The crayfish, also called crawfish or crawdad, is a freshwater invertebrate that falls in the Kingdom Animalia. They are arthropods that belong to the largest crustacean order, the Decapoda, and are related to the saltwater lobster. This order constitutes the families Astacidae (Northern Hemisphere), Parastacidae, or Austroastracidae (Southern Hemisphere). There are many different genera of the crayfish found all over the world. The most common genera of North America include Procambarus, Orconectes, Faxonella, Cambarus, Cambarellus, and Pacifastacus. The most probable crayfish to be found at Rice Creek would be the Cambarus robustus. Austropotamobius is the most common genus of Europe.
"Crayfish occur in a wide variety of freshwater habitats and are (or were) naturally widespread in all continents of the world except Antarctica and, surprisingly, Africa" (Sutcliffe, 2002, p297). There are more than 500 species of crayfish, more than half of which occur in North America alone. Crayfish are also found in Europe, New Zealand, and East Asia.
These animals are nocturnal so they hide in mud burrows or under rocks and bottom debris during the day and they search for food at night. Their diet at Rice Creek, as well as around the world, includes snails, oligochaetes, small fish; such as minnow, guppies, and goldfish; aquatic insects, aquatic plants, and dead or decaying organisms.
"The crayfish is the largest mobile macroinvertebrate in temperate freshwater ecosystems" (Holdich & Lowery, 1988, p.1). Crayfish are usually 3-4 inches in length. The smallest crayfish, Cambarellus diminutus are about 1 inch long and are found in the southeastern United States. "Astacopsis gouldi on the other hand is one of the largest found in Tasmania which has a length of 40 cm (15 inches) and has a weight of about 3.5 kg (8 pounds)" (Daniel, 2002). The cylindrical-shaped body of the crayfish is covered by a thick exoskeleton, which molts while it grows. There are advantages and disadvantages to having an exoskeleton. The exoskeleton protects the animal from other crayfish and predators like trout and bass, but when it is molted the animal is very vulnerable until the new exoskeleton hardens. Some other predators include eels, pike, chub, perch, herons, mink, otters, snakes, and people.
The crayfish is usually characterized by having a head connected to the thorax, which is called a cephalothorax. The cephalothorax is then connected to the abdomen, which is connected to segmented tail. "The abdomen is approximately thirty percent of the carapace length" (Hobbs, 1987, p.31). The tail can be used to rapidly dart backward if threatened. On the cephalothorax there are two compound eyes, which are attached to movable stalks. These stalks help the animal protect its eyes by retracting them if danger approaches. The crayfish also has a pointy nose and a pair of sensory antennae on its head. There are four pairs of walking legs attached to the thorax. Aside from walking backwards, forwards, and sideways, these legs help the animal probe food in crevices between rocks. Crayfish also have a pair of strong pinchers, which are very helpful in cutting and capturing food, as well as defense. They have five pairs of swimmerets that are located under the abdomen; bailers, which are used to pass water over the gills; and many specialized, food-handling legs. All of the legs on a crayfish can regenerate, or grow back if lost. Crayfish have been known to come in a variety of colors including green, sandy yellow, pink, white or dark brown.
"Crayfish have a life expectancy of about two years and rely on mass reproduction for the continuation of the species"(Daniel, 2002). Crayfish reproduce sexually and mate in fall through winter. A male attracts a female by touching her with his antennae and his claws. He then turns the female on her back, holds her pinchers in his, and then positions his abdomen over hers. He continues to "insert the ischial hooks on his pereiopods into coxal membranes of the pereiopods of the female" (Page, 1985, p.343). This is basically the way in which the crayfish are locked together to mate. After the sperm is in the female, the male places a plug in her so other males won't try to mate with her. When the eggs are fertilized, she glues them to her swimmerets and then finds a safe place to stay. After a few weeks, hatching takes place and the baby crayfish stay with their mom for weeks before going out on their own.
Crayfish are important to the environment and play a very significant role in their ecosystems. Since they are omnivorous, they process organic matter and transform energy between different levels of the food chain. "Their biomass is high in comparison with other consumers"(Holdich & Lowery, 1988, p.128). Most animals cannot readily utilize detritus and living vegetation and so they transfer energy from the producer directly to higher trophic organisms. They are often referred to as "rubbish collectors" because they convert waste into protein.
Over the years, over-fishing, water pollution, irrigation demand, and disease has decreased the population of these important animals. Man is therefore negatively affecting the freshwater ecosystem. There are many efforts being made by conservation biologists and Fish and Wildlife Service ecosystem teams to stop the deduction of crayfish throughout the world.
Bibliography Butler, S.R., DiStefano, R.J., Schuster, G.A. (2003). Crayfish: an overlooked fauna. Endangered Species Bulletin, 28, 2, 10-13.
Daniel, P. (2002). Crayfish Background. Retrieved October 10, 2003, from Hofstra University Web site: http://people.hofstra.edu/faculty/peter_c_daniel/Animal_Physiology/special_topics_spring2002/Ken/Topic_1.html Hobbs, H.H. (1987). A review of the crayfish genus Astacoides (Decopoda: Parastacidae). Wahsington, D.C: Smithsonian Institution Press.
Holdich, D.M.,&Lowery, R.S.(1988). Freshwater crayfish: biology, management, and exploitation. Potland, Oregon: Timber Press.
Page, L.M. (1985). The crayfishes and shrimps (Decapoda) of Illinois. Champaigne, Illinois: University of Illinois Press.
Sutcliffe, D. (2002). Biology of freshwater crayfish. Fisheries Research, 59,1,297-299.