Crayfish


Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some species are found in brooks and streams, where fresh water is running, while others thrive in swamps, ditches, and paddy fields. Most crayfish cannot tolerate polluted water, although some species, such as Procambarus clarkii, are hardier. Crayfish feed on animals and plants, either living or decomposing, and detritus.
The term "crayfish" is applied to saltwater species [|in some countries].

Terminology

The name "crayfish" comes from the Old French word escrevisse. The word has been modified to "crayfish" by association with "fish". The largely American variant "crawfish" is similarly derived.
Some kinds of crayfish are known locally as lobsters, crawdads, mudbugs, and yabbies. In the Eastern United States, "crayfish" is more common in the north, while "crawdad" is heard more in central and southwestern regions, and "crawfish" farther south, although considerable overlaps exist.
Names used for crayfish in different locations include baybugs, crabfish, craws, crawfish, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, mudbugs, rock lobsters, or yabbies.
The study of crayfish is called astacology.

Anatomy

The body of a decapod crustacean, such as a crab, lobster, or prawn, is made up of twenty body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess two pairs of appendages, although in various groups, these may be reduced or gone. On average, crayfish grow to in length. Walking legs have a small claw at the end.

Diet

Crayfish are opportunistic omnivorous scavengers, with the ability to filter and process mud. In aquaculture ponds using isotope analysis they were shown to build body tissue selectively from the animal protein portion of pelleted food and not the other components of the pellet.

They have the potential to eat most foods, even nutrient poor material such as grass, leaves, and paper, but can be highly selective and need variety to balance their diet. The personalities of the individual crayfish can be a key determinant in the food preference behaviour in aquaria.
Crayfish all over the world can be seen in an ecological role of benthic dwellers, so this is where most of their food is obtained – at the sediment/water interface in ponds, lakes, swamps, or burrows. When the gut contents are analysed, most of the contents is mud: fine particulate organic matter and mixed particles of lignin and cellulose. Some animal material can also be identified, but this only contributes a small portion of the diet by volume.
They feed on submerged vegetable material at times, but their ability to catch large living animal material is restricted. They can feed on interstitial organisms if they can be grasped in the small feeding claws. They can be lured into traps with an array of baits from dog biscuits, fish heads, meat, etc., all of which reinforces the fact that they are generalist feeders.
On a day-to-day basis, they consume what they can acquire in their immediate environment in limited space and time available – detritus. At a microbial level, the FPOM has a high surface area of organic particles and consists of a plethora of substrate and bacteria, fungi, micro-algae, meiofauna, partially decomposed organic material and mucus. This mucus or "slime" is a biofilm and can be felt on the surface of leaves and sticks. Also crayfish have been shown to be coprophagic – eating their own faeces, they also eat their own exuviae and each other. They have even been observed leaving the water to graze.
Detritus or mud is a mixture of dead plankton, organic wastes from the water column, and debris derived from the aquatic and terrestrial environments. Mostly detritus is in the end phase of decomposition and is recognised as black organic mud. The crayfish usually ingest the material in only a few minutes, as distinct from grazing for many hours. The material is mixed with digestive fluids and sorted by size. The finer particles follow a slower and more exacting route through to the hindgut, compared to the coarser material. The coarser material is eliminated first and often reappears in approximately 10 to 12 hours, whereas the finer material is usually eliminated from 16 to 26 hours after ingestion.
All waste products coming out through the hindgut are wrapped in a peritrophic membrane, so they look like a tube. Such an investment in the wrapping of the microbial free faeces in a protein rich membrane is most likely the reason they are coprophagic. Such feeding behaviour based on selection, ingestion, and extreme processing ensures periodic feeding, as distinct from continuous grazing. They tend to eat to satiation and then take many hours to process the material, leaving minimal chance of having more room to ingest other items. Crayfish usually have limited home range and so they rest, digest, and eliminate their waste, most commonly in the same location each day.
Feeding exposes the crayfish to risk of predation, and so feeding behaviour is often rapid and synchronised with feeding processes that reduce such risks – eat, hide, process and eliminate.
Knowledge of the diet of these creatures was considered too complex since the first book ever written in the field of zoology, The Crayfish by T.H. Huxley, where they were described as "detritivores". This is why most researchers have not attempted to understand the diet of freshwater crayfish. The most complex study which matched the structure and function of the whole digestive tract with ingested material was performed in the 1990s by Brett O'Brien on marron, the least aggressive of the larger freshwater crayfish with aquaculture potential, similar to redclaw and yabbies.

Classification and geographical distribution

Crayfish are closely related to lobsters, and together they belong to the infraorder Astacidea. Their phylogeny can be shown in the simplified cladogram below:
Four extant families of crayfish are described, three in the Northern Hemisphere and one in the Southern Hemisphere. The Southern Hemisphere family Parastacidae, with 14 extant genera and two extinct genera, live in South America, Madagascar, and Australasia. They are distinguished by the absence of the first pair of pleopods. Of the other three Northern Hemisphere families, the four genera of the family Astacidae live in western Eurasia and western North America, the 15 genera of the family Cambaridae live in eastern North America, and the single genus of Cambaroididae live in eastern Asia.

North America

The greatest diversity of crayfish species is found in southeastern North America, with over 330 species in 15 genera, all in the family Cambaridae. A further genus of astacid crayfish is found in the Pacific Northwest and the headwaters of some rivers east of the Continental Divide. Many crayfish are also found in lowland areas where the water is abundant in calcium, and oxygen rises from underground springs. Crayfish are also found in some non-coastal wetlands; eight species of crayfish live in Iowa, for example.
In 1983, Louisiana designated the crayfish, commonly called crawfish there, as its official state crustacean. Louisiana produces of crayfish per year with the red swamp and white river crayfish being the main species harvested. Crayfish are a part of Cajun culture dating back hundreds of years. A variety of cottage industries have developed as a result of commercialized crayfish iconography. Their products include crayfish attached to wooden plaques, T-shirts with crayfish logos, and crayfish pendants, earrings, and necklaces made of gold or silver.

Australia

has over 100 species in a dozen genera. It is home to the world's three largest freshwater crayfish:
Many of the better-known Australian crayfish are of the genus Cherax, and include the common yabby, western yabby, and red-claw crayfish.
The marron species C. tenuimanus is critically endangered, while other large Australasian crayfish are threatened or endangered.

New Zealand

In New Zealand, two species of Paranephrops are endemic, and are known by the Māori name kōura.

Other animals

In Australia, New Zealand, and South Africa, the term "crayfish" or "cray" generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania, while the freshwater species are usually called yabbies or Paranephrops, from the indigenous Australian and Māori names for the animal, respectively, or by other names specific to each species. Exceptions include western rock lobster found on the west coast of Australia ; the Tasmanian giant freshwater crayfish found only in Tasmania; and the Murray crayfish found along Australia's Murray River.
In Singapore, the term crayfish typically refers to Thenus orientalis, a seawater crustacean from the slipper lobster family. True crayfish are not native to Singapore, but are commonly found as pets, or as an invasive species in the many water catchment areas, and are alternatively known as freshwater lobsters''.
In the United Kingdom and Ireland, the terms crayfish or crawfish commonly refer to the European spiny lobster, a saltwater species found in much of the East Atlantic and Mediterranean. The only true crayfish species native to the British Isles is the endangered white clawed crayfish.