SRAC Publication No. 484

July 2006 VI Revision PR

Pond Production of the Freshwater Prawn in Temperate Climates

Louis R. D’Abramo1, James H. Tidwell2, Mack Fondren3 and Cortney L. Ohs4

Pond production of freshwater Site selection Pond construction prawns, Macrobrachium rosenbergii, in temperate climates involves The proper design and construction Properly designed and construct- stocking nursed, juvenile prawns of ponds for freshwater prawns are ed ponds can have a tremendous 1 extremely important. When select- effect on harvest efficiency. into ponds, followed by 3 ⁄2 to 6 months of growout until they are ing a site, avoid areas that are Harvesting freshwater prawns is ready for harvest. The exact prone to flooding. The location extremely labor intensive if ponds growout time depends on the tem- must be suitable for pond construc- are poorly designed or construct- perature range within the growing tion and have an adequate water ed. The first decision should be season. Successful pond produc- supply. The soil should have good the placement of the harvest basin tion of prawns begins with site water retention qualities. Both the (internal versus external) and the selection, pond construction, and soil and water must be free of drainage from that basin. The planning for a water source. The chemical residues such as pestici- depth of the harvest basin and the production cycle requires pre- dal organic compounds that could drainage leaving the basin will stocking preparation, stocking, be harmful or lethal to prawns. determine pond configuration. feeding, and managing water quali- Have the soil tested for pesticides A prawn pond is about 3 to 3.5 ty until harvest. A recent examina- known to have been used on the feet deep at the shallow end and tion of the economics of pond pro- site. County Extension offices have slopes to 4.5 to 5.5 feet at the duction of freshwater prawns in instructions and containers for soil deep end. A shallow-end water temperate climates has been pub- samples. To prepare samples, col- depth of 3.5 feet is recommended lished (Dasgupta, 2005). Other lect small soil samples from several to discourage the growth of nui- aspects of prawn culture in ponds, (six to eight) locations in the area sance weeds (aquatic rooted as well as hatchery and nursery where you intend to locate a pond. plants and filamentous algae) dur- culture and general biology, can be Samples from the lowest lying ing the production season and found in Tidwell et al. (2005), New areas must be included because keep the water from cooling too and Valenti (2000), D’Abramo and they generally have the highest lev- rapidly when cooler air tempera- Brunson (1996), and Daniels et al. els of contaminants if any are pre- tures arrive at the end of the (1992). sent. Thoroughly mix the samples growing season. and allow the soil to dry. Then fill the container with a sample of the The inside slopes of levees gener- dried soil for analysis. Most states ally range from 2:1 to 3:1. Slope may vary somewhat with pond 1 operate laboratories that will Professor, Department of Wildlife and size and soil type, but a slope of Fisheries, Mississippi State University. process the samples and send a 2 Professor and Chair, Division of prepared report for a small fee. It 2:1 is recommended for highly Aquaculture, Kentucky State University. is important to inform the laborato- effective control of unwanted 3 Facilities Coordinator, Department of ry about your plans to use this land aquatic vegetation. Levee tops Wildlife and Fisheries, Mississippi State for a pond site so they can conduct that are 20 feet wide should be University. the appropriate tests (generally pH adequate, though some farmers 4 Assistant Professor, Department of and particle size analysis) and offer prefer a wider main levee (work- Fisheries and Aquatic Sciences, the proper recommendations. ing levee), usually located at the University of Florida. deep end of the pond. This wider working levee gives equipment prawns that can be sold fresh or draining, a large number of and laborers better access to the on ice, or processed and frozen prawns may be left stranded in harvest basin. Erosion from wind without suffering holding losses, muddy depressions and have to and waves generally has a modest and the potential for losing unhar- be removed manually. If this is effect on prawn ponds, which are vested prawns when temperature not done quickly, their condition usually smaller than 3 acres. falls at the end of the growing sea- may become unacceptable for There should be about 1 foot of son. In a properly designed and processing. extra soil height (levee freeboard) constructed pond, about 75 per- Harvest basins can be external or above the operating