Although captive fisheries for introduced Procambarus clarkii exist in several other countries (such as China, Spain, and Portugal), there is no place where crayfish are more highly regarded socially and have had as much impact to the economy of a region than in the southern United States. Crawfish are cultivated and consumed for food in several southern states but Louisiana dominates the crawfish industry of North America in both aquaculture and wild capture fisheries, where the industry contributes well in excess of USD 150 million to the state's economy annually. Commercial sales of crawfish from natural waters began in Louisiana in the late 1800s, and with the development of improved transportation and cold storage, crawfish markets shifted from local consumption in rural areas to higher-volume markets in cities such as Baton Rouge and New Orleans, and beyond. Annual supplies of wild harvests were extremely variable from year to year and the season was often short-lived. Therefore, entrepreneurs began experimenting with the farming of crawfish by the mid 20th century as a source of more dependable supplies. Pond culture of crawfish soon became integrated with other farming operations, and today, pond-reared crawfish constitutes the majority of the annual harvest. Over the last decade, farm-reared crawfish have accounted for well over 75 percent of the total harvest. Approximately 48 000 ha are devoted to the culture of crawfish in Louisiana and the state accounts for about 90-95 percent of the total production in the USA.
At the time that this fact sheet was prepared, no information or documentation was available that indicated that China is intentionally culturing P. clarkii on a commercial scale, despite the large amount reported to FAO in its aquaculture statistics. It is possible that there are some culture ponds where P. clarkii are raised but we have no details on their number or size. It is believed that the crawfish exports from China are a result of both captured stocks (from rivers, streams, canals, etc.) and incidental catches from the seining of finfish ponds.
Procambarus clarkii was originally distributed from northern Mexico to Florida, and north to southern Illinois and Ohio. It has been widely introduced in the USA (Arizona, California, Georgia, Hawaii, Idaho, Indiana, Maryland, Nevada, New Mexico, North Carolina, Ohio, Oregon, South Carolina, Utah, Oklahoma), south and central America (Belize, Brazil, Costa Rica, Dominican Republic), Europe (Portugal, Spain, France, Cyprus), and other more dispersed areas (Japan, Kenya, China, Taiwan Province of China and Uganda).
P. clarkii is found in lentic and lotic freshwater habitats: sluggish streams and lentic habitats, swamps, ditches, sloughs and ponds, etc., especially in vegetation, leaf litter, etc. It avoids streams and ditches with a strong flow, where it is replaced by other species. It exhibits territorial behaviour and is aggressive with its own species. It burrows during periods of drought or cold. It is benthic and omnivorous, feeding on insects, larvae, detritus, etc., with a preference for animal matter. Procambarid crawfish in natural habitats have been classified as obligate carnivores, which means that while they can subsist on living and detrital plant matter they require some form of animal matter in the diet for optimal growth and health.
The life cycle of this burrowing crawfish is well suited to the annual sequence of spring flooding and summer dry period common to large river systems and floodplains in the southern USA where it is most abundant.
Mature animals mate in open water, and although spawning can take place in open water, the burrow provides protection while the eggs and offspring are attached to the abdomen. Burrowing activity for reproduction can occur at any time of the year but it is most prevalent in late spring/early summer in the South. Egg development in mature females usually begins prior to burrowing and maturity is completed in the burrow. At maturity, the eggs are expelled through the oviducts, fertilized externally with sperm that has been stored in the seminal receptacle, and are then attached to the swimmerets on the tail (abdomen). Although crawfish can survive in a high humid environment within the burrow, standing water is necessary for spawning. The number of eggs laid varies with size and condition of the female and will usually range from 200 to 500 eggs.
