Crayfish, also called crawfish or crawdad, are closely related to the
lobster. More than half of the more than 500 species occur in North America,
particularly Kentucky (Mammoth Cave) and Louisiana in the Mississippi basin.
Crayfish also live in Europe, New Zealand, East Asia and throughout the
world, including the Tristan da Cunha Islands. Nearly all live in freshwater,
although a few survive in salt water. Crayfish are characterised by a joined
head and thorax, or midsection, and a segmented body, which is sandy yellow,
green, or dark brown in colour. The head has a sharp snout, and the eyes
are on movable stalks. Crayfish are usually about 7.5 cm (3 inches) long.
The crayfish is typical of most shrimplike crustaceans and is characterised
by a joined head and thorax, or midsection, and a segmented body, which
is sandy yellow, green, white, pink or dark brown in colour.
Crayfish are usually about 7.5 cm (3 inches) long. Among the smallest
is the 2.5-centimetre-long Cambarellus diminutus of the south-eastern United
States. Among the largest is Astacopsis gouldi of Tasmania; its length
may reach 40 cm and its weight about 3.5 kg (8 pounds).
The head has two pairs of sensory antennae and a pair of eyes on movable
stalks. The appendages, or pereiopods, of the thorax include four pairs
of walking legs which, as well as walking, are to probe cracks and crevices
between rocks looking for food. Crayfish also own one pair of clawbearing
chelipeds, which it extends in front of its body while moving. These strong
pinchers are specialised for cutting, capturing food, attack, and defence.
A pinch can hurt! The crayfish also has several pairs of specialised food
handling "legs," bailers to cycle water over the gills, and five pairs
of swimmerets which are under the abdomen. All of these "legs" can be regenerated
if broken off.
Crayfish have a hard outside skeleton. This jointed exoskeleton provides
protection and allows movement, but limits growth. As a result, the crayfish
regularly gets too big for its skeleton, sheds it, and grows a new larger
one. This is called molting. and occurs six to ten times during the first
year of rapid growth, but less often during the second year. For a few
days following each molt, crayfish have soft exoskeletons and are more
vulnerable to predators.
Crayfish, common in streams and lakes, often conceal themselves under
rocks or logs. They are most active at night, when they feed largely on
snails, algae, insect larvae, worms, and tadpoles; some eat vegetation
(various water plants). A dead fish worms, corn, and salmon eggs are also
favourites of the crayfish. Studies show that adults (one year old) become
most active at dusk and continue heavy feeding activity until daybreak.
Young crayfish are more likely to be the ones out during bright sunny days,
while the older crayfish are more active on cloudy days and during the
night. General movement is always a slow walk, but if startled, crayfish
use rapid flips of their tail to swim backwards and escape danger.
Most crayfish live short lives, usually less than two years. Therefore,
rapid, high-volume reproduction is important for the continuation of the
species. Many crayfish become sexually mature and mate in the October or
November after they're born, but fertilisation and egg laying usually occur
the following spring. The fertilised eggs are attached to the female' swimmerets
on the underside of her jointed abdomen. There the 10 to 800 eggs change
from dark to translucent as they develop. The egg-carrying female is said
to be "in berry," because the egg mass looks something like a berry. Females
are often seen "in berry" during May or June. The eggs hatch
in 2 to 20 weeks, depending on water temperature. The newly-hatched crayfish
stay attached to their mother until shortly after their second molt.
The natural predators of the Crayfish include
alligators, burbots (a type of cod), chicken turtle, painted turtle, desman
(a type of otter), grackle (a type of a bird).
grackle (a type of a bird).
Crayfish Internal Anatomy
In the open circulatory system blood flows from the heart through the
arteries and returns into open sinuses. The digestive system has a stomach
for grinding food and a gland for chemical processing. The antennal gland
is the main excretory organ.
are part of the order Decapoda constituting the families Astacidae
(Northern Hemisphere), Parastacidae, or Austroastracidae (Southern
Hemisphere). The most common genera of North America include
Procambarus, Orconectes, Faxonella, Cambarus, Cambarellus, and
Pacifastacus. Austropotamobius is the most common genus of Europe. The
genus Astacus occurs in Europe, the genus Cambaroides in East Asia. The
arthopod class also includes centipedes, crustaceans, insects,
millipedes, mites, scorpions and spiders.