water level of cent of the prawns may leave the internal, but should be designed the pond to add structural stabili- pond as the last 20 percent of the so that all pond water drains ty and capture rainwater. water exits (if harvesting to an rapidly into them. Bottom contours and drain harvest external harvest basin). The abili- structures are the most important ty to manually remove all prawns External harvest basin aspects of freshwater prawn pond (including any stranded on the pond bottom) and process them The external (outside the levee) design because they affect efficien- harvest basin design consists of a cy of harvest. The pond bottom on site depends on the availability of a sufficient labor force and/or fan-shaped (wide V from over- should have no obstructions or head), deepened area (6 inches deep depressions to interfere with ice-packing facility. Ponds smaller than an acre may yield more per deep, 20 to 30 feet wide, and the goal of concentrating all approximately 30 feet from the prawns into one area during drain acre than larger ponds if the shape of larger ponds reduces the drain pipe) within the pond where harvest. Slopes of 7 to 9 inches per prawns are initially concentrated. 100 feet of pond length and about ratio of perimeter to total surface area. Under similar management This area is called an internal con- 7 inches per 100 feet from the side centration basin. The fan is levees to the center of the pond are practices, higher ratios are believed to promote higher yields. tapered and slopes to the focal recommended. These measure- point (V-shaped end), which is ments are taken from the toe (bot- If a formulated feed is to be used, located at the opening of the drain tom of the slope) of the inner lev- the pond shape should allow feed harvest pipe (Fig. 1). Shallow ees. During harvest, pond contours to be distributed over the entire trenching within the internal con- should direct the movement of the surface of the pond because fresh- centration basin may help direct prawns as they follow the water water prawns are territorial. the flow of prawns farther and flow into a wide, shallow, V-shaped Feeding with the wind increases concentrate them as they follow channel along the length of the the range of feeding equipment. the water flow to the drain har- pond. The channel flow will then The topography may allow for sit- vest pipe, and then to the harvest be directed toward either an inter- ing a pond to take advantage of basin located outside the pond nal concentration basin or an inter- prevailing winds. If fertilization is levee. Prawns that do not exit will nal harvest basin. An external har- the feeding strategy, distribution remain in the internal harvest vest basin is combined with an across the entire pond surface is basin. The bottom of the drain internal concentration basin, probably not critical. harvest pipe(s) should be about 6 whereas the internal harvest basin inches below the lowest point in design is a singular feature. Design for harvest the pond; this is referred to as “6 Harvesting by seine is not recom- inches below the low.” The pipe Pond size and shape mended. The process is labor should extend slightly past the toe Prawn pond sizes will be site-spe- intensive and may damage prawns of the inner levee and through the cific as determined by land topog- if they become entangled and are outer levee to a point suitable for raphy, desired pond shape, and dragged through the mud of the emptying water into the external the associated feeding, harvesting pond bottom. Prawns naturally harvest basin. The pipe(s) must and processing capacities. Pond follow a flow of water, so drain have an adequate slope to move shape and size should fit manage- harvest is a passive, yet efficient, the water and prawns (Fig. 2). ment practices and capabilities. method of collecting prawns. If The purpose of the external har- However, size typically ranges the pond is poorly designed for vest basin is to collect the prawns from 1 to 5 acres and the pre- ferred shape is rectangular. A plan that allies design and con- struction decisions with harvest intentions (product form and pro- cessing capabilities) is very impor- tant. Chances for success greatly increase when pond design and logistics (harvest plan) are compat- ible. Total pond acreage and rate of harvest should be determined Figure 1. Cross-sectional side view of a pond designed for drain harvest to an by the number of pounds of external harvest basin. and hold them under good water while holding all prawns. Livecars mesh size to prevent prawns from quality conditions until time to staked out in drainage ditches and escaping the pond. Being able to transport them for live holding or expanded metal boxes with mesh