Hatchlings remain attached to the female's swimmerets through two moults, after which they become free and can forage on their own. It is a fast-growing species; in adequate conditions larvae are born after 21 days of incubation (5 mm long at 2 days), growing to 2 cm one month later and up to 80 mm of length in 3 months. It is an eurythermal species (10-22 ºC to >30 ºC) and inhabits all types of water, with a preference for hard water
Although the red swamp crawfish P. clarkii is the target species in most crawfish aquaculture ventures, other species have similar ecological requirements and often co-exist in production ponds. The native range of the P. zonangulus (white river crawfish) overlaps that of P. clarkii in the south-central United States, and introduced P. clarkii co-exists with the native P. acutus acutus (eastern white river crawfish) in culture ponds along the Atlantic coast. Though the abundance of each species can vary among ponds within a region and, to a lesser extent, within a pond during the annual production cycle, the red swamp crawfish usually dominates the catch and is the most desired species in the marketplace, particularly in Louisiana. White river crawfish are commonly found in greatest numbers in ponds that have been in continuous cultivation for several years. No evidence of natural crossbreeding has been observed. The main biological difference is that P. clarkii is capable of spawning year-round in the southern United States and the white river species are considered seasonal spawners.
Because spawning is to a large degree synchronized in pond-reared crawfish, production ponds are routinely flooded in autumn to coincide with peak spawning. Continuous recruitment and differential growth result in a crawfish population of mixed sizes and age classes. Frequent moulting and rapid growth occur in production ponds when conditions are suitable. After a period of growth, both males and females attain sexual maturity and growth ceases. Mature individuals typically increase in abundance in late spring and burrowing in earnest begins. Under favourable environmental conditions, mature crawfish may revert back to a sexually inactive form and continue growing.
Since crawfish populations are self-sustaining, stocking is usually needed only in new ponds, when a pond has been idle for a year or more or after extensive levee renovation. Subsequent crawfish crops rely on holdover broodstock from a previous cycle. Seedstock are simply composed of harvested red swamp crawfish either from natural habitats or culture ponds where a high percentage of the individuals are sexually mature.
As noted earlier, the life cycle of this burrowing crawfish is well suited to the annual sequence of spring flooding and summer dry period common to large river systems and floodplains in the southern USA where it is most abundant. Commercial crawfish aquaculture simulates this hydrological cycle, but with precise control over when ponds are flooded and when they are dewatered to optimize recruitment and subsequent crawfish harvests. The dried soil plugs at the burrow entrances become softened when sufficient external moisture is available. Thus, pond flooding, in combination with rainfall, allows the emergence of animals that have been trapped inside the burrows.
Procambarid crawfish aquaculture relies on earthen ponds and extensive methods of production. These methods are little more than limited control of the environmental conditions under which these animals evolved. Sustained periods of open water permit crawfish to feed, grow and mature. Temporary dewatering promotes aeration of bottom sediments, reduces abundance of aquatic predators, and allows for the establishment of vegetation that serves as cover for crawfish and the food resources when water is returned. Crawfish survive the dry intervals by digging or retreating to burrows where they can avoid predators, acquire the moisture necessary for survival and reproduce in safety.
Crawfish are grown in shallow earthen ponds 20 to 60 cm deep. Relatively flat, drainable land with clay soils is required. Water requirements are similar to those for other types of freshwater aquaculture, with the possible exception of water quantity, which can be greater. Ponds are flooded and drained each year, and because of the oxygen demand from decaying vegetation, additional water exchanges are sometimes necessary.
Production strategies for culturing crawfish are categorized by two basic approaches.
One strategy is monocropping (or monoculture) in which crawfish is the sole crop harvested, and production typically occurs in the same physical location for several production cycles or longer. A second strategy is the crop rotation system, in which rice, and sometimes other crops, is raised in rotation with crawfish. The crop rotation approach can be further broken down into two subcategories. Crawfish are either rotated with rice in the same physical location year after year, or crawfish are cultured in different locations each year to conform to normal field rotations of rice. Although these management strategies have many similarities, different production goals dictate different management techniques and have different advantages and disadvantages.
Crawfish monocropping (the 'single-crop' system) is the production method of choice for small farms or where marginal lands are available and unsuited to other crops. Permanent ponds are typically used. Pond size and production input may range from large (greater than 120 ha) impounded wetlands with little management to small (less than 6 ha) intensively managed systems. The main advantage of a monoculture strategy is that producers can manage for maximum crawfish production without the various concerns associated with other crops, such as pesticide exposure, seasonal limitations and other constraints associated with crop rotation.
Crawfish yields in monoculture systems typically range from less than 225 ha/kg in large, low input ponds to more than 1 300 kg/ha with intensive management. Some ponds have yielded in excess of 2 800 kg/ha. Smaller ponds usually have higher yields than larger ponds, especially when marketing of smaller, lower-value crawfish is not a problem. Earlier and more intense harvesting is often justified under this approach because of the dense populations that tend to build after several consecutive years of production. Earlier harvests are almost always associated with the highest seasonal prices.
