are usually higher than for other culture systems. Densities of 10 to 15 fish per cubic foot are not unusual for raceway systems. These high densities have distinct disadvantages including: more rapid disease spread, less reaction time when problems occur, and large volumes of effluent with dilute fish wastes.
In general, water cannot be economically pumped through raceways; it must flow through them by gravity. The need for large volumes of good quality water is the principal reason raceways have been limited to sites with large springs.
Most raceway culture in the U.S. is with coldwater species such as trout and is based around locations with high volume, cold springs, or creeks. A few raceway systems for warmwater species have been located at sites with warm geothermal springs.
Problems involving lack of water movement through cages in watershed ponds led to the development of air-lift pumps to move water through them. This in turn led to research on developing raceways that would float in a pond (or any body of water) and have a constant flow of water, supplied by air-lift pumps.
The idea was to develop a raceway system powered by air-lift pumps that could float in existing ponds and have some of the advantages of traditional raceways such as:
- higher fish densities,
- better water quality,
- waste collection,
- precise disease treatment, and
- better control over feeding, grading, harvest, etc.
In a pond, this system would also have the advantage of not discharging wastes into the public domain since the pond would act as reservoir and treatment system. The development of an air-lift driven In-Pond Raceway (IPR) began at Auburn University in 1991.
However, literature searches have revealed that systems of somewhat similar design or concept had been developed, and even patented, since the turn of the century.
Authors:
Michael P. Masser and Andrew Lazur