exchange screens of increasing processing. Therefore, the water have been used to hold prawns. A mesh size throughout the produc- will need to be well aerated to concrete basin equipped with tion period also can be beneficial. maintain adequate levels of dis- mesh drainage areas is a perma- Several types of pipe are available solved oxygen. Otherwise, the nent and highly effective option. and cost is always an important prawns will be stressed. The The diameter of the drainage pipes factor. Underground, smooth- external harvest basin must allow should be based on the acreage of walled pip (piping used in the irri- the water to drain from the pond the pond; all water should drain gation industry) may be a more from the pond within 6 to 8 hours. economical choice than schedule It is important to be able to drain 40 PVC. Pipe can be purchased at the entire pond rapidly and to vary businesses specializing in irrigation the rate of flow exiting the pond. equipment. Rate of flow through Drain harvests of properly the harvest drainpipe is often con- designed 1- to 3-acre ponds have trolled by a piece of plywood or demonstrated that a single 12- to some other flat, sturdy surface and 16-inch-diameter pipe or two 8- to an alfalfa valve (Figs. 3a and 3b). 10-inch-diameter pipes will drain Plywood or another suitable mate- ponds within the desired time. If rial also is used as a primitive gate grass carp have been stocked to or guillotine valve on the inflow control aquatic weeds, workers end (pond side) of the drainpipe. It must be careful to keep the carp should be put in place before out of drain pipes less than 12 stocking the pond. It serves as a inches in diameter. Carp tend to safety valve if problems in the lodge themselves sideways in the operation of the alfalfa valve arise. pipes, preventing prawns from Check the placement of this gate exiting. Removing the carp can be before opening the alfalfa valve. a laborious, time-consuming task. The alfalfa valve is used to stop If standpipes are used, a second the flow of water leaving the pond smaller pipe that extends through and should be located on the out- the levee to control water level is side of the pond at the external recommended. This design is gen- harvest basin. Be sure the valve erally more cost-effective than the and pipe are compatible and that fittings, pipe and screen required the alfalfa valve has an arch, a to make the drain harvest pipe removable central yolk within the also serve for pond water over- valve. After this arch (yolk) is flow. Regardless of its size and removed from the valve, water Figure 2. Overhead view of a pond design, the standpipe should be passes without obstruction designed with an external harvest fitted with screening of adequate through the harvest pipe and into basin. a b

Figure 3. Cross-sectional side (a) and overhead (b) view of an alfalfa valve with a removable arch. the harvest basin. An alternative so there is no need for another area to a three-dimensional area. to a standpipe for the control of standpipe. The placement of the In ponds without natural (perime- water level within a pond is an in- drain pipe within the internal har- ter vegetation) or artificial sub- line water control structure. Slats vest basin should be determined by strate, the territorial prawns are within the drain structure are external drainage features or cost. confined to the benthic (bottom) either added or removed to main- The internal harvest basin must be area of a pond. Therefore, as the tain the desired water level. drained as completely as possible to growing season progresses, the Clean pond water must flow ensure complete harvest. total weight (biomass) of the through the catch basin. As the If an external pond drain valve is prawns in a pond increases and harvest progresses, prawns should fitted to the drainage structure and the corresponding amount of bot- be removed from the catch basin all prawns are to be harvested from tom area available per unit of periodically. To keep prawns clean, the basin within the pond, then an body weight decreases. As a water may need to be added from alfalfa valve with a removable arch result, growth rates decrease and a well or a neighboring pond to is not necessary. Various types of mean individual weights at har- flow through the catch basin and valves can be used, including an vest are lower in ponds with com- external harvest basin of a harvest- alfalfa valve with a fixed arch. paratively higher densities of ed pond. Water leaving the harvest prawns. This response is called basin must have adequate drainage Substrate density-dependent growth. Adding substrate removes or so it will not back up into the har- Adding substrate to a prawn pond delays problems associated