SRAC Publication No. 484

VI July 1996 PR

Production of Freshwater Prawns in Ponds

Louis R. D’Abramo and Martin W. Brunson*

The final phase of freshwater important, and the soil must have ing. Ponds should have a mini- prawn () production is excellent water-retention qualities. mum depth of 2 to 3 feet at the grow-out of juveniles to adults for Well water of acceptable quality is shallow end and a maximum market as a food product. the preferred water source for depth of 3.5 to 5 feet at the deep Research in Mississippi, Kentucky raising freshwater prawns. Sur- end. The slope of the bottom and other southern states has face runoff water from rivers, should allow for rapid draining. demonstrated this can be a prof- streams and reservoirs can be You can obtain assistance in itable enterprise, and this publica- used, but quality and quantity can designing and laying out ponds tion provides guidelines for stock- be highly variable and subject to by contacting a local office of the ing and managing a freshwater uncontrollable change. The quali- Natural Resources Conservation prawn production pond. ty of the water source should be Service (formerly Soil Conserva- Unless you have a hatchery/nurs- evaluated before any site is select- tion Service). SRAC Publications ery, you must purchase juveniles ed. #100, 101, 102 and 103 provide for the pond grow-out phase. Locate ponds in areas that are not additional information on pond There are commercial hatcheries subject to periodic flooding. design and construction. in Texas, California and Mexico Before building ponds specifically Collect a soil sample from the that produce postlarvae and juve- for producing freshwater prawns, pond bottom to determine niles. The 1996 price is about $65 check the soil for the presence of whether lime is needed. Take soil per 1,000 juveniles. You can mini- pesticides. Prawns are sensitive to samples from about six different mize shipping costs if the hatch- many of the pesticides used on places in each area of the pond, eries are located within a 10- to row crops. Also, analyze the soil and mix them together to make a 14-hour driving distance of your for the presence of residual pesti- composite sample that is then air- grow-out facility. Otherwise, it is cides. Do not use ponds that are dried. Put the sample in a soil best to have the juveniles shipped subject to drift from agricultural sample box, available from your via plane, but this significantly sprays or to runoff water that county Extension agent, and send increases the cost. might contain pesticides. it to the state soil testing laborato- The surface area of grow-out ry in your state, typically operated Site selection and pond ponds ideally should range from 1 by the Cooperative Extension design to 5 acres, but larger ponds have Service, and request a lime been successfully used. The pond requirement test for a pond. There Ponds used for raising freshwater should be rectangular in shape to may be a small charge for this ser- prawns should have many of the facilitate distribution of feed vice. If the pH of the soil is less same basic features of ponds used across the entire surface area. The than 6.5, you must add agricultur- for the culture of channel . bottom of the pond should be al limestone to increase the pH to A good supply of freshwater is completely smooth and free of a minimum of 6.5, and preferably any potential obstructions to sein- 6.8. *Mississippi State University After filling the pond, fertilize the Stocking of juveniles sufficiently warm temperature for pond to provide an abundance of growth. natural food organisms for the Juvenile prawns must be gradual- prawns and to shade out unwant- ly acclimated to conditions in the Feeding ed aquatic weeds. Liquid fertiliz- grow-out pond to prevent temper- er, either a 10-34-0 or 13-38-0, or ature shock or other types of Juvenile prawns stocked into one of the highly water soluble stress. Water in which postlarvae grow-out ponds initially are able powders (12-49-6 or 10-52-0) give and juveniles are transported to obtain sufficient nutrition from excellent results. Apply 1/2 to 1 should be gradually replaced by natural pond organisms. At the gallon of liquid fertilizer or 4 to 6 the water in which they will be recommended stocking densities, pounds water soluble powder per stocked. This acclimation proce- begin feeding when the average surface acre to the pond at least dure should not be attempted weight of the prawn is 5.0g or 1 to 2 weeks before stocking juve- until the temperature difference greater. Commercially available nile prawns. If a phytoplankton between the transport and culture sinking channel catfish feed (28 to bloom has not developed within a water is less than 6 to 10°F. The 32 percent crude protein) is an week, either make a second appli- temperature of the pond water at effective and economical feed at cation of the fertilizer, or add stocking should be consistently at the recommended stocking densi- water from an adjacent pond that least 68°F (20°C) to avoid stress ties. The feeding rate is based has an adequate bloom to seed because of low temperatures. upon the mean weight of the pop- the bloom in the prawn pond. Do Juvenile prawns appear to be ulation (Table 1). A feeding sched- not apply liquid fertilizer directly more susceptible than adults to ule can be