Procambarid Crawfish: Life History and Biology

SRAC Publication No. 2403

VI September 2007 PR

Procambarid Crawfish: Life History and Biology

W. Ray McClain1 and Robert P. Romaire2 Crawfish (or crayfish) have social, dering the Gulf of Mexico from Texas favorable. The red swamp crawfish economic and ecological significance to Alabama, northward up the Missis- produces more, but smaller, eggs in several regions around the world, sippi River drainage into Tennessee than the white river crawfish. The including the southern United States. and Illinois, and southward into east- red swamp crawfish appears to be Louisiana dominates the crawfish ern Mexico. The red swamp crawfish better adapted to nutrient-rich waters industry of North America in both has been introduced in other areas of and may tolerate higher water tem- aquaculture and wild capture fish- the U.S. (including Hawaii) and in at peratures, although these differences eries. Crawfish also are cultivated for least 19 other countries in Central have not been confirmed. The white food in Texas, Arkansas, Mississippi, and South America, the Caribbean, river crawfish grows faster at cooler Alabama, South Carolina and North Europe, Africa and Asia. The white temperatures and can attain a slight- Carolina, and are consumed in these river crawfish is found in the south- ly higher maximum size of about 130 and many other states. However, ern states along the Gulf of Mexico grams (3.5 crawfish per pound). there is no place where crawfish and northward up the Mississippi Anecdotal evidence indicates that the have had more impact on the econo- River drainage, possibly as far as the red swamp crawfish is usually more my of a region than in Louisiana, confluence of the Mississippi and abundant in standing water habitats where the industry contributes well Ohio Rivers. The eastern white river with low dissolved oxygen, such as in excess of $150 million to the crawfish is found along the Atlantic swamps. Hence the common name state’s economy annually. coastal plain into southern New red swamp crawfish. England. Both red swamp and white river Species of importance The red swamp and white river crawfishes do well in commercial Procambarus clarkii (the red swamp crawfishes, and to a lesser extent the crawfish ponds, and both thrive in crawfish) and P. zonangulus (the eastern white river crawfish, have the low-energy-input, extensive aqua- white river crawfish) are the species similar ecological requirements. The culture systems used in Louisiana of greatest commercial importance in red swamp and white river crawfish- and other southern states. Though the southern U.S. Procambarus acutus es often co-exist in the same native the abundance of each species can acutus, sometimes referred to as the habitat or managed impoundment. vary among ponds and within a pond eastern white river crawfish, is culti- Both are ecologically adapted to the during the 7- to 10-month production vated in several states along the east annual hydrological cycles of spring cycle, the red swamp crawfish most coast of the U.S. and is nearly indis- flooding and summer dry periods often dominates the catch and is the tinguishable from P. zonangulus. common to large river systems and most desired species in the market- These crawfishes belong to the phy- floodplains in the region. Both place, particularly in Louisiana. lum Arthropoda (subphylum species construct simple shallow bur- White river crawfish are usually Crustacea), order Decapoda, and rows, to which they retreat to repro- most numerous in ponds that have family Cambaridae. The red swamp duce and survive temporary dry peri- been in continuous cultivation for crawfish is native to the states bor- ods. One notable difference between several years; it occasionally becomes the two species is that, in the South, the dominant species over time. the white river crawfish is a seasonal The factors that govern the relative 1 Rice Research Station, Louisiana State spawner, reproducing only in the fall abundance of the two species in University Agricultural Center and winter. Red swamp crawfish may production ponds are not fully 2 Aquaculture Research Station, Louisiana State spawn at any time during the year University Agricultural Center understood. Research has shown when environmental conditions are that the species that enters the pond first in greatest numbers after As the common names suggest, south (2 years or less), have relatively fall flood-up is likely to dominate adults of the white river crawfish are high juvenile survival rates, and can the population. Thus, if red swamp off-white to tan, while the adult red alternate between sexually active and crawfish become established first swamp crawfish is red. However, inactive forms. P. clarkii can spawn after the pond is flooded, they will color alone is not a definitive distin- year-round in the southern U.S. and dominate the population and the guishing characteristic, particularly in females may reproduce more than later harvest. If juvenile white river immature crawfish. The large prima- once a year. ry claws or “chelae” of adult white crawfish become established before The life cycles of both red swamp river crawfish are more elongated red swamp crawfish juveniles enter crawfish and white river