with vest basin and cause it to overflow. changes it from a two-dimensional Structures such as rip-rap should density-dependent growth be placed along the drainage ditch because there is more area for that is receiving the flow of water prawns within the pond. As a to reduce erosion, because a large result, production increases. The volume of water flows when har- preferred substrate is the orange vest begins. polyethylene safety fencing that is often installed around construc- Internal harvest basin tion sites. It is comparatively Having only an internal harvest inexpensive and durable. basin requires few changes in Alternative materials should be overall pond design. Levee slopes equally effective, such as large- and tops, grade, and pond bottom mesh, less expensive monofila- contours are similar except for the ment netting. incorporation of a rectangular Studies suggest that using a mesh internal harvest basin. The internal substrate equivalent to 25 percent harvest basin is located at the deep of the bottom surface area end of the pond and is 1 to 2 feet increases harvest yield by 15 to deeper than the rest of the pond 20 percent. The actual amount of bottom. It is much larger and mesh substrate required is calcu- deeper than the fan-shaped inter- lated by including the area nal concentration basin used with (excluding mesh) of both sides of an external harvest basin. An inter- the substrate. The size of the nal harvest basin stretches across mesh may not be as important as most of the width and about 15 the overall amount of substrate feet along the length of the pond used. Generally, 11,000 to 15,000 bottom. Harvest is conducted by square feet of substrate (calcula- lowering the pond water level to tion based on one side) are the level of the internal harvest Figure 4. Overhead view of a pond required per water surface acre, basin, where prawns are concen- designed with an internal harvest assuming the average depth of the basin. trated and then removed with a small seine or, if necessary, manu- ally. It is absolutely essential to be able to aerate the water in the internal harvest basin (using a ver- tical lift or similar type of aerator). The slope within the basin must be directed to the drainpipe (Figs. 4 and 5). A single 12-inch pipe screened at the top, with a swivel type elbow at the bottom, should be sufficient. This pipe serves as both a drain pipe and a standpipe, Figure 5. Cross-sectional view of a pond designed with an internal harvest basin. to stimulate an algal bloom and a bacteria-based system within the water column. This will keep sun- light from reaching the bottom of the pond and prevent the growth of aquatic weeds such as Chara sp. and Najas sp. (Brunson et al., 1994). Figure 6. Cross-sectional view of a pond with focus on the internal harvest A liquid inorganic fertilizer— basin. either a 10-34-0 or a 13-38-0— gives the best results. It should be added to the pond water at a rate pond is approximately 3.5 feet. To every 1.73 mg of gypsum added 1 of 1.9 L ( ⁄2 gallon) per surface get maximum use of the substrate, per liter of water. Alkalinity acre to stimulate blooms of it should be suspended vertically should range from at least 50 microscopic algae. Inorganic fertil- within the water column and posi- mg/L to 150 mg/L. Agricultural ization is most effective when tioned about 6 inches above the lime can be used to increase both pond water temperatures exceed bottom and below the surface of alkalinity and hardness. The pH of 65 degrees F. If water has low the water. It may not be practical the water should be between 7.0 hardness, adding lime will to install substrate in ponds larger and 8.5. A total alkalinity of 100 increase the effectiveness of the than 2 to 3 acres. This is the size of to 150 mg/L will stabilize pH by inorganic fertilizer. If possible, most commercial ponds used for buffering from the carbonate frac- this procedure should be comple- the culture of Macrobrachium. tion of the limestone (Wurts and mented by adding water from Durborow, 1992). Studies have demonstrated that ponds with already established using substrate increases yield Pond preparation and populations of desirable phyto- regardless of stocking density. The plankton (a process called seed- cost and durability of the material stocking ing). If either rooted plants or used must be weighed against the Prawns should not be stocked in floating filamentous algae (“moss”) increase in production that is real- ponds containing fish. Fish are plants appear, no additional inor- ized. potential predators and/or com- ganic fertilizer should be applied because it will encourage the Water sources and quality petitors for natural food resources and feed. Fish must be eradicated