Since the 1960’s signal crayfish has been imported into the Finnish waterways. The signal crayfish endures the crayfish pest well. However, the signal crayfish is able to transmit and spread the disease. The telltale sign that distinguishes signal crayfish from the original Finnish crayfish is the light coloured spot in the claws of signal crayfish. The signal crayfish reaches a length of ten centimetres within three summers, whereas it takes the local Finnish crayfish five to ten summers to reach the same length. Signal crayfish are similar to local Finnish crayfish; they move at night, eat a mostly plant-based diet and live in similar bodies of water. Differences in taste between signal crayfish and the Finnish crayfish have not been found in blind tests. However, there are differences in the edibility, because the shell of the signal crayfish is harder.
The signal crayfish has been declared an invasive alien species throughout the EU. However, it is still possible to catch and sell signal crayfish in Finland during the crayfish season. However, the species may not be grown or spread to new waterways.
