Native species — Endemic
Austropotamobius bihariensis
racul bihorean
Idle Crayfish
Leerkrebs
écrevisses au reposracul bihoreanIdle CrayfishLeerkrebsécrevisses au reposThe species was first described in 2019 based on molecular and morphological evidences. Small to medium sized crayfish, rarely reaching 10 cm in total length. The carapace is smooth; the dorsal colour is brown, the ventral side being brighter and tending towards creamy-white, yellowish-orange on the ventral surface of the claws. The rostrum is triangular with concave sides (bell-shaped), with a discrete median carina and a short apex. There is one postorbital ridge, without spine. The cervical groove is smooth. The most important feature distinguishing it from the Stone Crayfish is the absence of denticulation on the ventral edge of the antennal scale. The claws are robust, with fewer and larger tubercles compared to its relative, the Stone Crayfish.
Endemic to Romania, its range is strictly limited to the western Apuseni Mountains. The species most likely originated from north of the Dinarides; following a tectonic displacement at the beginning of the Miocene (ca. 15 m.y.a.), populations were isolated and eventually reached their present position. For approximately 11 m.y.a. the species was completely isolated due to the evolution of the Pannonian Basin. Currently it inhabits the tributaries of the Criș rivers. Abundant populations have been found in tributaries of Crișul Negru and Crișul Repede. For the distribution map, visit the distribution page.
Males often have longer and stronger claws than females, and the abdomen is 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 an important criterion for distinguishing it from similar species: the first pleopod (Pl. I) has a distal lobe almost 1/2 of the total length, while the second pleopod (Pl. II) has an exopodite no longer than 2/3 of the endopodite length, the distal lobe of the endopodite being approximately 1/2 of its length.
Being recently described, the Idle Crayfish is not yet listed by specific conservation legislation. It currently benefits from the "strictly protected" status of its relative, the Stone Crayfish. The Idle Crayfish prefers small to medium rivers and streams; it may occasionally reach subterranean waters during floods. It typically digs galleries in earthen banks but is frequently found under submerged roots, rocks or boulders. Mostly nocturnal, it is omnivorous: juveniles are predominantly carnivorous (insect larvae) while adults consume mainly plant material, including fallen leaves. Highly sensitive to oxygen deficiency and chemical pollutants. The main threats are stream channelisation and urbanisation of submontane areas. Natural predators include fox, wolf, bear and badger (adults) and fish (juveniles). The spread of North American crayfish species represents a major threat as vectors of Aphanomyces astaci, the crayfish plague oomycete. Ectosymbionts of the group Branchiobdella are frequently found on the carapace but do not cause damage.
Mating occurs in autumn, at the end of October, before the waters freeze. During this period white spermatophores can be observed on the sternal plate of the female. The clutch contains 40 to 70 eggs (up to 100 reported) and is carried by the female among the pleopods until the juveniles become independent. For appropriate embryonic development water temperature should not exceed 5°C. Juvenile survival rates range from 10 to 70% of the total clutch. Moulting is more frequent in young animals (up to 4–5 times per year); adults moult at most twice a year, usually between May and September. 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 appendages can regenerate during moult but usually reappear smaller. Sexual maturity is reached at 3–5 years, at a total length of 35–50 mm. Males can fertilise eggs every year while females may remain sexually inactive for one or more years after a laying.
Holotype (male) and paratype specimens (male and female) were collected from Damiș, Bihor County, Romania. They were donated by the author to the „Grigore Antipa" National Museum of Natural History: holotype voucher number DCP829, paratypes voucher numbers DCP830 and DCP831. (see letter of acknowledgement) 