growth of these undesirable aquat- Well water is recommended for before stocking prawns, either by ic plants. Dense nuisance plants freshwater prawn production. draining the entire pond or by can interfere with applying feed Water sources that may have been applying 3 pints (1.41 L) of 5% and fertilizers and with harvest. contaminated by pesticide runoff emulsifiable rotenone (Fintrol®), a Organic fertilizers that can be should be tested to be sure they piscicide, per acre-foot of water. used in a prawn pond include dis- are suitable for raising prawns. If This product can not be applied tillers dried grains and solubles surface water is used to fill ponds, without a certified pesticide appli- (DDGS), cottonseed meal, alfalfa be careful to keep fish from enter- cator’s license or direct supervi- meal, soybean meal, sinking cat- ing. Some species of fish will eat sion by someone who has been fish feed or combinations of these small prawns and the feed or fertil- licensed. Rotenone is potentially materials. Make the first applica- izer that is added to ponds as a toxic to prawns. The rate at which tion, at a rate of 200 pounds per source of nutrition for the prawns. it breaks down after application is acre, within a day after filling the Besides chemical pollution, the influenced by temperature, light, pond. Thereafter, apply the cho- principal water quality concerns in levels of dissolved oxygen, and sen fertilizer at a rate of 15 to 20 freshwater prawn production are alkalinity. Generally, prawns can pounds per acre every other day hardness, alkalinity and pH. Water be stocked 2 to 3 weeks after until stocking to enhance produc- hardness should range between 50 application. To ensure that condi- tion of natural food organisms for and 200 mg/L. Lower levels reduce tions are safe, place four or five the prawns. Once the prawns the hardness of the calcium-based juvenile prawns into two or more have been stocked, follow the rec- shell of prawns; higher levels may small cages suspended from floats ommendations for organic fertil- reduce growth and produce lime and let them drift within the ization (see the Feeds and Feeding water column at different loca- section). The choice of an organic (CaCO3) encrustations on the shells. To increase the hardness of the tions in the pond. If the prawns fertilizer should be based on cost water, calcium must be added; agri- survive for 48 hours, any chemical and availability. residue is probably gone. cultural gypsum (CaSO4 2H2O) is If pH values fail to stabilize natu- recommended. The purity of this Ponds should be filled with water rally in ponds before stocking, compound varies from 70 to 98 per- and fertilized about 2 to 3 weeks sodium bicarbonate should be cent. Assuming the product used is before they will be stocked. added. However, this compound 100 percent pure, total hardness Ponds should be fertilized with does not change pH significantly can be increased by 1 mg/L for inorganic and organic fertilizers and its effect is not long lasting (see the Water Quality and ual growth is influenced by the comparable to those using sinking Management section). total amount of prawn biomass in catfish feed. Therefore, using these Ponds should be stocked as soon as the pond. Therefore, choice of a less expensive fertilizers, either it is certain that water temperatures stocking density will probably be alone or in combination, may in the early morning will consis- determined by the market and reduce variable costs considerably. tently remain above 68 degrees F. marketing strategies. Recommended feeding rates are Stocking may occur from late April estimates based upon two factors— though mid-June, depending on the Feeds and feeding rates water temperature and prawn bio- region. Because of the limited As in other types of animal agri- mass (determined by estimates of growing season, only juveniles culture, successful prawn culture individual weight, density and sur- should be stocked, regardless of is based upon realizing high-value vival). The daily rate of fertilizer stocking density. The mean stock- outputs (prawns) from low-cost application increases as the length ing weight should be 0.25 to 0.40 g inputs (fertilizer and feed). The of the growing season increases, to realize the best return for the objective is to achieve maximum but generally should not exceed 70 purchase cost of juveniles. In growth by providing a continuous lb/A. The total amount of post- regions where the growing season source of nutrition as inexpensive- stocking fertilizer/feed needed, is shortest, the stocking weight ly as possible without overfeeding. expressed as a ratio relative to the should be at the high end of the Overfeeding not only reduces total anticipated production, is range. The range in juvenile stock- potential revenue but also can approximately 3.5 to 4.0. A recom- ing weight is usually the result of lead to poor water quality that can mended rate of application for a postlarvae having been held in the impair growth. 