The disadvantages of the monoculture approach often include:
Ponds are thoroughly drained several weeks after stocking and annually thereafter. Cultivated or volunteer vegetation is established in pond bottoms during the summer when ponds are dewatered. Rice is the standard cultivated crop, and emphasis is on forage (stem and leaf) production. Grain, if present, is not harvested in crawfish monoculture. After re-flooding in autumn, producers monitor the crawfish population with baited traps and initiate harvesting when catch and marketing conditions justify the labour and expense. Harvesting continues (often at intermittent intervals) until ponds are drained the following summer, and the cycle is repeated.
Crop rotational systems
Crawfish may be cultured in two basic crop rotation systems. One is rice-crawfish-rice; the other is rice-crawfish-fallow (or soybeans may be farmed following crawfish). In both strategies, crawfish culture follows the rice harvest, and the forage crop used for growing crawfish is the crop residue and re-growth of the rice stubble after grain harvesting. The advantages of these rotational strategies include efficient use of land, labour and farm equipment. Moreover, some fixed costs and the cost of the establishment of rice can be amortized over two or more crops instead of just one.
This approach takes advantage of the seasonality of each crop to obtain two crops in one year in the same field. Rice is grown and harvested during the summer, and crawfish are reared during autumn, winter and early spring. As with monoculture systems, crawfish are only stocked initially. They are introduced directly into the rice crop about 6 weeks post-planting. Following the grain harvest, the residual rice stubble is usually fertilized with a nitrogen-based fertilizer and irrigated to achieve a ratoon crop of forage. The field is flooded in autumn and management practices are then similar to in the monoculture system, with the exception of a shortened growing and harvesting season to accommodate the establishment of the next rice crop.
A major disadvantage with this rotational strategy is usually that neither crop can be managed to yield maximum production. Rice yields in the southern USA are maximized when rice is planted in early spring. Draining the crawfish pond prematurely to accommodate rice establishment decreases total crawfish yield. Pesticide use is another major management consideration, and it is a particular constraint with this production strategy. Crawfish and rice yields vary and depend on management emphasis. Systems managed mainly for crawfish can expect crawfish yields similar to well-managed monoculture systems but at the expense of rice yield and vice versa.
Rice-crawfish-fallow (or rice-crawfish-soybean)
The other major rotational strategy employs crawfish in a rotational system of rice and, sometimes, soybeans. The major difference in this rotation strategy is that rice is not typically cultivated in the same field during consecutive years, to aid in the control of rice diseases and weeds for maximum rice yield. As with a rice-crawfish-rice rotation, however, crawfish culture follows rice cultivation; therefore, crawfish production does not occur in the same physical location from one year to the next. Under this method, if soybeans or another crop is incorporated, three crops per field can be realized in two years. Depending on a variety of factors, some producers may elect to plant a different crop (hay, pasture or grain sorghum) or, more commonly, simply leave the field fallow instead of planting soybeans after the crawfish season ends.
The field rotational approach requires sufficient land resources to allow staggered crops in different fields within a farm, and it is the preferred cropping system for larger commercial rice farmers. This cropping strategy comprises much of the acreage used to grow crawfish in Louisiana. It has several advantages over rotation within the same field. Each crop can be better managed, and the crawfish production season can be extended. For example, in lieu of draining crawfish ponds in early spring to plant rice, crawfish harvest can continue until late spring or early summer when the pond is drained to plant soybeans (or other crops), or longer if plans are to leave the field fallow. Furthermore, by rotating physical locations each year, overpopulation of crawfish is rarely a problem, and crawfish size often is larger because of lower population densities.
Crawfish yields under this management approach are not commonly as high as in monoculture but, with proper management, yields can routinely exceed 1 000 kg/ha. Some disadvantages of this rotational strategy relative to crawfish production in permanent or semi-permanent ponds are:
Supplemental feeds are not routinely used in most commercial crawfish aquaculture. Rather, an established or encouraged forage crop serves to provide the basis of a food web from which crawfish derive most of their nutritional needs. Plant fragments from the forage crop provide the 'fuel' that drives a detrital-based production system, with crawfish at the top of the food web. Some nutritional value to juvenile crawfish may also be provided by residual bait fragments associated with harvesting activities.