crawfish and narrow than those of adult red the population, white river craw- have evolved to allow them to adapt swamp crawfish. The areola, or space fish will dominate the population to the cyclical low-water dry condi- on the dorsal surface where the two and the subsequent catch. Despite tions and high-water flood conditions halves of the carapace meet, is wider efforts to limit the presence of common to their natural habitats. on white river crawfish. Also, the white river crawfish in ponds in Commercial crawfish aquaculture white river crawfish lacks the dark Louisiana (because it is less desir- simulates this hydrological cycle, but stripe on the underside of the tail or able in the marketplace), both with precise control over when ponds abdomen that is a distinguishing species are responsive to routine are flooded and when they are dewa- characteristic of red swamp crawfish. culture practices and often co-exist tered to optimize recruitment and sub- Sex is easy to distinguish in both in production ponds. sequent crawfish production. Mature species. Males have two sets of hard, There is no evidence that red swamp animals mate in open water and the calcified swimmerets next to the and white river crawfishes cross- sperm are stored in a seminal recepta- thorax; females have a seminal recep- breed naturally, although crossbreed- cle (annulus ventralis) on the underside tacle (annulus ventralis) and oviduct ing and hybridization have been of the female. The female may mate openings (Fig. 2). observed in other crawfish species. with more than one male and eventu- The red swamp and white river Life cycle ally retreats to the burrow to spawn. crawfishes are similar in appearance, Although spawning can take place in especially at a young age, and an Based on their distribution in North open water, the burrow provides pro- inexperienced observer might not be America, the red swamp and white tection while the eggs and offspring able to distinguish between the two river crawfishes are classified as tem- are attached to the abdomen. Females species. Several key anatomical fea- perate species; however, aquacultur- carrying eggs or hatchlings are highly tures are used to distinguish between ists generally regard them as having vulnerable to predators because the them (Fig. 1). traits normally associated with attached brood prevents the typical warmwater species. These crawfishes escape response, which is repeatedly are relatively short-lived in the deep

SR

CS

Figure 1. Adult white river crawfish (Procambarus zonangulus), top left, have longer, narrower claws than red swamp crawfish (Procambarus Figure 2. Males (left) can be recognized by two pairs of hard, calcified swim- clarkii), top right. Red swamp craw- merets (CS) next to the thorax and spur-like protrusions at the base of the fish (bottom right) usually have a middle set of walking legs. On females (right), the seminal receptacle (SR) can dark line visible on the underside of be observed on the underside of the thorax between the last pair of walking the abdomen, whereas the white legs; with close observation, the oviduct openings can be spotted near the river crawfish do not. basal joints on the second pair of walking legs. and rapidly contracting the tail to propel itself backward very quickly. Crawfish can burrow for reproduc- tion at any time of the year but do so most often in late spring/early sum- mer in the South. Crawfish of all ages and sizes, whether mature or immature, male or female, will con- struct burrows or retreat to existing burrows to survive periods of dewa- Figure 4. Extracted crawfish ovaries Figure 5. Female with hatchlings tering. Crawfish ponds are usually showing the various stages of maturi- attached to swimmerets beneath the drained from late April in some pro- ty, from well developed on the left to abdomen. duction systems to as late as July or immature on the far right. August in others. Before draining, mature crawfish burrow near the become separated from the female as water line (Fig. 3). As the water level been stored in the seminal receptacle, drops, crawfish burrows follow the she moves about in open water and and then are attached to the swim- they disperse in the pond. waterline. Some burrows are found merets (pleopods) under the tail on the pond bottom after draining, (abdomen) with an adhesive sub- Because spawning is largely syn- but those often contain a high per- stance called glair. Although crawfish chronized in pond-reared crawfish, centage of non-reproductive craw- can survive in a very humid environ- production ponds are routinely fish, such as males and immatures. ment within the burrow, they must flooded in autumn to coincide with For unknown reasons, some individ- have free-standing water for spawn- peak spawning. The spawning of uals will not burrow as the habitat ing. The number of eggs laid varies both red swamp and white river dries, while others will construct with the size and condition of the crawfish peaks in autumn and usu- very shallow burrows that can quick- female and usually ranges from 200 ally several waves of young-of-the- ly dry out and lead to death. to 300. Large females (more than year emerge with pond flooding In mature females, eggs usually about 15 count, 30 g) can have more and rainfall. Continuous