20-week growout period, expressed nursery phase of culture for differ- as a percentage of total Organic fertilizer enhances the nat- ent lengths of time (generally 40 to fertilizer/feed, is presented in Table ural productivity of ponds so that 60 days). Smaller juveniles are less 1. With higher initial stocking den- sufficient natural food organisms expensive, but just a small increase sities, production is anticipated to (insect larvae, worms, etc.) are avail- in stocking weight, from 0.14 g to increase and the total amount of able for prawns. Organic fertiliza- 0.25 g, can result in a 40 percent feed and corresponding daily rates tion continues throughout the grow- increase in production for a 120- to of application per acre will ing season, provided that the 130-day growout period. Purchasing increase based upon these percent- demand for food by the prawns juvenile prawns with a mean ages. Applying this level of organic does not exceed the rate at which weight of more than 0.40 g is not fertilizer will probably be sufficient natural food organisms are being an efficient alternative because for stocking densities up to approx- produced. Sinking catfish feed has transporting them requires larger imately 24,000/A. At higher stock- traditionally been the recommend- volumes of water, an expense that ing densities, this amount of fertil- ed feed/fertilizer, but other pelleted is aggravated if they must be trans- izer probably will not produce the forms of agricultural feeds or feed- ported a considerable distance. In quantity of natural food required stuffs, such as corn gluten pellets, addition, purchasing these more for maximum prawn growth rate wheat midds, or range cubes, also expensive juveniles will substantial- during the final 3 to 4 weeks of have been used. The protein con- ly increase the variable costs of an growout. At this last stage of tent of these products ranges from enterprise, usually without enough growth, prawns may need to be fed 17 to 20 percent (as is) or 20 to additional revenue to compensate a water-stable, nutritionally com- 20.3 percent on a dry weight basis. for it. plete prawn diet as a supplement. The survival, mean individual har- However, the cost-effectiveness of Before stocking, make sure the vest weight, and harvest yield using a supplement is questionable. temperature of the pond water is achieved with these fertilizers in Formulated feeds may be cost- similar to that of the transport production experiments have been water. If the difference is greater effective only when yields are than 5 degrees F, the prawns expected to exceed 1,500 lb/A. should be gradually acclimated to the temperature of the pond water. Table 1. Recommended percent- Polyculture This can be accomplished by grad- ages of total organic fertilizer/ The concept of prawn and fish ually mixing the pond water (at feeds for the pond culture of polyculture is based upon the least 50 percent replacement) with Macrobrachium rosenbergii dur- belief that the amount of biomass the prawn holding water, allowing ing specific time intervals of a 20- in prawn ponds that have been about 5 minutes for each degree of week maximum growout period. stocked at the lower end of the temperature increase. range of density can be increased Weeks Percentage of total Stocking rates that will provide without any detrimental effect. marketable prawns after a 4- to 5- 1 to 6 16.0 The ecological balance (chemical and biological) in a pond can be month growth season generally 7 to 11 27.8 range from 8,000 to 28,000 per better realized through the culture acre. Mean individual weight at 12 to 16 32.6 of two species. A number of fish species have been cultured in the harvest is inversely proportional to 17 to 20 23.6 stocking density because individ- same pond with prawns, including channel catfish, yellow perch and Water quality requirements remain within the range of 7.0 to tilapia. The best application of this and management 9.0. Prawns grow best at a pH of 7 polyculture management strategy to 8.5, but will still grow and sur- is to confine the fish in cages Other than the quality and quanti- vive at a pH as low as 6.5 and as floating in the prawn ponds. This ty of food consumed and water high as 9.5. A pH higher than 9.0 is design prevents fish from consum- temperature, dissolved oxygen and undesirable for stocking and any- ing prawns, aids in managing pH are the principal water quality thing higher usually is lethal to water quality, and