One of the anticipated benefits of the IPR was to capture or reduce wastes from the system.
By doing this the IPR system would be more “environmentally friendly” and/or could produce more fish per acre, particularly when compared to cages in watershed ponds.
However, it should be noted that fish wastes are mostly soluble, and solids are almost neutrally buoyant and therefore difficult to settle.
If the pond utilized is large and the stocking density per acre low, it may not be necessary to practice waste reduction at all, since the pond should be able to absorb and decompose the waste effluent through natural cycles.
Several different low cost and low maintenance methods of trapping or reducing wastes from the IPR have been researched.
These have included settling basins, tube settlers, sand and synthetic mesh filters, plant and gravel biofilters, artificial wetlands, and filter-feeding species in polyculture.
The best methods appear to be polyculture with filter feeding species (see species and stocking rates section), and tube settlers (for the solids) coupled with some type of plant biofilter or artificial wetland outside of the raceway.
Actual costs of these waste reduction systems and their total impact on the pond environment have not been adequately evaluated.
Problems:
All culture systems have advantages and disadvantages. Like other high density raceway systems the IPR has problems related to disease, reaction time, and predators. Diseases, particularly bacterial diseases, are common in all high density systems, especially raceways, cages, and recirculating systems.
Bacterial diseases, particularly Enteric Septicemia of Catfish (ESC) and Columnaris, have been problematic with the IPR catfish research at Auburn University. Survival of catfish in IPR research has ranged from 65 to 98 percent, which is similar to cage research in the same pond. Tilapia survival has averaged around 97 percent; most of these losses have been due to escapement. Commercially operated IPRs have reported better overall survival.
Reaction time is another problem with the IPR as with other high density production systems. Backup systems, either generators or pure oxygen systems, are absolutely essential as power disruptions are inevitable. Since generators eventually run out of fuel and oxygen cylinders become depleted, electrical and/or pressure sensors with phone dialers are prudent components of these systems.
Predators, particularly birds, raccoons, and otters, are attracted to IPRs. The lids and mesh barriers around the inflows and outflows must be properly constructed and routinely maintained to exclude these persistent predators.
Economics
Cost of constructing an IPR system can vary greatly depending on the size and the materials used. The 16x4x4-foot IPR and dock system cost approximately $3,000 to build in 1994.
This construction cost does not include the air-blower or the backup oxygen system (included in the budget, see Table 1). If constructed properly, an IPR system should have a viable life of 5 to 10 years (5 years in budget, Table 1).
Examining the economics of any new system is always difficult, and the reader should be aware that these are only examples for comparison. Assumptions have been made in Table 1 in order to compare the IPR system with traditional open-pond or cage production systems.
In the example budgets presented, the data on production and labor costs are based on composites of actual data from research conducted on the IPR, cages, and open-ponds at Auburn University.
It should be noted that the IPR has been shown to have lower labor costs and better feed conversion when compared to the other two systems. However, the IPR has higher construction costs (not including pond construction), higher energy costs, and higher feed costs (if using a 36 percent protein feed for catfish).
In Table 1, the stocking rate is increased on a per acre basis for the IPR and decreased for cages (based on research and practical experience) as compared to open pond production. The feed budgeted is a 36 percent protein diet for the IPR and cages and a 32 percent protein for the open-pond.
Feed conversions are based on actual research data. In this comparison the IPR has the lowest breakeven costs and cages the highest. It should be noted that through evaluations of commercial catfish operations (SRAC - PESCAT Project) a 1-acre pond is too small, because of economies of scale, for economical catfish production.
Therefore, the breakeven cost is high in all of these hypothetical situations. Remember, these are only estimated budgets based on research data and should be used as guidelines for evaluation purposes only.
Authors:
Michael P. Masser and Andrew Lazur
