Common crucian carp (Carassius carassius) used to be one of the most common fish species in the country. It was abundant in outlying ponds, blind branches and ponds around rivers, often remaining the only species in stagnant water due to lack of oxygen and the last species in floating reservoirs or ponds. It is a master of survival in inhospitable conditions where other fish species die during periods of lack of oxygen. It can switch to anaerobic (oxygen-free) metabolism for a long time, and thus survives even in muddy pools covered with ice and snow, where oxygen runs out for a long time in winter.
Although it is generally known that the crucian carp is now on the verge of extinction, its decline, especially in local farm ponds and quarries, is not yet fully mapped. Unlike selected streams and water reservoirs, these waters are usually not monitored at all.
In recent decades, however, our original crucian carp has faced strong competition. The silver crucian carp (Carassius gibelio) was introduced into our waters, which, thanks to its similar resistance and ability to reproduce by means of gynogenesis (a form of asexual reproduction), was able to completely displace the common crucian carp from its habitats, and it also eats other species of animals, such as amphibians. Another danger for common crucian carp is, for example, the invasive eastern minnow (Pseudorasbora parva) or the very intensive use of outlying ponds for fish breeding.

Although it is generally known that the crucian carp is now on the verge of extinction, its decline, especially in local farm ponds and quarries, is not yet fully mapped. Unlike selected streams and water reservoirs, these waters are usually not monitored at all.

Our goal is to find places to focus on saving him.