facilitates the variables that influence prawn juvenile prawns (see the Pond harvest of the two species. To be growth and survival. These factors Preparation and Stocking section). suitable for polyculture, a fish must be monitored and main- Problems with high pH generally species must be a warm-water tained at satisfactory levels. occur in the late afternoon on species, adaptable to cage culture, sunny days during the early part of and able to reach marketable size Dissolved oxygen the production period, when inor- within 4 to 5 months. Based on Oxygen is the variable that can be ganic fertilization is used to pro- these criteria, the best candidate managed most effectively to mote fast-growing blooms of micro- appears to be Tilapia sp. improve annual yields. There scopic algae. Water of low alkalini- In experimental ponds, tilapia have must be some way to aerate ponds, ty (0.5 to 50 mg/L) is more prone to been stocked in cages at a density even when the stocking density undesirably high pH because its of 1.5 to 3 fish per cubic foot of and fertilization rate are low. capacity to buffer against high pH cage volume, up to a total of 1,000 Although prawns can survive when is reduced (Wurts and Durborow, to 2,000 fish per acre. Tilapia dissolved oxygen is below 2 ppm, 1992). Total alkalinity should be 50 weighing 100 g have been stocked at least 3 ppm should be main- to 150 mg/L (ppm), and can be in experimental ponds. Their mean tained to avoid stress and achieve increased to desired levels by weight at harvest has ranged from the highest growth rates. When applying agricultural lime (CaCO3). 470 to 500 g. In commercial cul- levels fall below or are anticipated Juvenile prawns appear to be more ture, the stocking size has ranged to fall below this concentration, susceptible to the harm of high pH from 50 to 400 g, depending on the pond water should be aerated by values. High afternoon pH general- size demand of the market the pro- an electric, in-pond aerator (1 hp ly ceases to become a problem as ducer desires to serve. The cages per water surface acre) and/or a organic matter begins to accumu- are located in the deepest areas of tractor-driven, paddlewheel aera- late and is routinely introduced the pond, so that at least 2 feet of tor. When water temperatures and into the pond. As the organic mat- clearance can be maintained feeding rates increase, dissolved ter decomposes, carbon dioxide is between the bottom of the cage oxygen should be monitored and produced and it usually keeps the and the pond bottom. Cages should recorded more often (at least early pH below 9.0. If pH begins to rise be located to benefit from water morning, late afternoon and late toward an undesirable value during circulation produced by an aerator evening). Levels of dissolved oxy- the early period of production, in the pond. Convenient access to gen are generally lowest just before organic matter should be added at the cages must be planned so that sunrise. An alternative is to aerate a rate of 15 lb/A, in addition to fish can be fed daily. A floating prawn ponds for 12 to 14 hours what has been recommended (see 32% protein catfish diet is ade- (2000 h to 0800 -1000 h) each day, the Feeds and Feeding Practices quate and tilapia should be fed as but this may still be insufficient to section), for about 7 days. To avoid much as they will actively con- prevent low levels of dissolved oxy- pH increasing to lethal levels, a sume (to satiation) in 10 to 20 min- gen so ponds still must be moni- rapid reduction in pH can be utes. In polyculture, prawns bene- tored. Aerators should be located at achieved through the addition of fit from two additional sources of the deep end and near the drain DePhos-A®, buffered alum (sodium organic material, undigested food basin area to minimize the accu- bicarbonate and aluminum potassi- and any uneaten food that sinks to mulation of sediment there. If aera- um sulfate AlK(SO4)2 at a ratio of the bottom of the pond. It has been tors are located in the shallow end, 1:1 in powder form). For every 0.5 suggested that the rate of applica- a shallow depression will form reduction of pH desired, the added tion of fertilizer/feed for the below them and cause prawns to alum must be dissolved in the prawns could possibly be reduced be stranded in a large pool during water to produce a concentration of by about 25 percent without any a drain harvest. If pond depth 10 ppm (approximately 42 lb/A corresponding need to reduce the exceeds what is recommended (see each of both alum and sodium prawn stocking rate. Polyculture the Pond Construction section), bicarbonate). pH should be moni- can be combined with added sub- then stratification can occur, caus- tored before and within a few strate