Our fish population consists of indigenous species (i.e. species native to the area), non-indigenous species (i.e. species that have adapted or naturalised) and occasionally observed species.
The group of indigenous species includes the lamprey or lamper eel, the common eel, the riverine brown trout, the marble trout, the lake trout, the grayling or umber, the European bullhead, the freshwater blenny, the burbot, the perch, the goby, the spined loach, the gardon galant, the roach, the chub, the Italian and Mediterranean barbel, the common rudd, the Italian nase, the tench or doctor fish, the vairone, the gudgeon, the bleak, the common minnow, the alosa agone and the northern pike.
The second category includes the common carp, the coregonus or whitefish, the Arctic char, the zander, the common roach, the pumpkinseed, the largemouth bass, the brook trout, the rainbow trout, the lake trout and the crucian carp.
The final group consists of the European sturgeon, the black bullhead, the wels catfish or sheatfish, the Mozambique catfish and the goldfish.
The species in the second and third groups have reached our region via myriad routes. Some have been introduced through “official”, planned releases carried out according to precise, detailed biological knowledge, as in the case of the coregonus or whitefish and the northern pike. Another way is through the deliberate yet unofficial release of such species by individuals who, unaware of the dangers to which they are subjecting local aquatic wildlife, introduce aquarium and/or ornamental fish, such as the goldfish. A case in point, in terms of damage caused, is the rash introduction of the pumpkinseed by a private citizen at the beginning of the twentieth century.
The final kind of introduction is accidental, with non-native species released due to fish from different river basins being used as bait, or fish escaping from farms or recreational fishing facilities, such as in the case of the rainbow trout, the stone moroko (pseudorasbora), the European bitterling and the asp.
The accidental presence of foreign species among fish officially imported to be released must also be considered under this category, examples being specimens of black bullhead hidden among common carp, tench or eels.