The heavy vegetation cover, encompassing virtually the entire pond area of most crawfish ponds, limits the harvesting options. Seine harvesting, a common method for many aquaculture species, is ineffective. Additionally, since crawfish recruitment to the harvestable population is continual over much of the season, regular and frequent harvests are necessary, as opposed to the more common infrequent batch harvests. Furthermore, presence of soft (newly moulted) crawfish precludes most active harvest methods. Therefore, this industry relies solely on the passive technique of baited traps.
A wire-mesh, 3-sided 'pyramid-shaped' trap is designed for use in shallow water and is effective and efficient to operate. This trap is positioned upright in the pond with the top extending above water. The top is open to facilitate rapid removal of crawfish and re-baiting and contains a retainer collar that minimizes crawfish escape and serves as a handle. The size and shape of the mesh wire used to construct the trap governs the size of crawfish retained by the trap. Most traps are currently made of 1.9 cm plastic-coated square mesh that retain crawfish of 12 g (about 70 mm total length) and larger; however, consumer preferences are for crawfish larger than 20 g.
Two categories of bait are used to attract crawfish to the trap - natural baits of fish, and manufactured baits of proprietary formulations. Although more expensive, fish is the preferred and most effective bait at water temperatures below 20 ºC. Manufactured baits are most effective at temperatures above 20 ºC. Most baiting regimes are based on a 24 hour trap-set, but 12 and 48 hour (or longer) sets are sometimes used.
Traps are most effectively used when distributed throughout the pond and are normally set in rows to accommodate harvesting by boat. Most commercial ponds larger than 2 or 3 ha are harvested with the aid of a motorized, flat-bottom boat designed for shallow-water propulsion. Several boat types and propulsion designs are available, but the most widely used apparatus consists of an aluminium boat equipped with a hydraulically driven metal wheel that extends beyond the boat and either pushes or pulls it through the pond. A gasoline engine inside the boat powers a hydraulic system for propelling and steering it. Commonly, the boat travels down the lanes of traps and a fisherman (sometimes two) will empty and re-bait each trap from one side of the boat, often without stopping at the traps.
Trap density can range from 20-60/ha, depending on intensity of the operation. Harvesting begins as soon as the catch is justifiable - usually 2 to 4 months after flooding. Trapping frequency and duration also varies. Traps are emptied 2-7 days/ week, often intermittently for 3 to 8 months. Frequency and duration of the harvest are influenced largely by cost of harvesting, marketing price, and catch. The daily catch is determined by crawfish population density and structure, trapping effort, indigenous food resources, bait quantity and quality, and environmental conditions, but rarely exceeds 1.0 kg/trap/day on a sustained basis.
Most crawfish are sold to wholesale buyers, especially in Louisiana, although some are sold directly to restaurants and to retail customers. Nevertheless, all initial sales and a major portion of the final sales are for live crawfish. The favoured method for transporting and storing live crawfish is in open-mesh plastic sacks that hold approximately 18 kg of crawfish. This method is preferred over more rigid containers because crawfish can be easily packed in the sacks, such that when restricted, less damage is inflicted on one another with their chelae. Crawfish in good health can be stored at moist temperatures of 4-8 ºC for up to 6 or 7 days without excessive mortality.
Because the demand and price differentials for live crawfish favour the larger animals, grading by size has become a routine practice in some markets. Although the practice is common, there is not a commonly accepted grade standard for sized crawfish. Based on a number of production and marketing conditions, crawfish, when sized, are graded into two or three classes. Generally, the largest crawfish are sold to speciality restaurants, and the smaller ones are processed for the abdominal meat or blended with larger individuals for large volume sales. Nearly all grading occurs at wholesaling outlets or processing plants, using modified vegetable or self-built graders. Producers are usually paid according to yield by size class, and the largest class can sometimes bring five times more per kilo than the smallest grades.
