Before introduction of catfish fry, stock juvenile prawns at a rate of 3,000 to 5,000 per acre. Stock catfish fry at a density to insure that they will pass through a 1-inch-mesh seine used to harvest the prawns at the end of the growing season.
Although polyculture of prawns and a mixed population of channel catfish has been successfully demonstrated, logistical problems arising from efficient separation of the two crops is inherent in this management practice. Moreover, when harvest of prawns is imminent due to cold water temperatures, catfish may not be a harvestable crop due to an “off flavor” characteristic.
Polyculture of channel catfish and freshwater prawns may be best achieved through cage culture of the fish. Recently, a scheme for intercropping of freshwater prawns and red swamp crawfish was developed and evaluated (Figure 3).
Intercropping is the culture of two species that are stocked at different times of the year with little, if any, overlap of their growth and harvest seasons. Intercropping provides for a number of benefits that include:
- Minimizing competition for resources;
- Avoiding potential problems of species separation during or after harvest; and
- Spreading fixed costs of a production unit (pond) throughout the calendar year.
Adult mature crawfish are stocked at a rate of 3,600 per acre in late June or early July. Juvenile prawns are stocked at a density of 16,000 per acre in late May and harvested from August through early October. In late February, seine harvest of the crawfish begins and continues through late June before stocking of new adult crawfish.
Prawns are small enough to pass through the mesh of the seine used to harvest crawfish during the May-June overlap period. Other intercropping scenarios involving such species as bait minnows, tilapia and other fish species may be possible, but to date no research has been conducted in the Southeast.
Processing and marketing:
Marketing studies strongly suggest that a “heads off” product should be avoided and that a specific market niche for whole freshwater prawns needs to be identified and carefully developed.
To establish year-round distribution of this seasonal product, freezing, preferably individually quick frozen (IQF), is an attractive form of processing, and recent research has demonstrated its efficacy and potential. Block frozen is an alternative method of processing for long-term distribution.
Recent research at the Mississippi Agriculture and Forestry Experiment Station suggests that adult freshwater prawns can be successfully live hauled for at least 24 hours, at a density of 0.5 pound per gallon, with little mortality and no observed effect on exterior quality of the product.
Transport under these conditions requires good aeration. Distribution of prawns on “shelves” stacked vertically within the water column assists in avoiding mortality due to crowding and localized poor water quality. Use of holding water with a comparatively cool temperature (68 to 72°F) minimized incidence of water quality problems and injury by reducing the activity level of the prawns.
Based on an average feed cost of $250 to $300 per ton, a seedstock cost of $65 per 1,000 juveniles, a 2.5 to 1 feed conversion, expected mean yields of 1,000 pounds per acre, and a pond bank selling price of $4.25 per pound, the expected return can be as high as $2,000 to $2,500 per acre. Revenue and ultimate profitability depend on the type of market that is used.
This estimated return does not include labor costs or other variable costs that differ greatly from operation to operation. Some thorough economic evaluations that incorporate annual ownership and operating costs under different scenarios for a synthesized firm of 43 acres, having 10.25 acres of water surface in production, are provided in Mississippi Agriculture and Forestry Experiment Station Bulletin 985, available from the Department of Agricultural Economics, Mississippi State University.
Louis R. D’Abramo and Martin W. Brunson