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Life in Freshwater

White-clawed Crayfish ( Austropotamobius pallipes )

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Crayfish side view

These lobster-like creatures are very distinct as the front pincers (called chelae) are greatly enlarged. However, they are not aggressive and the pincers cause no harm if handled. The general colour is a light brown or green. The total length of an adult is around 12 cm. The first two pairs of abdominal limbs are modified in the male and are very different from the rest of the legs. In the female they are all the same and are used to carry the eggs. There are around 6 species of crayfish which can be found in Europe.

The White-clawed Crayfish is the species native to Britain and Lowland, Central Europe but has been on the decline due mainly to a fungal disease, Aphanomyces astaci. The crayfish inhabits weedy rivers where the water is clear. They prefer hard water such as chalk rivers. Several species have been introduced to Europe from North America for food and these are becoming more abundant than the native species as they are unaffected by the fungus, e.g. Oronectes limosus is found throughout except for north Scandinavia and Britain, Pacifastacus lenuisculus is in Scandinavia and Central Europe.

Crayfish have been hunted for human food for centuries and this coupled with the fungal disease, Aphanomyces astaci, has caused a considerable drop in the species density and distribution around Europe.

ECOLOGY: By day the crayfish hides amongst weed such as crowfoot which may form dense banks of material in the middle of flowing rivers. Large stones, holes or large debris may also protect them. They emerge at night to feed on suitable animal material, dead or alive. The diet is very diverse from insect larvae, worms and even other crayfish. Plant material may also feature. Crayfish are not just favoured by humans but are a key dietary item of otter and freshwater birds. Pairing takes place in the autumn when the male sprays the gametes on to the female where it sticks to her underside. She then lays the eggs which stick to the legs. From this position the sperm fertilises the eggs. They hatch in the spring to form a tiny crayfish which may continue for some while to remain attached to the female.












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