recruit- begin to develop before burrowing than 500 eggs. ment and differential growth result and complete development in the in a crawfish population of mixed The incubation period is temperature sizes and age classes. burrow. As they mature, eggs within dependent and it takes about 3 weeks the ovary become spherical, enlarge, for eggs to hatch at 74 °F. Hatchling A crawfish must molt or shed its and change color from white or crawfish remain attached to the hard exoskeleton to increase in size cream to dark brown (Fig. 4). At female’s swimmerets through two (Fig. 6). Frequent molting and rapid maturity, the large, dark eggs are molts, after which they closely growth occur in production ponds expelled through the oviducts, fertil- resemble adults in appearance. After when conditions are suitable. Growth ized externally with sperm that have hatchlings become detached from the rate is affected by many factors, female, they tend to remain with her including water temperature, popula- for several more weeks. It is critical tion density, dissolved oxygen levels, that the female and her young leave food quality and quantity, and genetic the burrow within a reasonable time influences; however, environmental after spawning because little food is factors have the most influence on available in burrows and cannibalism growth rate. Harvest size is typically and death of the young can otherwise reached within 3 to 5 months after occur. hatching in the South, but it can be Pond flooding, in combination with rainfall, allows crawfish to emerge from burrows. Crawfish are trapped inside the burrow by the dried soil plug at the entrance. There must be enough external moisture to soften the plug before crawfish can emerge. When burrows are flooded, crawfish can emerge, but when crawfish have burrowed above the water line on Figure 3. Crawfish burrows appear levees, they may not be able to near the water line in ponds when emerge until there is heavy rainfall to mature crawfish begin burrowing for soften the soil plug. It is common for reproduction. Burrows may or may not the brood female to emerge with have the typical “chimney” associated young or eggs attached to the abdo- with the entrance. The density of bur- men (Fig. 5). Hatchlings quickly Figure 6. Soft, freshly molted crawfish rows in this photo is extremely high. (top) and its cast exoskeleton (bottom). reached sooner with optimal growing tions, but it is thought that any free lengthy dry periods or drought. Soil conditions. water in a burrow is likely to be with little clay content and soil with After growing and attaining sexual trapped water, perhaps from rainfall very high clay content that cracks maturity, both males and females seepage, rather than water seeping during severe drought may also make stop growing. Sexually mature indi- into the burrow from the water table. it difficult to survive if moisture is viduals have distinct sexual charac- When there is no standing water in lost during burrow occupation. teristics, including darker color, the burrow, wet mud in the chamber enlarged claws (chelae), and hard- serves as a humidifier. This can sus- Molting ened sexual structures. Mature males tain crawfish but is not conductive to Molting is the process by which develop prominent hooks at the base spawning. The burrow walls and ter- crawfish shed their old exoskeletons of the third and fourth pair of walk- minal chamber are extensively to grow. Crawfish grow during short ing legs (pereipods) and there are worked by the crawfish, possibly to episodes of molting with long inter- changes in the seminal receptacle of ensure good seals. The entrance of molt periods between each shedding mature females. Mature individuals the burrow, which often has a chim- episode. Young crawfish must molt become more abundant in late ney or stack of the excavated soil, is about eleven times to reach maturity. spring. Females will mate after their eventually closed with a mud plug A molt cycle has five major stages, maturity molt and begin the process (Fig. 7). Burrow entrances at the but the process is actually a continu- of constructing burrows at the water’s edge are often hidden under um with indistinct delineations. The water’s edge on levees. vegetation or woody debris. Over intermolt phase is the period when time, the burrow entrance may the exoskeleton is fully formed and Burrow ecology become undetectable because of hardened. During this phase, craw- weathering and vegetative growth. Although procambarid crawfish can fish eat and increase tissue and ener- construct burrows underwater, this gy reserves. Preparation for molting rarely occurs in commercial craw- takes place in the premolt stage. fish ponds in the South. One excep- During premolt, a new underlying tion is when a severe cold front (soft) exoskeleton forms while miner- rapidly lowers the water tempera- als from the old shell are reabsorbed. ture in shallow ponds. Then, craw- During the late premolt period, craw- fish will sometimes dig shallow fish stop feeding and seek shelter burrows underwater in the pond because they are particularly vulner- bottom, presumably to buffer the able to predation and cannibalism effect of a drastic temperature during molting. The molting or decline. Normally, however, bur- “ecdysis” phase