Notwithstanding the size and significance of the crawfish aquaculture industry today, few people make their sole living culturing crawfish - it is still mostly a secondary enterprise. Rice farmers comprise the largest share of commercial crawfish producers, but detailed budgets amortizing production costs over each crop is lacking. Moreover, because of the extensive attributes of crawfish farming and the secondary nature of these enterprises, few detailed records are maintained, thus production costs are variable and largely unknown. Harvesting is the most labour intensive component of crawfish farming, however, and typically 50-70 percent of total direct expenses are associated with the harvest. Bait and the labour required for trapping are the greatest expenses.
Serious disease problems in procambarid crawfish aquaculture are rare. Individuals will occasionally exhibit disease symptoms, but epidemic outbreaks in earthen ponds have not been demonstrated. Crawfish are sometimes affected by agents that hinder marketability, usually as a result of heavily soiled exoskeletons. Because of the insignificance of diseases in pond culture, disease management is not deliberate. Practices that prevent food shortages, overcrowding and low oxygen (common stressors) are the extent of practices related to disease management in the crawfish industry and are referred to as Improved Husbandry (IH) in the table below. It should be noted, however, that all North American crawfish are suspected vectors of the crayfish plague fungus (Aphanomyces astaci) that was notorious for eliminating many populations of native European crayfish. Although carriers, North American crawfish are not normally affected by the fungus.
Suppliers of pathology expertise
There are few individuals that specialize in or have extensive knowledge about diseases of crayfish, especially with regard to the cultured procambarid species. The few experts usually reside in government and/or university laboratories in States within the southern USA where crawfish are grown commercially. The persons with the most extensive experience with Procambarus clarkii are:
Up to 2002 almost all of the reported aquaculture production of this species originated from the USA. The level of output from this country is extremely variable, depending mainly on climatological conditions. For example, in the period 1993-2002, it reached peaks of 26 375 tonnes in 1995 and 27 825 tonnes in 2002 but troughs of 7 713 tonnes in 2000 and 13 847 tonnes in 2001. USA production expanded again in 2003 to 33 498 tonnes and remained almost as high in 2004 but fell to a reported 16 355 tonnes in 2005. At its most recent peak (2003) USA production of red swamp crawfish was valued at USD 48.6 million, somewhat less than the value of the considerably lower tonnage of 2002 (USD 50.4 million).
In 2003, the statistical returns of China to FAO started recording a significant aquaculture production of red swamp crawfish. Nearly 51 600 tonnes in 2003, it had risen to over 88 000 tonnes by 2005, with a value exceeding USD 303 million, bringing the global aquaculture production of this species in that year to nearly 105 000 tonnes. However, there is some controversy concerning the production reported by China, which may not all be the product of aquaculture practices. It is hoped that this matter can be resolved by the time this fact sheet is updated.
Apart from the USA and China, no other countries reported aquaculture production of this species in 2005. However, fisheries exist in Kenya, Portugal and Spain and four countries (Costa Rica, Mexico, Spain and Zambia) are shown in the aquaculture geographical distribution map shown earlier in this fact sheet because they had reported aquaculture production to FAO in earlier years.
Whether from aquaculture or the natural fishery, the supply of live crawfish is highly seasonal, with the peak of the harvest in Louisiana occurring from March through June. Historically, most of the domestic supply in the USA has been consumed in Louisiana and surrounding southern states, particularly Texas, the Mississippi Gulf Coast, and the Florida Panhandle. Because of restricted geographical areas of production, seasonal supply, unstable prices and cultural mores, crawfish sales nationally have been limited. National sales have increased in recent years, but mainly from frozen or processed products. Import of live P. clarkii into some states outside of its native range, as into many countries, are prohibited because of ecological concerns.
Live crawfish demand the highest prices in the southern United States, but when there is an overabundance of crawfish and live markets become saturated, crawfish are processed and sold as fresh or frozen product. One product is cooked and frozen whole crawfish. The most popular product, however, is cooked, hand peeled, and deveined abdominal or 'tail' meat. This may be packed with or without hepatopancreatic tissue, which is an important ingredient in Louisiana (Cajun) cuisine. Meat yield varies with factors such as sexual maturity and age, but in general, cooked abdominal meat yield is about 15 percent of live weight. The amount of crawfish processed in Louisiana is variable from year to year, but in recent years, significant imports of crawfish meat from China have displaced much of the demand for Louisiana product.
