Native species
Astacus astacus
racul-de-râu
Noble Crayfish
Edelkrebs
écrevisse à pieds rougesracul-de-râuNoble CrayfishEdelkrebsécrevisse à pieds rougesRobust crayfish, medium size, adults often exceeding 10 cm in total length. The dorsal colour of the carapace changes from olive-brown to dark brown depending on several factors (including time since last moulting and age). The ventral side is lighter, tending towards orange-red, whiter in the abdominal region and more intensely coloured at the claw articulations and their ventral surface. The rostrum has more or less parallel and denticulate margins, with a sharp apex. There are two postorbital ridges: the first ends with a spine and the second is blunt. Behind the cervical groove there are several spines. The claws are strong; the propodite has a median cavity flanked by tubercles, and the dactylpodite has a single tubercle in the proximal third.
Native to Central Europe, its range extends from France to southern, central and northern Russia. In the north it occurs in Finland and Sweden, being rare in Norway and Great Britain; in the south it reaches Greece and northern Italy (Souty-Grosset et al. 2006). In Romania its distribution covers almost the entire country, being absent from high mountains and plains. Its range overlaps only marginally with that of the Stone Crayfish (Austropotamobius torrentium). For the distribution map, visit the distribution page.
Males often have longer and stronger claws than females, and the abdomen is visibly broader in females. To precisely distinguish the sexes, especially in juveniles, one should examine the sternal plate and the pleopods. Male crayfish have the first two pairs of pleopods strong and oriented anteriorly (for spermatophore transfer), while in females all pleopods are equal. The shape of the first two male pleopods is also an important criterion for distinguishing it from similar species: the first pleopod (Pl. I) has a distal lobe almost 1/3 of the total length, while the second pleopod (Pl. II) has an exopodite approximately the same length as the endopodite, the distal lobe of the endopodite being approximately 1/5 of its length.
The Noble Crayfish lives in running waters (springs, streams and rivers) or lakes in montane and submontane areas, wherever adequate shelter can be found. It digs galleries in earthen banks or lives hidden among submerged roots; in their absence it shelters under rocks or boulders. It is most active at night, consuming almost any kind of food — a true sanitary of the waters. Adults eat submerged plants when animal food is scarce. It is sensitive to low oxygen concentrations; during very hot summers heavy losses may occur, especially in eutrophic habitats. Natural enemies include the otter, fox, badger and water birds (adults), while fish are the main threat to juveniles — the largest consumer being the European weatherfish (Misgurnus fossilis). A major problem is parasitic disease of viral, bacterial or fungal nature. The oomycete Aphanomyces astaci was introduced to Europe alongside North American crayfish species; native species are extremely vulnerable due to their lack of resistance. Ectoparasitism — by branchiobdellids, chironomids and ostracods among others — is frequent but causes no damage.
Noble Crayfish mate in autumn, in October–November, when females carry white spermatophores on the sternal plate. The clutch contains 90–260 eggs and is carried by the female among the pleopods until the juveniles become independent. Survival rates range from 55 to 90% of the total clutch. Age is estimated from total length as follows: 0+ = 15–23 mm; 1+ = 25–48 mm; 2+ = 50–80 mm; 3+ = 60–80 mm. The growth increment between two moults is approximately 5.0–10.3 mm in males and 2.0–8.6 mm in females. Moulting is more frequent in younger animals (up to 4–5 times per year); adults moult once or twice a year, usually during summer. The few days following a moult are critical: without the protection of the hardened exoskeleton the crayfish can be easily attacked by fish or by other individuals. Lost or damaged appendages regenerate during moult, but a broken claw usually regrows smaller. Sexual maturity is highly variable: males become fertile at approximately 60–70 mm total length and can fertilise eggs every year. Females begin laying eggs at 60–80 mm and may remain sexually inactive for one or more years after a laying.
