Abstract
Huchen or Danube salmon Hucho hucho (Linnaeus 1758) is one of the largest salmonid species in the world and the largest species native to the Danube basin in Europe. In Serbia, this species inhabits the Drina river system, as well as the upper reaches of the River Ibar. It has already been introduced into the rivers Moravica and Đetinja, which are part of the Zapadna Morava catchment area. Most recently, huchen was stocked from its native habitat into the rivers Jerma and Nišava in the Južna Morava river system, and into the River Mlava which flows into the Danube. Huchen is listed as an endangered (EN) species on the IUCN Red List of Threatened Species and is protected in Serbia, and a Conservation Action Plan has already been adopted. In this report, we present the first record of this species in the River Grza, which is a part of the Velika Morava river system, outside its native range. The ichthyofauna of this recipient river consists of brown trout Salmo trutta L. and Eurasian minnow Phoxinus phoxinus L. In a small river of a fragile ecosystem such as this, the introduction of huchen as an apex predator can seriously harm the species of the native fish community, which warns of the illegal stocking measures currently in process.