Class:Crustacea
Order:Decapoda
Family:Astacidae
The European crayfish (Austropotamobius pallipes, Lereboullet 1858) is a small freshwater crustacean belonging to the Astacidae family. In Italy, the species Austropotamobius italicus (Faxon, 1914) is present, which in turn is divided into four subspecies: Austropotambius italicus carinthiacus in central and north-western Italy, Austropotambius italicus carsicus in the north-east, Austropotambius italicus italicus in the Tuscan-Emilian Apennines, and Austropotambius italicus meridionalis in central-southern Italy and Friuli Venezia Giulia. Their presence is a very reliable indicator of the health and integrity of the environment.
In many European countries, it is nicknamed “white-footed crayfish” due to the characteristic colouring of its limbs and belly, in contrast to the rest of its body, which ranges from reddish brown to dark green, sometimes with lighter shades closer to yellowish. It has a particularly stocky body and a robust carapace; it can reach 11–12 cm in length and 90 g in weight. Males are larger than females.
Feeding and Habits
The crayfish is basically a solitary animal with more pronounced territorial tendencies in males, especially during the breeding season, which also increases the propensity for movement in both sexes. It is particularly aggressive in defending its territory and in sexual fights, as demonstrated by the capture of specimens with partially or totally mutilated limbs or claws.
They have markedly crepuscular and light-shunning habits, although they cannot be defined as strictly nocturnal. They are found in clear, well-oxygenated and moderately cold flowing waters, typical of small mountain and hill streams, as well as in the upper reaches of large rivers. They can also be found in lakes, provided these receive a constant supply of fresh water.
Being a cold-blooded organism, it prefers cool waters with an optimum temperature of around 15 °C and a range that varies by a few degrees, tolerating a maximum temperature of 23 °C.
It is omnivorous: the crayfish feeds on all kinds of animal prey (aquatic insect larvae, small benthic crustaceans, molluscs, annelids, amphibians and their larvae, small fish), as well as plant debris, aquatic plant leaves and fruit that has fallen into the water. Young shrimp tend to be zoophagous, while adults are generally detritivorous. Cases of cannibalism are also not uncommon.
Social behaviour and relations with humans
Mating takes place in autumn, when the water temperature drops; it is preceded by a rather complex courtship ritual, at the end of which the male grabs the female with his claws and turns her onto her back, attaching himself to her thorax and fertilising her.
The female carries the fertilised eggs (which can number between 30 and 100) on her abdomen for 5-6 months, taking care of them, ventilating and cleaning them continuously. In spring, they hatch, but the small larvae remain attached to their mother’s body for some time.
Crayfish must constantly escape from numerous predators who, like humans, appreciate their flesh. In particular, the larvae are often preyed upon by other large hunting larvae, such as those of beetles that feed in water, such as ditiscids, or dragonflies, which are also particularly voracious in their larval stage and can even prey on small shrimp. Among the fish, trout, sunfish, perch, eel and chub are worth mentioning. Crows and many wading birds also feed on these crayfish.
The species is considered endangered according to the criteria of the IUCN Red List. The factors that most threaten its survival in Italy are:
- the presence of exotic (i.e. non-native) crustaceans introduced by human activities, in particular those that have escaped from farms and compete for resources and introduce diseases unknown to the native species and therefore much less tolerated.
- organic pollution, which reduces the oxygen content in the water, making it impossible for the crayfish to survive
- inorganic pollution, mainly due to heavy metals contained in fungicides.
- crayfish fishing, which, although prohibited, is not completely stopped. Overfishing of the species results in the so-called “bottleneck effect”, i.e. a decrease in genetic diversity in a population following a drastic reduction in the number of individuals, which means that the Italian subspecies Austropotamobius pallipes italicus is at high risk of extinction and has not been found in many areas.
In addition to the factors listed above, there is also a dangerous fragmentation of the range and populations, which could lead to genetic weakening and rapid extinction in Italy.