involves the actual rows are built above the water line, shedding of the old exoskeleton and usually at the water’s edge, and in takes only minutes to occur. The brit- some cases in small puddles of Figure 7. Active crawfish burrows tle exoskeleton splits between the will eventually become sealed with a water away from the water’s edge. head (carapace) and tail (abdomen) soil plug or cap. With time and on the dorsal or back side, and the Burrows must be constructed in weather, and covering by vegetation, saturated soil because the process crawfish usually withdraws from the the burrow entrance may become old exoskeleton by tail flipping. It is involves creating a soil slurry, inconspicuous. which is removed from the hole in during the soft phase that the new, multiple trips to form the burrow. supple exoskeleton expands to its new dimensions. Calcification or Procambarid crawfish dig simple, Burrows usually contain either a sin- “hardening” of the new exoskeleton nearly vertical burrows, usually 40 gle female or a male and female. takes place during the postmolt phase, inches or less in depth. Burrows are Occasionally, a burrow may contain which can be divided into two peri- a refuge from predators and provide a single male or more than two ods. Initial hardening occurs when the moist, humid environment neces- crawfish. Burrows are usually occu- calcium stores within the body are sary for crawfish to survive dry peri- pied for several months before craw- transported to the new exoskeleton. ods. These species of crawfish have fish emerge with the presence of Calcium is stored in the body in soft evolved to spawn within the protec- water. Survival during the time they tissue, in blood and, for a short peri- tion of the burrow. Most burrows are are in the burrow depends on the od, in two hard “stones” or gastro- built at night and may require sever- severity and length of the dry inter- liths (Fig. 8) located in the head on al days to complete. Crawfish bur- val (which is associated with burrow each side of the stomach. The gastro- rows are usually dug by an individ- moisture), characteristics of the bur- liths disappear as they dissolve and ual crawfish, with the burrow diame- row (such as depth and soil type), the minerals are reabsorbed after ter determined by the size of the and the health of the animal. molting. The second period of shell crawfish. The burrow extends down- Immature crawfish and crawfish hardening is absorption of calcium ward into a terminal chamber that is forced to burrow by rapidly declin- from the water. As crawfish resume slightly larger than the diameter of ing water levels may construct shal- feeding, further mineralization and the tunnel. Water levels in burrows low burrows that do not retain suffi- hardening of the new exoskeleton vary with the soil moisture condi- cient moisture for survival during occur. Food habits These animals, when consumed by crawfish, are a source of high-quality Crawfish have been classified as her- nutrition. For crawfish to grow at bivores (vegetation eaters), detriti- their maximum rate, they must con- vores (consumers of decomposing sume animal matter or other high- matter), omnivores (consumers of protein and energy-rich foods. both plant and animal matter), and, However, they can sustain them- more recently, as obligate carnivores, selves for some time by eating intact which means that they “require” and detrital plants and bottom sedi- some animal matter in the diet for ments containing organic debris. optimal growth and health. Crawfish have been known to ingest living Supplemental feeds are not routinely and decomposing plant matter, seeds, used in most commercial crawfish algae, microorganisms, and an assort- aquaculture ponds. Instead, produc- ment of larger invertebrates. They ers establish or encourage a forage will also eat some vertebrates such crop to provide the basis of a com- as small fish, but food resources vary plex food web (Fig. 10) from which considerably among habitats. Living crawfish derive most of their nutri- plants, often the most abundant food tional needs. Plant fragments from Figure 8. Gastroliths, paired bodies resource in crawfish ponds and in the forage crop provide the “fuel” formed within the wall of the foregut that drives a detrital-based produc- (“stomach”) during the premolt natural habitats, are thought to con- tribute little to the direct nourish- tion system, with crawfish at the top phase, store minerals from the old of the food web. Juvenile crawfish exoskeleton during molting. ment of crawfish. Starchy seeds, if present, are consumed and may pro- also derive some nutritional value vide needed energy. They mostly eat from residual bait associated with harvesting activities. Molting is controlled by hormones intact fibrous plant matter when other food sources are in short sup- and occurs more frequently in Water quality younger crawfish than in older ones. ply; aside from furnishing some The amount of growth that occurs essential nutrients, it provides a lim- Water quality management in craw- during molting and the intermolt ited amount of energy and macro- fish production usually focuses on interval (or period between molts) nutrients to growing crawfish. maintaining acceptable levels of dis- can vary