Temporal range: MesozoicRecent
koura, Paranephrops planifrons (Parastacidae)
Crayfish, also known as crawfish, crawdads, freshwater lobsters,
mountain lobsters, or mudbugs, are freshwater crustaceans resembling
small lobsters, to which they are related; 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 there is running fresh water, while others thrive
in swamps, ditches, and rice paddies. Most crayfish cannot tolerate
polluted water, although some species such as Procambarus clarkii
are hardier. Crayfish feed on living and dead animals and plants.
The name "crayfish" comes from the Old French word
escrevisse (Modern French écrevisse). The word has been modified
to "crayfish" by association with "fish" (folk
etymology). The largely American variant "crawfish" is
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"
further south, although there are considerable overlaps.
The study of crayfish is called astacology.
In Australia (on the eastern seaboard), 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 yabby or
koura, from the indigenous Australian and Maori names for the animal
respectively, or by other names specific to each species. Exceptions
include western rock lobster (of the Palinuridae family) found on
the west coast of Australia; the Tasmanian giant freshwater crayfish
(from the Parastacidae family) found only in Tasmania; and the Murray
crayfish found on 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 (Cherax quadricarinatus) in the many water
catchment areas, and are alternatively known as freshwater lobsters.
The body of a decapod crustacean, such as a crab, lobster, or
prawn (shrimp), is made up of twenty body segments grouped into
two main body parts, the cephalothorax and the abdomen. Each segment
may possess one pair of appendages, although in various groups these
may be reduced or missing. On average, crayfish grow to 17.5 centimetres
(6.9 in) in length, but some grow larger. Walking legs have a small
claw at the end.
Geographical distribution and classification
The three families of crayfish
Parastacidae: Cherax pulcher.
There are three families of crayfish, two in the Northern Hemisphere
and one in the Southern Hemisphere. The Southern Hemisphere (Gondwana-distributed)
family Parastacidae lives in South America, Madagascar and Australasia,
and is distinguished by the lack of the first pair of pleopods.
Of the other two families, members of the Astacidae live in western
Eurasia and western North America and members of the family Cambaridae
live in eastern Asia and eastern North America.
Madagascar has an endemic genus, Astacoides, containing seven
Europe is home to seven species of crayfish in the genera Astacus
Cambaroides is native to Japan and eastern mainland Asia.
The greatest diversity of crayfish species is found in southeastern
North America, with over 330 species in nine 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
Crayfish were introduced purposely into a few Arizona reservoirs
and other bodies of water decades ago, primarily as a food source
for sport fish. They have since dispersed beyond those original
Australia has over 100 species in a dozen genera. In Australia,
many of the better-known crayfish are of the genus Cherax, and include
the marron from Western Australia (now believed to be two species,
Cherax tenuimanus and C. cainii), red-claw crayfish (Cherax quadricarinatus),
common yabby (Cherax destructor) and western yabby (Cherax preissii).
The marron are some of the largest crayfish in the world. They grow
up to several pounds in size. C. tenuimanus is critically endangered,
while other large Australasian crayfish are threatened or endangered.
Australia is home to the world's two largest freshwater crayfish
the Tasmanian giant freshwater crayfish Astacopsis gouldi,
which can achieve a mass of over 5 kilograms (11 lb) and is found
in rivers of northern Tasmania, and the Murray crayfish Euastacus
armatus, which can reach 2 kilograms (4.4 lb) and is found in much
of the southern Murray-Darling basin.
In New Zealand, two species of Paranephrops are endemic, and are
known by the Maori name koura.
Fossil records of crayfish older than 30 million years are rare,
but fossilised burrows have been found from strata as old as the
late Palaeozoic or early Mesozoic. The oldest records of the Parastacidae
are in Australia, and are 115 million years old.
Some crayfish suffer from a disease called crayfish plague,
caused by the North American water mould Aphanomyces astaci which
was transmitted to Europe when North American species of crayfish
were introduced there. Species of the genus Astacus are particularly
susceptible to infection, allowing the plague-coevolved signal crayfish
to invade parts of Europe.
Crayfish are eaten worldwide. Like other edible crustaceans,
only a small portion of the body of a crayfish is eaten. In most
prepared dishes, such as soups, bisques and étouffées,
only the tail portion is served. At crawfish boils or other meals
where the entire body of the crayfish is presented, other portions,
such as the claw meat, may be eaten. Like all crustaceans, crayfish
are not kosher because they are aquatic animals that do not have
both fins and scales. They are therefore not eaten by observant
As of 2005, Louisiana supplies 95% of the crayfish harvested
in the US. In 1987, Louisiana produced 90% of the crayfish harvested
in the world, 70% of which were consumed locally. In 2007, the Louisiana
crawfish harvest was about 54,800 tons, almost all of it from aquaculture.
About 70%80% of crayfish produced in Louisiana are Procambarus
clarkii (red swamp crawfish), with the remaining 20%30% being
Procambarus zonangulus (white river crawfish).
Crayfish are commonly sold and used as bait, either live or with
only the tail meat, and are good at attracting channel catfish,
walleye, trout, largemouth bass, smallmouth bass, pike and muskellunge.
Sometimes the claws are removed so that the crayfish do not stop
fish from biting the hook. Crayfish easily fall off the hook, so
casting should be slow.
The result of using crayfish as bait has led to various ecological
problems at times. According to a report prepared by Illinois State
University, on the Fox River and Des Plaines River watershed, "The
rusty crayfish (used as bait) has been dumped into the water and
its survivors outcompete the native clearwater crayfish". This
situation has been repeated elsewhere, as the crayfish bait eliminates
The use of crayfish as bait has been cited as one of the ways
zebra mussels have spread to different waterways, as members of
this invasive species are known to attach themselves to crayfish.
in a freshwater aquarium
Crayfish are kept as pets in freshwater aquariums. Crayfish
kept as pets in the US from local waters are usually kept with bluegill
or bass, rather than goldfish or tropical or subtropical fish. They
prefer foods like shrimp pellets or various vegetables, but will
also eat tropical fish food, regular fish food, algae wafers, and
small fish that can be captured with their claws. They will sometimes
consume their old exoskeleton after it has moulted. Their disposition
towards eating almost anything will also cause them to explore the
edibility of aquarium plants in a fish tank. However, most species
of dwarf crayfish, such as Cambarellus patzcuarensis, will not destructively
dig or eat live aquarium plants. They are also relatively non-aggressive
and can be kept safely with dwarf shrimp. Because of their very
small size of 1.5 inches (38 mm) or less, some fish are often a
threat to the crayfish.
Since crayfish are accustomed to being in ponds or rivers, they
will have a tendency to shift gravel around on the bottom of the
tank, creating mounds or trenches to emulate a burrow. Crayfish
will often try to climb out of the tank, especially if an opening
exists at the top that they can fit through.
In some nations, such as the United Kingdom, United States,
Australia, and New Zealand, imported alien crayfish are a danger
to local rivers. The three species commonly imported to Europe from
the Americas are Orconectes limosus, Pacifastacus leniusculus and
Procambarus clarkii. Crayfish may spread into different bodies of
water because specimens captured for pets in one river are often
released into a different catchment. There is a potential for ecological
damage when crayfish are introduced into non-native bodies of water
(e.g., crayfish plague in Europe).
Crayfish have been recorded as an invasive species from Louisiana
to Europe to China. They have been known to consume local rice crops