Supply and demand relationships are reflected in price variations from year to year and from week to week during the USA crawfish harvest season. Seasonally, prices to producers are highest in winter and early spring when supply is relatively low. Prices typically decline significantly in late spring and summer when supply peaks and the supply and demand for other locally produced fresh seafoods, such as shrimp and crabs, increase.
Crawfish aquaculture as practiced in the southern USA represents one of the strongest agricultural entrepreneurial opportunities there. At a time when profits of many of the traditional agronomic and animal industries are declining, potential for crawfish aquaculture remains strong. Though not without its difficulties and constraints, crawfish aquaculture seems to be the choice for many farmers struggling with other crops, as well as the occasional landowner who wants to incorporate a harvestable crop with conservational and recreational land uses. This extensive approach to aquaculture continues to be an effective strategy for traditional and part-time farmers because of the relatively low-input and non-technical requirements. Notwithstanding these minimal requirements, crawfish aquaculture is also suited to the progressive producers who realize the profit potential when operations are well managed.
The long-term prospect for crawfish aquaculture, especially as practiced in forage-based systems, is sound because this approach is perhaps one of the most legitimate models for low-input, sustainable aquaculture. While no commercial agriculture system is genuinely sustainable without some additional inputs, crawfish aquaculture approaches this academic vision. Forage-based crawfish production systems exemplify judicious use of resources with minimal environmental impacts while providing sound economic benefits to communities. Moreover, these production systems provide substantial artificial wetlands, an important aquatic habitat for wildlife, and a suitable replacement for much of the diminishing natural wetlands.
Global expansion of the red swamp crawfish in pond culture is unlikely due to the concerns associated with non-native introductions of exotic species in general and this species in particular. P. clarkii has been introduced in a number of countries, usually with deleterious results on the environment. Further expansion of production in the southern USA will be governed by the expansion of additional marketing opportunities and possibly processing technology. Currently, the processing of crawfish is accomplished by non-mechanical means, and mechanical processing technology may be the key to increased markets and market share of products in the USA.
In Louisiana and the surrounding states, where nearly 100 percent of P. clarkii are pond cultured in the USA, crawfish aquaculture poses a minimal threat to the environment. This species is native to this region and management practices are relatively benign. Crawfish effluent water is usually low in nutrients and oxygen demand, but turbidity and suspended solids can be elevated at certain times of the year. Best Management Practices (BMPs) have been identified that will minimize potential impact of crawfish pond effluent on the environment, and producers are beginning to adopt these on a volunteer basis. Moreover, crawfish ponds serve as favourable wetland habitats to many species of waterfowl, wading birds, and furbearers, in additional to providing a highly valued and desirable seafood product. Integration of crawfish aquaculture with traditional agricultural land uses also serves as a practical means of land and water conservation.
Serious issues arise when P. clarkii or other crayfish species are introduced to regions outside of their natural range. The red swamp crawfish is very hardy and adaptive and has wreaked havoc in several ecological sensitive habitats. It can out-compete some aquatic species of an ecosystem and cause irrevocable harm to key plants and, as observed in Europe, can act as a vector of diseases. Its burrowing characteristics may also damage crops and earthen water holding structures.
A significant red swamp crawfish population now exists in China, where it is relatively widespread in the southern region. As long as there is a market for this species, its fishery there is likely to continue. It is unclear to what extent crawfish is or may be raised under a traditional aquaculture approach because of its relatively low yield potential and the apparent abundance of feral populations of crawfish. It is theorized that many piscivorous fish, birds, and mammals have been diminished in much of China's inland waters, providing ample opportunity for crawfish to thrive. Thus, with crawfish so abundant in native waters, there seems to be little incentive for expansion of aquaculture there - at least in the near future.
Because red swamp crawfish can readily escape from aquaculture facilities and establish populations in diverse habitats, often damaging aquatic ecosystems, and because they can vector diseases, such as the crayfish plague fungus (Aphanomyces astaci), aquaculture operations should not be conducted in areas where this species is not native or well established. Responsible aquaculture practices should also include the incorporation of conservation and environmental best management practices (BMPs) to conserve resources (water and energy) and limit pollution from effluents. Adherence to the FAO Code of Conduct for Responsible Fisheries is advisable.
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