developed based upon into the water because it is denser low water temperatures. three factors: than water and will sink to the Juveniles, preferably derived from 1. A of 2.5; bottom; liquid fertilizer should be populations that have been size- 2. One percent mortality in the diluted with water 10:1 before graded, ranging in weight from population per week; and application. It can be sprayed 0.1 to 0.3g, should be stocked at from the bank or applied from a densities of 12,000 to 16,000 per 3. Mean individual weight deter- boat distributed in the propwash acre. The size grading results in mined from samples obtained of an outboard motor. The water more uniform growth and helps every 3 weeks. soluble powders can be applied to reduce the percentage of small- At the end of the grow-out sea- directly to the water surface, or er, non-marketable individuals at son, survival may range from 60 distributed with a boat or via cur- harvest. Lower stocking densities to 85 percent, if you have prac- rents created by a paddlewheel will yield larger prawns but lower ticed good water quality mainte- aerator. total harvested poundage. The nance. Yields typically range from If a water source other than well density selected should be deter- 600 to 1,200 pounds per acre. water is used, it is critically mined by the particular market Weights of prawns range from 35 important to prevent fish, particu- that is targeted. For example, if to 45g (13 to 10 per pound). These larly members of the sunfish fam- the market demands whole, live yields and average sizes, however, ily (e.g., , bluegills and green or fresh ice-packed prawn, stock- will be significantly influenced by sunfish) from getting into the ing at lower densities will result initial stocking density. pond when it is filled. Screening in larger, more marketable indi- or filtering the incoming water is viduals. The duration of the grow- Water quality management highly advisable. The effects of out period depends on the water Water quality is just as important predation on freshwater prawns temperature of the ponds, and the in raising freshwater prawns as it by these kinds of fish can be dev- time generally is 120 to 180 days is in raising catfish or any other astating. If there are fish in the in the southern U.S. Prawns could species of aquatic animal. Dis- pond, remove them before stock- be grown year-round if a water solved oxygen (DO) is particularly ing prawns, using 1 quart of 5 source is found that provides a percent liquid emulsifiable rotenone per acre-foot of water Table 1. Weight-dependent feeding rates for semi-intensive pond when water temperatures exceed grow-out of rosenbergii. 70oF. Rotenone is a restricted use pesticide, and either a commercial Mean wet weight (g) Daily feeding rate or private pesticide applicators (% of body weight)a license is required to purchase <5 0 and apply this material. Assistance in obtaining this 5 to 15 7 license or certification can be 15 to 25 5 obtained through your county >25 3 Extension office. *As-fed weight of /wet biomass of prawns x 100. important, and a good oxygen lethal. Chronically low levels of tively prevents oxygen depletions. monitoring program is necessary dissolved oxygen result in less Another reliable method to pre- to achieve maximum yields. You than anticipated yields at the end dict low DO levels is to plot the should routinely check and moni- of the growing season. Emergency level an hour after sunset and tor dissolved oxygen in the bot- aeration can be achieved by an approximately 2 hours later. Plot tom 1 foot of the pond which the aerator. The design and size of the these two readings on a piece of prawns occupy. Electronic oxygen aerator depend on the size and graph paper and connect them meters are best for this purpose shape of the culture pond, but a with a straight line (Figures 1 and but are rather expensive and good rule of thumb is to have 2). Oxygen consumption during require careful maintenance to available 1 HP of aerator per sur- the late evening and early morn- ensure good operating condition. face acre of pond. ing proceeds at a constant rate, The need for an electronic oxygen Prevention of thermal stratifica- caused by the respiration of the meter increases as the quantity of tion is important, since prawns animals and plants in the water. ponds to be managed increases. are bottom dwellers, and stratifi- By extending the line from these With only one or two small cation results in two potential two points over time you can ponds, a chemical oxygen test kit problems. First, since the bottom quickly determine if the dawn DO is sufficient. Chemical oxygen layer is cool, prawn growth can be concentration will decrease to the tests kits that perform 100 tests severely retarded. Secondly, these 3 ppm concentration that will are commercially available from bottom layers often become anox- stress or possibly kill the prawns. several manufacturers. ic, and stress or mortality of the This method indicates whether Use a sampler for collecting sam- prawns can result. If ponds do not emergency aeration is necessary ples from an appropriate water exceed the recommended depth, and when to provide it. Addi- depth for dissolved oxygen analy- and aeration is properly employ- tional information of pond aera- sis. These sampling devices are ed, thermal stratification is unlike- tion is available in SRAC Publi- commercially available or can be ly. cations # 370, Pond Aeration, and fashioned. It is important the dis- 371, Types and Uses of Aeration Oxygen depletions can be avoid- Equipment. solved oxygen concentration in ed. An increasingly popular the bottom 1 foot of water does method is to employ either full- Specific information on water not fall below 3 parts per million time or nightly aeration. Since quality requirements of freshwa- (ppm). Dissolved oxygen concen- standing crop biomass seldom ter prawns is limited. Although trations of 3 ppm are stressful, exceeds 1,000 lb/acre, this effec- freshwater prawns have been suc- and lower concentrations can be cessfully raised in soft water (5 to