greatly; growth is affected Decomposing plant material, with its solved oxygen. Procambarid crawfish mostly by environmental factors associated microorganisms (collec- are generally tolerant of low oxygen such as water temperature, water tively referred to as detritus), is con- levels, but persistent exposure to quality, food quality and quantity, sumed in greater quantity and has a extremely low oxygen concentrations and crawfish density. Research indi- higher food value, but detritus does can reduce production. Juveniles are cates that genetics plays a minor role not generally provide the protein and most susceptible to chronically low in growth. Crawfish can increase up energy needed for maximum growth. levels. When dissolved oxygen to 15 percent in length and 40 per- In the aquatic environment, there remains consistently below 1 ppm cent in weight in a single molt under are many other animals that rely on throughout the day for several optimal conditions. microbial-rich detritus as a primary weeks, crawfish become sufficiently food source, including mollusks, stressed that they may stop feeding. After a period of growth, both males Levels consistently below 0.5 ppm and females molt to a sexually active insects, worms, small crustaceans and some small vertebrates (Fig. 9). may affect molting and reduce craw- phase (referred to as Form I phase) fish survival. Other important water and growth ceases. In southern aqua- quality variables are pH, total hard- culture ponds, frequent molting and ness, total alkalinity, iron, hydrogen rapid growth occur in spring because sulfide content, ammonia, nitrite and of warming waters and adequate salinity (salt content). Desirable val- food sources. More mature crawfish ues are between 6.5 and 8.5 for pH, appear as the season progresses. more than 50 ppm as CaCO3 for High temperatures (> 80 °F) when total hardness, more than 50 ppm as crawfish are overcrowded and food CaCO3 for total alkalinity, less than is scarce may stimulate the onset of 0.1 ppm for ferrous iron, less than maturity at a smaller than desirable 0.002 ppm for hydrogen sulfide, less market size. This is referred to as than 0.06 ppm for un-ionized ammo- “stunting.” When moved to a better nia, less than 0.6 ppm for nitrite, and environment, a stunted crawfish may Figure 9. Invertebrates in crawfish less than 6 ppt for salinity. revert to a sub-adult form (Form II) ponds, fed by decomposing plant and resume growth. fragments, furnish crawfish with the high-quality nourishment needed for maximum growth. oxygen is low. The only practices related to disease management in the procambarid crawfish industry are those which minimize food shortages, overcrowding, and exposure to low dissolved oxygen. All North American crawfishes are suspected to be vectors of the Aphanomyces fungi, or plaque fun- gus, which was responsible for dramatically reducing or eradicat- ing populations of Noble crawfish (Astacus astacus) in many lakes, rivers and streams throughout Europe. Although known to be carriers of the fungus, North American crawfishes are not nor- mally affected by the fungus. Figure 10. A simplified diagram of the nutrient pathways of the food web in Procambarid crawfish cultured in crawfish ponds, with the forage crop serving as the principal fuel and crawfish the southern U.S. are sometimes at the top of the food chain. affected by other organisms that do not necessarily have an effect on production but may hinder crawfish Parasites and diseases in commercial crawfish aquacul- marketability because of certain ture operations for the first time in physical effects. Microsporida—a Serious disease problems in pro- 2007. The disease occurred in microscopic protozoan—can infest cambarid crawfish culture, as cur- Louisiana but its prevalence and the abdominal muscle, giving it an rently practiced in the southern impact on crawfish production is unattractive milky-white appear- U.S., have been rare. Individual not yet known. The rarity of dis- ance (porcelain disease), but this is crawfish are susceptible to various ease outbreaks in crawfish aqua- not common and has minor eco- pathogens such as bacteria, virus- culture is presumably due to the nomic impact on the industry. es, fungi, protozoans and para- extensive nature of production sys- Various ectocommensal organisms sites; however, epidemic outbreaks tems. Significant disease problems that attach to the exoskeleton can sufficient to affect commercial are more likely to be encountered limit the acceptability of crawfish if production in earthen ponds have in intensive, high-density holding the infestation is heavy, and at not been encountered until recent- systems, such as purging opera- times buyers may refuse to accept ly. White spot syndrome virus, the tions and soft-shell production lots of crawfish with heavily soiled disease that has caused significant facilities. Diseases are also most exoskeletons. mortality on marine shrimp farms likely to occur when temperatures around the world, was identified are high and/or when dissolved

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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. 2005-38500-15815 from the United States Department of Agriculture, Cooperative State Research, Education, and Extension Service.