Crayfish also called Crawfish or Crawdad, are crustaceans in which most of them live in freshwater and a few live in brackish or salt water. Some live in burrows on land close to a source of water, all crayfish have the ability to borrow (Hyman 1996). The freshwater crayfish live in lakes and rivers. Most crayfish tend to hide under rocks or logs during the daytime and are most active at night.
Crayfish belong to the kingdom Animalia, phylum Arthropoda, and class Crustacea. Crayfish belong to the infraorder Astacidea (Crayfish, 1995). They belong to the order Decapoda and can be grouped into three different families according to where they are found. Crayfish found in the Northern Hemisphere are in the family Astacidae and if they are found in the Southern Hemisphere they are in either the family Parastacidae or Austoastracidae, mostly found in Australia (Grzimek 1968). They are related to Spiny Lobsters and Lobsters.
Crayfish have a hard exoskeleton made from calcium. This exoskeleton protects the internal tissues from injury. The exoskeleton of crayfish can be a variety of different colors ranging from white to pink, orange, brown, to greenish-blue or dark blue (Barnard 1990). Crayfish are characterized by a joined head and thorax region and a segmented abdomen possessing moveable parts. Attached to the head is a pair of stalked eyes, branched antennae, a pair of long antennae and three sets of feeding appendages located near the mouth. Along the thorax are three pairs of appendages called maxillipeds, which are attached to the jaw so they may aide the crayfish in eating (Hyman 1996). The thorax also has five pairs of walking legs attached to it which are used for locomotion. The first pair of these legs is called chelipeds, or pinchers which are used to catch and hold prey and also for defense against predators. On the underside of the abdomen are six pairs of swimmerets that are used for swimming. In the female crayfish, the first pair of swimmerets are much smaller than the males’, because the males are modified for the transfer of sperm. Extending from the end of the abdomen are tail fins. Crayfish are usually around 6-8cm long, the smallest being 2.5cm long belonging to the species Cambarellus diminutus of southeastern United States, and the largest being around 40cm from the species Astacopsis gouldi from Tasmania (Encyclopedia Britannica Online A, 2000).
The brain of the crayfish is very complex for such a small animal. They have two head appendages, Antenna I and Antenna II. They have six major nerve roots, anterior median nerve, oculomotor nerve, antenna I nerve, antenna II nerve, tegumentary nerve, and the posterior median nerve. The brain of a crayfish can be divided into three sections, the Protocerebrum, deutocerebrum, and tritocerebrum. The Protocerebrum has three parts, optic ganglia, lateral protocerebrum and the median protocerebrum. The deutocerebrum has six parts, olfactory lobe, lateral antenna I neuropil, median antenna I neuropil, accessory lobes, deutocerebral commisure neuropil, and the olfactory globualr tract neuropil. The Tritocerebrum has two parts, the antenna II neuropil and the tegumentary neuropil. The brain of a crayfish has five tracts and commissures and 17 clusters of cell bodies. The brain of crayfish and spiny lobsters is dominated by four major parts, the antenna I and II neuropil, olfactory lobes and especially the accessory lobes (Sandman et. al., 1992).
Crayfish are regarded as scavenger feeders. They eat all kinds of vegetation and various types of animal foods including snails, small fish, insect larvae, worms and tadpoles. Crayfish are most active at night which is when they hunt for food. During the day crayfish can be found hiding under rocks and logs in the water. The crayfish that live in burrows hide in them during the day and only come out to hunt when there is enough water at the surface.
Crayfish make stones of calcium salt in their stomachs which are saved until the crayfish molts its exoskeleton. Once the exoskeleton is shed the stones are absorbed by the animal and are used in the making a new exoskeleton (Encyclopedia Britannica Online C, 2000). Another interesting fact about crayfish is that they excrete about five percent of their body weight in urine in one day (Encyclopedia Britannica Online B, 2000).
Reproduction of crayfish occurs in the late summer and early fall. The male crayfish takes the female and flips her over on her back and he then transfers sperm to the seminal receptacle located within her thorax (Hyman, 1996). The female lays her eggs in the spring which are fertilized when they pass over the seminal receptacle. After she cleans her abdomen out she secretes a sticky substance and attaches the eggs with this to her swimmerets (Hyman, 1996). The eggs then hatch about five to eight weeks later. The larvae remain attached to their mother for several weeks before they take off for free existence. Sexual maturity of crayfish can take as little as a month to reach or as long as several years. Crayfish molt many times during their lifetime before they reach their adult state. Crayfish can live from 1 to 20 years, this all depends on what species they belong to.
