One major threat to fishes as one of the oldest, most numerous in species and certainly the most endangered vertebrates group is, among many others, the introduction of alien species. Alien species are those that have been accidentally or deliberately spread aoutside their natural habitat. Control and prevention of alien species spreading is today one of the most important issues when it comes to protection of nature. Therefore it is very important to consider how and for what reasons have certain alien species of fishes spreaded. In this seminar we will mention all introduced species of freshwater fishes in Croatia, where they came from and and how big is their threat to ecosystems that they inhabit.

Velika prijetnja ribama kao jednoj od najstarijih, vrstama najbrojnijih i zasigurno najugroženijih skupina kralješnjaka je, između ostalih, unos alohtonih vrsta. Alohtone vrste su one koje su se slučajno ili namjerno proširile izvan svog prirodnog areala. Kontrola i sprječavanje širenja alohtonih vrsta danas je jedan od najvažnijih problema kada se radi o zaštiti prirode i stoga je vrlo važno dobro razmotriti načine i uzroke širenja pojedinih vrsta riba. U ovom seminarskom radu ukratko ćemo spomenuti sve alohtone ribe slatkih voda Hrvatske, odakle su došle i kakva je njihova opasnost za ekosustave kojima su se proširile.