Figure 1. Graphic method of predicting nighttime oxygen Figure 2. Graphic method of predicting nighttime oxygen depletions depletions in ponds. In this example it is predicted the oxygen in ponds. In this example it is predicted that no oxygen problem will concentration will drop to 2 ppm by 2:40 a.m., indicating develop in the pond during the night. emergency aeration should be started by 3:30 a.m. 7 ppm total hardness) in South Another way to manage to avoid Selective harvest of large prawns Carolina, a softening of the shell any anticipated problems of high during a period of 4 to 6 weeks was noticed. Hard water, 300-plus pH is to reduce the quantity of before final harvest is recom- ppm, has been implicated in algae in the pond by periodic mended to increase total produc- reduced growth and lime encrus- flushing (removing) the top 12 tion in the pond. Selective har- tations on freshwater prawns. inches of surface water. Alterna- vesting usually is performed with Therefore, use of water with a tively, organic matter, such as corn a 1- to 2-inch bar-mesh seine, hardness of 300-plus ppm is not grain or rice bran, can be distrib- allowing those that pass through recommended. uted over the surface area of the the seine to remain in the pond pond. This procedure must be and to continue to grow, while the Nitrogen compounds accompanied by careful monitor- larger prawns are removed. ing of oxygen levels, which may Selective harvest may also be Nitrites at concentrations of 1.8 dramatically decrease due to accomplished with properly ppm have caused problems in decay processes. designed traps. Prawns can be hatcheries but there is no defini- trapped using an array of tradi- tive information as to the toxicity Diseases tionally designed crawfish traps. of nitrite to prawns in pond situa- Selective harvest can help to tions. High nitrite concentrations Diseases so far do not appear to extend the duration of the avail- in ponds would not be expected be a significant problem in the ability of the fresh or live prawn given the anticipated biomass of production of freshwater prawns, product to the market. However, prawns at harvest. High levels of but, as densities are increased to there is a lack of research to show un-ionized ammonia, above 0.1 improve production, disease prob- whether selective harvesting or a ppm, in fish ponds can be detri- lems are bound to become more complete bulk harvest is the most mental. Concentrations of un-ion- prevalent. One disease you may economical approach. ized ammonia as low as 0.26 ppm encounter is “blackspot” or “shell at a pH of 6.83 have been reported disease,” which is caused by bac- Regardless of the harvest method to kill 50 percent of the prawns in teria that break down the outer employed, some prawns will a population in 144 hours. skeleton. Usually it follows physi- remain in the bottom of the pond Therefore, you must make every cal damage and can be avoided by and will have to be manually effort to prevent concentrations of careful handling. At other times, picked up. Rapid draining or care- 0.1 or higher ppm un-ionized algae or insect eggs may be pre- ful seining can minimize this ammonia. For more information sent on the shell. This condition is residual crop left in the pond. on ammonia and nitrites in fish not a disease, but rather an indica- Prawns should be quickly chilled ponds, request SRAC Publications tion of slow growth, and is elimi- after harvest to preserve integrity # 462, Nitrite in Fish Ponds, and nated when the prawn molts. of the muscle tissue, thus main- #463, Ammonia in Fish Ponds. taining a firm, high quality texture Harvesting to the product. The product may Acceptable pH ranges be marketed fresh on ice, or may At the end of the grow-out sea- be either processed and frozen or son, prawns may be seine- or A high pH can cause mortality frozen whole for storage and ship- drain-harvested. For seining, through direct pH toxicity, and ment. indirectly because a higher per- depth (or water volume) should centage of the total ammonia in be decreased by one-half before the water exists in the toxic, un- seining. Alternatively, ponds Polyculture and ionized form. Although freshwa- could be drained into an interior intercropping large rectangular borrow pit ter prawns have been raised in Culture of freshwater prawns in (ditch) where prawns are concen- ponds with a pH range of 6.0 to combination with fingerling cat- trated before seining. You can 10.5 with no apparent short-term fish has been successfully demon- effectively drain harvest only if adverse effects, it is best to avoid strated under