The IPR needs emergency back-up systems in case of electrical disruptions or mechanical failures. A backup blower is recommended in case of blower failure.
In addition, the two blowers can be equipped with a pressure sensor that will turn on the backup blower in the event of a failure.
Sensors can be purchased that will sense not only power failures but air pressure loss (in the case of a cracked air-manifold).
These sensors can be attached to phone dialers which will call managers and alert them to problems and can automatically trigger emergency generators or oxygen supply systems.
A simple oxygen supply system can be constructed using cylinders of bottled oxygen connected to a normally-closed electric solenoid valve that opens if electrical power is interrupted.
High-pressure tubing leads from the cylinders to each raceway and is delivered through milli-pore tubing in the bottom of each raceway, similar to a hauling tank system.
Flow regulators control the volume of oxygen delivered and must be adjusted depending on the biomass of fish in the raceways.
Typically a single cylinder of oxygen will maintain a raceway for several hours. This system is also used to maintain adequate oxygen supplies during therapeutic bath treatments for disease Species and stocking rates.
To date, species that have been successfully cultured in IPRs include: channel, blue, and hybrid catfish; trout, striped bass and its hybrids, yellow perch, bluegill, and tilapia. Probably any species that tolerates flowing water can be cultured in an IPR.
Channel catfish and Nile tilapia have been successfully polycultured in the IPR. In one experiment tilapia were mixed in the IPR at a 1:10 ratio with catfish. In other experiments tilapia were isolated in a separate section of the IPR behind the catfish and were not fed, under the assumption that they would eat any uneaten catfish feed, catfish wastes, and plankton. The tilapia grew well in both these experiments.
Blue catfish and channel X blue hybrid catfish did not perform as well in the IPR as channel catfish in experiments at Auburn University. However, producers in more northern climates have reported success in culturing these in raceways. These observations may indicate more about the temperature preference of the blue catfish than about the culture system.
Stocking rates for most of these species have varied between 9 and 15 fish per cubic foot of effective culture volume. At least in the case of catfish, no difference in growth or food conversion has been found between stocking at 9 or 14 fish per cubic foot. From an economic standpoint, the high stocking rates of the IPR are probably necessary to offset the cost of construction and operation.
Finally, it is important to remember that stocking densities must be balanced with pond size. In open-pond catfish production it is common to stock 6,000 or more fish per surface acre but expect to harvest only 3,500 to 4,000 pounds of catfish per year.
In cages, catfish are normally stocked at only 1,500 to 2,000 fish per surface acre (unless aeration is supplied), and all the fish are harvested in a given year. In the case of the IPR, it is recommended to stock no more than 6,000 fish per acre and expect to harvest all of the fish (see economics section) in a given year.
As a note of interest, several species of freshwater mussels have also been cultured behind catfish in the IPR in an attempt to reduce effluent wastes. The mussels were somewhat effective at reducing solid wastes in the effluent, and some species of mussels showed significant growth under these conditions.
This research may have implications for the culture of freshwater mussels (the shells of these species are used as nuclei for cultured pearls) or in the culture of other shellfish species in brackish or marine environments.
Feeding:
Feeding rates (percent body weight per day) and times depend more on species cultured than on the culture system. For information on feeding rates and time of feeding, check other SRAC literature on specific species. Floating feed is recommended for the IPR, because the manager can see fish eat and determine if any feed is being wasted or uneaten. The IPR does allow the use of sinking feeds, including medicated feed if necessary.
Traditional raceway culture has often utilized demand or automatic feeders. Research on catfish in the IPR has shown that demand feeders work well. In fact, with catfish and tilapia there were no differences in growth or feed conversion using demand feeders as compared with twice a day hand feeding.
Fish cultured in raceways have better feed conversions than fish grown in open ponds with the possible exception of tilapia. This is also true of the IPR. In 5 years of research on catfish and tilapia, the average feed conversion ratio (FCR) was 1.45:1 (pounds feed fed to pounds of fish produced).
Finally, because of the high density and lack of any natural foods, raceway culture depends on high quality complete diets. In IPR research on catfish and tilapia at Auburn University, a 36 percent protein commercially available diet was fed in most experiments, rather than the 32 percent protein diet that is commonly used in pond culture. Most cage producers also use a 36 percent protein complete diet.
Disease treatments:
Disease treatments in raceways are usually drip treatments. The therapeutant is dripped into the incoming water, and a specific concentration is maintained for a certain period of time, usually 1 hour. Problems with this method are that the concentration is difficult to maintain, a large amount of therapeutant is used, and the rapeutant is released into the environment with the discharge.
In the IPR, the emergency oxygen system can be used to conduct therapeutic bath treatments. In this case the air blower is turned off and the emergency oxygen supply system is used. With no water flow the raceway is treated as a tank of known volume.
The therapeutant is mixed into the raceway at the prescribed concentration and maintained for the recommended time period. DO concentrations should be checked and the oxygen supply regulated during the treatment.
After treatment the air blower is turned on, and the therapeutant is flushed out of the raceway within a few minutes. Obvious advantages of this system are that less the rapeutant is used, a more precise concentration is achieved, and if problems occur the treatment can be terminated quickly.
Authors:
Michael P. Masser and Andrew Lazur
