Noble crayfish

The noble crayfish Astacus astacus – in Poland called also the river crayfish, broad-clawed crayfish or shoemaker is the largest and most valuable native crayfish species. It can measure up to 20-30 cm in body length and live even 20 years. 
It is a glacial epoch survivor. In those times open waters originated from melting snow and ice. Therefore in present times the most suitable conditions for this species are clean, cool and oxygenated waters, not rich in aquatic vegetation, with hard bottom suitable for burrow. 
Sensitivity of this species makes it a good bioindicator of water cleanliness. The noble crayfish as omnivorous species serves primarily sanitary function in our waters. It feeds on fresh carcass, although a main component of its diet is aquatic vegetation.
The most important feature of this species are massive, not completely closing claws with reddish bottom. Other distinguishing features are small nodules close to cervical groove, flat „cheeks” and distinct ridge of rostrum.
Unfortunately this valuable crustacean is on the edge of extinction in Poland and it is largely the result of human actions. For example, during last 100 years from over 474 known sites of harvesting of this species in the Pomeranian District only about 25 sites still exist.