small-scale, experi- ponds have a smooth bottom and a pH below 6.5 or above 9.5, if mental conditions, and appears a slope that will insure rapid and possible. Constantly high pH possible under commercial condi- complete draining. During the stresses the prawns and reduces tions. Before introduction of cat- complete drain-down harvest pro- growth rates. High pH values fish fry, stock juvenile prawns at a cedure, prawns generally are col- usually occur in waters with total rate of 3,000 to 5,000 per acre. lected on the outside of the pond alkalinity of 50 or less ppm and Stock catfish fry at a density to levee as they travel through the when a dense algae bloom is pre- insure that they will pass through drain pipe into a collecting device. sent. Before stocking, liming a 1-inch-mesh seine used to har- To avoid stress and possible mor- ponds that are built in acid soils vest the prawns at the end of the tality, provide sufficient aeration can help minimize severe pH fluc- growing season. Although poly- to the water in the collection tuations. culture of prawns and a mixed device. population of channel catfish has June before stocking of new adult Transport under these conditions been successfully demonstrated, crawfish. Prawns are small requires good aeration. Distribu- logistical problems arising from enough to pass through the mesh tion of prawns on “shelves” efficient separation of the two of the seine used to harvest craw- stacked vertically within the crops is inherent in this manage- fish during the May-June overlap water column assists in avoiding ment practice. Moreover, when period. Other intercropping sce- mortality due to crowding and harvest of prawns is imminent narios involving such species as localized poor water quality. Use due to cold water temperatures, bait minnows, and other of holding water with a compara- catfish may not be a harvestable fish species may be possible, but tively cool temperature (68 to crop due to an “off flavor” charac- to date no research has been con- 72°F) minimized incidence of teristic. Polyculture of channel cat- ducted in the Southeast. water quality problems and injury fish and freshwater prawns may by reducing the activity level of be best achieved through cage cul- Processing and marketing the prawns. ture of the fish. Production levels and harvesting Economic feasibility Recently, a scheme for intercrop- practices should match marketing ping of freshwater prawns and strategies. Without this approach, Based on an average feed cost of red swamp crawfish was devel- financial loss due to lack of ade- $250 to $300 per ton, a seedstock oped and evaluated (Figure 3). quate storage (holding) facilities cost of $65 per 1,000 juveniles, a Intercropping is the culture of two or price change is inevitable. 2.5 to 1 feed conversion, expected species that are stocked at differ- Marketing studies strongly sug- mean yields of 1,000 pounds per ent times of the year with little, if gest that a “heads off” product acre, and a pond bank selling any, overlap of their growth and should be avoided and that a spe- price of $4.25 per pound, the harvest seasons. Intercropping cific market niche for whole fresh- expected return can be as high as provides for a number of benefits water prawns needs to be identi- $2,000 to $2,500 per acre. Revenue that include: fied and carefully developed. and ultimate profitability depend 1. Minimizing competition for To establish year-round distribu- on the type of market that is used. resources; tion of this seasonal product, This estimated return does not 2. Avoiding potential problems of freezing, preferably individually include labor costs or other vari- species separation during or quick frozen (IQF), is an attractive able costs that differ greatly from after harvest; and form of processing, and recent operation to operation. Some thor- ough economic evaluations that 3. Spreading fixed costs of a pro- research has demonstrated its effi- cacy and potential. Block frozen is incorporate annual ownership duction unit (pond) throughout and operating costs under differ- the calendar year. an alternative method of process- ing for long-term distribution. ent scenarios for a synthesized Adult mature crawfish are Recent research at the Mississippi firm of 43 acres, having 10.25 stocked at a rate of 3,600 per acre Agriculture and Forestry acres of water surface in produc- in late June or early July. Juvenile Experiment Station suggests that tion, are provided in Mississippi prawns are stocked at a density of adult freshwater prawns can be Agriculture and Forestry 16,000 per acre in late May and successfully live hauled for at Experiment Station Bulletin 985, harvested from August through least 24 hours, at a density of 0.5 available from the Department of early October. In late February, pound per gallon, with little mor- Agricultural Economics, seine harvest of the crawfish tality and no observed effect on Mississippi State University. begins and continues through late exterior quality of the product.

Figure 3. A 24-month stocking and harvest scheme for intercropping freshwater prawns and crawfish. All years follow- ing year 2 will be the same as year 2. The work reported in this publication was supported in part by the Southern Regional Center through Grant No. 89-38500-4516 from the United States Department of Agriculture.