From the Latin introductio - introduction.

Introduction - the relocation by man or accidental introduction of plant or animal species into new habitats.

The introduction of non-native fish species into culture or biocenoses. A distinction is made between naturalization, when a species is transferred to similar or close conditions or biocenoses, its adaptation in this case lies within the potential range and genome capabilities, and acclimatization - with transfer to significantly different conditions, adaptation to which requires a change in the genome structure of the species population.

Introduced species or alien - non-indigenous, non-native to a given territory, deliberately or accidentally introduced to a new place as a result of human activity. In contrast, species indigenous to a given area are called native species.

For example, Rocio octofasciata, an aggressive aquarium fish named after the heavyweight boxer Jack Dempsey, native to Central America, was discovered in a flooded quarry in New South Wales Australia in 2004. Efforts were made to eradicate them, but the fish remained. Jack Dempsey's cichlids are one of about 30 species of fish that have taken root in Australian waters and have a significant impact on its aquatic ecosystems. They emphasize the importance of preventing the importation of invasive fish species because they are extremely difficult or impossible to eradicate once they have taken root in the wild.

Often introduced species can significantly alter the existing ecosystem of a region and cause a significant reduction or even extinction of certain species of local flora and fauna: such introductions are often referred to as biological pollution.