Signal crayfish

Signal crayfish ( Pacifastacus leniusculus )

The signal crayfish ( Pacifastacus leniusculus Latin ) is a very similar to the noble crayfish from North America derived crayfish, which occurs as neozoon in Europe.

Description

With 12 cm (females ) or 16 cm ( males ) is the signal crayfish slightly smaller than the crayfish. The males are not only larger but also much heavier than the females weighed about 80 g up to 200 g. They also have larger claws. The animals are approximately 7 to 10 years old.

The carapace of the cancer signal is smooth and, in contrast to that of the crayfish no thorns behind the neck furrow. The Rostrumränder appear approximately parallel in the plan as that of the crayfish. The basic color is brown olive with a tendency to. The scissor top is drawn at the joint of the scissors finger with a white- turquoise patch, which also gave the name of the signal crayfish. This " signal spot " but can also be absent or only very indistinctly marked. The bottom of the scissors is red and is used when lifting the scissors as a warning color.

Nutrition

Like most crayfish, the signal crayfish an omnivore, among other aquatic insect larvae, mollusks, and live and dead plant material, eg Eats leaves. Juveniles feed on this most clearly predatory than larger individuals whose gastric contents is often dominated by detritus and plant fragments. In addition, the food depends on supply in the respective waters. At high stocking densities signal crayfish can exert significant predation pressure on preferred prey species and eliminate these from a water body. The foraging usually take place at night, but can also, when the cancer feels safe, be extended to the day. This is especially true when malnutrition.

Propagation

Mating takes place once a year in the autumn from October to November, preferably after a drop in temperature. The eggs and larvae are carried by females later and looked after. Starting in May, but usually only in June / July, the young crabs are independent.

Habitat

The signal crayfish prefers to live in cool streams with slightly alkaline pH ( 7-8) and a higher water hardness ( 10-25 ° GCH ). Because he, unlike the noble crayfish also can withstand higher temperatures, it is also found in standing water as smaller lakes.

In water, the signal crayfish designed its habitat itself: Most caves are dug under rocks or between roots. The animals are not necessarily linked to a cave, sometimes a new cave will be occupied even after a Futtersuchzug.

In a sufficiently large aquarium in the signal crayfish can also be held. An attitude in the garden pond is to be avoided because of the risk of brain drain: The cancer may signal long distances ( up to 2 km ) run across the country to reach another water body. There is also the national legislation considered because an attitude is not allowed anywhere (eg in Switzerland).

The fisheries and conservation laws of most European countries now explicitly prohibit the stocking of signal crayfish in free waters.

Dissemination

Originally, the signal cancer originates west of the Rocky Mountain region of North America. Since 1860 the population of the European lowlands formerly flächenbdeckend occurring, native crayfish was decimated by the massive crayfish plague. To revive the crab fishery then the signal crayfish was first introduced by Sweden, later also from other European countries from 1960 as neozoon. Meanwhile, the signal crayfish has been established in almost all European countries. In Central Europe it is currently the most common non-native Flusskrebsart after the American crayfish.

Displacement of native species

The signal crayfish is resistant to the originating also from North America crayfish plague and brought a new highly virulent strain of the pathogen to Europe. In addition, the signal cancer is more aggressive than native crayfish and, in the case of stone crayfish and clawed crayfish, also significantly larger and produced more offspring. He is superior to the native species thus in direct competition and displaces them completely out of their habitats. Unlike the American crayfish, the signal crayfish also penetrates active before in summer cool waters Headwaters, which has often been offered safe refuge for native crayfish. Expansive signal cancer incidence therefore today represent ( crayfish, stone crayfish and clawed crayfish ) one of the greatest threats to the remainders of the three native to Central Europe crayfish.