Crayfish do take up oxygen from the water through their exoskeleton by means of gills. There have been experiments performed by Ellis and Morris to observe how the pH effected oxygen consumption and uptake and metabolic activity in the Australian crayfish Cherax destructor. It was believed that more acidic or basic water would increase the energy expenditure in order to maintain homeostasis (Ellis and Morris, 1995). The results showed that the crayfish exposed to acidic water (pH 4.5) had a 79% reduction in oxygen uptake and crayfish exposed to basic water (pH 8.0) had a 53% reduction in oxygen uptake, both results compared to crayfish in neutral water (pH 7.1) (Ellis and Morris, 1995). This reduced oxygen uptake reduced the extraction of oxygen by the crayfishes tissues. The acidic water hindered the major aerobic and anaerobic pathways in these crayfish compared to those that were in neutral water. The basic water caused such imbalances in the metabolic pathways of crayfish that it caused irreversible damage and may affect their long term survival (Ellis and Morris, 1995). These waters did not effect the amount of energy needed for homeostasis. Since these types of waters affected the respiration and metabolic pathways in the crayfish Cherax destructor, it is likely that waters with extreme pH’s will probably affect most species of crayfish, but this is only a hypothesis.
Thacker et. al. (1993) performed an experiment to study when and why crayfish exhibit the different color morphs and if there are any different behavioral patterns accompanied by these morphs. They used the blue and brown morphs from the species Orconectes virilis for the experiment. Thacker et. al. (1993) found that the blue morph was more active and spent more time in the raised position which may have something to do with their survival rates. They also found that when the crayfish moved from location to location they were able to change their colors to match their environment. This happens over a period of weeks and they can also molt from one color to the next. Another thing that was found was that crayfish have blue and red photoreceptors which collect light from different wavelengths. Crayfish in waters where blue-green wavelengths of light were transmitted were lighter colored and crayfish in water where red wavelengths of light were transmitted were darker colored (Thacker et. al., 1993). Environmental factors, wavelengths of light, diet, water chemistry and genetic differences may all in part be responsible for the color morphs of crayfish (Thacker et. al., 1993).
Crayfish have many predators mainly consisting of different species of fish, but crayfish have become a very popular food for humans also. Crayfish are now commercially cultivated for human consumption or for fish bait. Only ten species are cultured. Crayfish have made many adaptations that allow for successful cultivation (Huner and Lindqvist, 1995). All crayfish can burrow, but this is essential for commercially cultivated ones because their habitats are drained of water for 1-5 months a year. These crayfish are well adapted to utilize aerial respiration which makes transportation of live crayfish to the market easier (Huner and Lindqvist, 1995). All crayfish are able to produce many offspring within one year increasing the numbers available to catch for human consumption and most importantly is that crayfish are resistant to diseases, especially the ones from North America because they are even resistant to the disease caused by the fungus Aphanmyces astaci which is deadly to the European crayfish. American crayfish are also able to live in dirty and polluted water, whereas the European crayfish can only survive in very clean water (Grizimek, 1968).
In conclusion, crayfish are a type of crustacean that can be found in freshwater, brackish and salt water, as well as in burrows. They move by five pairs of legs attached to the thorax and can swim by the six pairs of leg like appendages on the stomach. They are animals with a complex brain. The color of their exoskeleton is determined by a combination of environmental factors, diet, water chemistry, and genetics, and their respiration and metabolic activity is affected by pH within the water..
Barnard, J. L. 1990. Crayfish. In: The World Book Encyclopedia, World Book inc., Chicago, pp.1123.
Ellis, B. A. and S. Morris. 1995. Effects of extreme pH on the physiology of the
Australian ‘yabby’ Cerax destructor: Acute and chronic changes in haemolymph
oxygen levels, oxygen consumption and metabolite levels. Journal of Experimental Biology 198: 409-417.
Encyclopedia Britannica Online A. Accessed October 17, 2000. Crayfish. http://www.eb.com:180/bol/topic?eu=27241&sctn=1.
Encyclopedia Britannica Online A. Accessed October 17, 2000. Excretion.
Encyclopedia Britannica Online A. Accessed October 17, 2000. Stomach.
Stomach. Last updated 2000. Encyclopedia Britannica Online. Available at:
Grzimek, Dr. B. 1968. Grzimek’s Animal Life Encyclopedia. Van Nostrand Reinhold
Company, NY, pp. 487-488.
Huner, J. V. and O. V. Lindqvist. 1995. Physiological adaptations of freshwater crayfishes that permit successful aquacultural enterprises. American Zoologist
Hyman, L. H. 1996. Crayfish. In: Encyclopedia Americana International Edition, Grolier
Incorporated, Danbury, CT, pp.161.
Sandeman, D., R. Sandeman, C. Derby, and M. Schmidt. 1992. Morphology of the brain
of crayfish, crabs, and spiny lobsters: A common nomenclature for homologous
structures. The Biological Bulletin 183: 304-325.
Crayfish. 1995. In: Concise Encyclopedia Biology (T. A. Scott, translator), Walter de
Gruyter Berlin, NY, pp.330.
Thacker, R. W., B. A. Hazlett, L. A. Esman, C. P. Stafford, and T. Keller. 1993. Color
morphs of the crayfish Orconectes virilis. The American Midland Naturalist