in intensively managed ing levels of dissolved oxygen in hours after introduction to deter- ponds and may have its best appli- the bottom water layer to be low mine whether more might need to cation in these same smaller or even reach lethal levels. be gradually added to achieve the ponds. These systems require more desired pH. Initial additions should frequent monitoring of water quali- pH not exceed a concentration that will ty and possibly more aeration. produce a one unit decrease in pH. To avoid stress and possible mor- Additional amounts may be needed tality, the pH of the water should if pH begins to increase again ponds designed for drain down D’Abramo, L.R. and M.W. toward potentially lethal levels into harvest basins located either Brunson. 1996. Production of (> 9.5). within the pond or on the outside freshwater prawns in ponds. An alternative way to prevent of the pond levee (see Harvest Southern Regional lethally high pH from occurring, Methods and Basin Design sec- Aquaculture Center (SRAC) particularly from infestations of tion). The harvest basins must be Publication No. 484. filamentous algae, is to apply an well aerated as the prawns are Daniels, W.H., L.R. D'Abramo and algal herbicide such as Hyrothol®. concentrated and removed. Where L. de Parseval. 1992. Design Tests have shown that Hyrothol® the growout phase is more than and management of a recircu- has no effect on prawn survival 160 days, it may be helpful to lating "clearwater" system for when the level of application for seine out the largest prawns 25 to larval culture of the freshwa- treatment does not exceed 0.2 40 days before complete harvest. ter prawn Macrobra-chium ppm. Another possibly effective This often causes a sufficient com- rosenbergii de Man, 1879. herbicide is Green Clean® (sodium pensatory growth response in the Journal of Shellfish Research carbonate peroxyhydrate), but remaining population to make the 11:65-74. practice cost-effective. information about whether it is Dasgupta, S. Economics of fresh- lethal to prawns under the recom- Currently, yield from a single- water prawn farming in the mended levels of application is batch harvest (no selective har- United States. 2005. Southern lacking. The application of a her- vest) of most commercial enter- Regional Aquaculture Center bicide must be accompanied by prises in the U.S. ranges from 600 (SRAC) Publication No. 4830. frequent monitoring of dissolved to 1,800 lb/A. Yield is influenced oxygen, as the decomposition of by a combination of factors that New, M.B. and W.C. Valenti (edi- dead algae consumes oxygen. include stocking density, stocking tors) 2000. Freshwater Prawn Although these herbicides are size, duration of growout, shape of Culture: The farming of short-lived (rapidly decomposed), pond, presence of substrate, and Macrobrachium rosenbergii they should be used as a last selective harvest. Stocking density Blackwell Science Ltd., resort because their possible is inversely related to growth Oxford, 443 pps. effect on prawn growth has not rates, but directly related to over- Tidwell, J.H., L.R. D’Abramo, S.D. been determined. Copper sulfate all production at equivalent levels Coyle and D. Yasharian. should never be used as an algi- of survival. The presence of plants 2005. Overview of recent cide in prawn production ponds around the perimeter of the pond research and development in because extremely low levels of is believed to improve yield and is temperate culture of the fresh- copper are toxic to prawns. probably associated with the bene- water prawn (Macrobrachium ficial effects of substrate. Water rosenbergii De Man) in the Harvest circulation may also improve south central United States. yield, but there has been no defin- Depending on the latitude of the Aquaculture Research 36:264- itive demonstration of this effect. pond, the length of the growout 277. phase may be 110 to 170 days. References Wurts, W.A. and R.M. Durborow. Harvest should be planned when 1992. Interactions of pH, car- daily water temperatures range Brunson, M.W., C.G. Lutz and bon dioxide, alkalinity, and from 62 to 68 degrees F for 4 to 5 R.M. Durborow. 1994. Algae hardness in fish ponds. days, or before an anticipated cold blooms in commercial fish Southern Regional front may cause lethal water tem- production farms. Southern Aquaculture Center (SRAC) peratures (≤ 55 degrees F) to Regional Aquaculture Center Publication No. 464. occur. Harvest is most efficient in (SRAC) Publication No. 466.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not been revised are considered to reflect the current state of knowledge.

The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No. 2003-38500-12997 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.