Commercial Prawn Production
The three phases of freshwater prawn culture are hatchery, nursery, and pond growout. Initial planning and operation of a prawn production enterprise should temporarily forego the hatchery phase, and possibly the nursery phase. Although the hatchery and nursery phases are comparatively shorter, future investment of time and money should be based on achieving success repeatedly in the pond growout stage. Any plans for development of a nursery and possibly hatchery phases of production should be approached with careful planning. Nursed juveniles for stocking into growout ponds can be purchased from a supplier.
Production of juvenile freshwater prawns for stocking into growout ponds begins with maintenance of a healthy broodstock population. In temperate climates, prawn broodstock are generall selected from the crop harvested from ponds and then transferred to tanks or raceways located within a temperature-controlled building. Water temperature for broodstock holding should range between 77 and 82.4º F (25 and 28oC). Broodstock are generally stocked at a density of 19 prawns per liter in a ratio of 10 females to 2 to 3 males. Tanks or raceways that hold broodstock should be equipped with structures that will allow maximum use of the entire water column.
“Clearwater” (having minimal algal growth) recirculating systems containing water at a temperature of 82.4 to 86º F (28 to 30º C) and a salinity of 12-15 ppt are recommended for larval culture. Use of recirculating systems provides for efficient use of water and reduction of heating costs. Water in the larval culture system is pumped from a collecting reservoir (sump) through a sand filter, then through an ultraviolet light unit and a biological filter before it enters into the tank where the larvae are cultured.
After the metamorphosis through the 11 larval stages has been completed, larvae then metamorphose into postlarvae (PLs). After a significant proportion of larvae (25-33%) has transformed to postlarvae, the remaining larvae are transferred to another culture tank so that the postlarvae can be collected for transfer to the nursery phase of culture. Generally, survival at termination of the hatchery phase of culture ranges from 40 to 80%.
The nursery stage of culture is the period when juveniles are produced for stocking into production ponds. This management practice is included to increase an otherwise time-restricted growing season due to growth limiting and lethal water temperatures in production ponds. A by-product of this management approach is a larger animal for stocking into growout ponds.
Nursery culture is generally conducted in tanks within climate-controlled buildings. Water temperatures should range between 78.8 to 82.4º F (25 to 28º C). The design of a nursery facility will vary according to the respective need for insulation to maintain desired water temperature. To conserve water and heat, water recirculation systems are recommended. Flow-through systems equipped with heaters may also be used, but practicality is dependent on availability, temperature, and cost of the water. The use of recirculating systems will require the activation and maintenance of populations of nitrifying bacteria (biological filters) to transform toxic ammonia to non-toxic nitrate. No pesticides should be used in or near (at least 100 yards) a nursery facility.
The stocking density for nursery tanks should range from 12 to 23 postlarvae/gal. Stocking density can also be based upon the amount of substrate present in the nursery tank, 20-40/ft2 of surface area of substrate. The addition of substrate is critical. A 25% increase in survival is realized after 60 days of nursery culture if substrate is provided.
Typically, a nursery phase of 45-60 days results in a population of juvenile prawns with a mean weight of 0.3 g and survival that ranges from 55 to 80%. Survival varies according to stocking density, amount of substrate used, feeding rate, water quality, duration of the phase, and numerous other variables.
Size grading of juveniles from a nursery-grown population prior to stocking into production ponds is an effective method to increase individual mean harvest weight and total yield. Grading separates the fast growing prawns from the slow growing ones, a size disparity that is the product of the typical social hierarchy that develops among males during the nursery phase.
A feeding-fertilization program before stocking is recommended to discourage growth of common problem weeds. After the pond is filled with water, apply an inorganic fertilizer, 10-34-0 or 13-38-0, at a rate of 1/2 gallon per surface acre. To stimulate natural food organisms, make a one-time application of cottonseed meal or sinking catfish feed at 200 to 300 pounds per acre. Continue fertilization with a catfish feed or meal at a rate of 15 to 20 pounds per acre on alternate days until application of formulated feed begins.
Size graded juveniles (0.1 to 0.3 g) have been commonly stocked at 10,000 to 20,000 per acre. Lower stocking densities will yield comparatively lower total harvested weight per acre but higher weight per prawn. The duration of the growout period is dependent on the water temperature of the ponds and generally ranges from 120 to 150 days in central Mississippi.
MSU Publications & Information
Other Freshwater Prawns Information