Abstract
<jats:p>While introduced fish initially had a positive impact on the socio-economic aspects of society, they have recently threatened the biodiversity of native fish in Indonesia. Preventive efforts are needed by inventorying introduced fish traded in Medan Regency, as the origin of the entry of alien fish in North Sumatra, Indonesia. This research used a survey method conducted at 30 ornamental fish markets in the Medan Regency area from March to May 2024. The authors classified introduced fish based on conservation status, natural distribution zone, year of introduction, and invasive threats based on various databases and journals. Fish Invasiveness Screening Test (FIST) analysis was also carried out to assess the risk level of the introduced fish. The results of the analysis show that there are 55 introduced fish species traded in Medan Regency, which are classified into 46 genera, 29 families, and 14 orders. The orders Cichliformes and Cypriniformes had the highest numbers of species, followed by Characiformes, Siluriformes, Osteoglossiformes, Anabantiformes, Cyprinodontiformes, and others. There are 13 species of introduced fish that should be prohibited from circulation because they threaten aquatic ecology, including Amphilophus citrinellus, A. labiatus, Cichla ocellaris, C. piquiti, Lepisosteus oculatus, L. osseus, Lates niloticus, Melanochromis auratus, Pterygoplichthys multiradiatus, P. pardalis, Pygocentrus nattereri, Semaprochilodus insignis, and Tetraodon duboisi. The results of the FIST analysis show that 21 species of fish represent a high risk of threat to aquatic ecosystems, followed by 13 species at moderate risk, and 21 species at low risk.</jats:p>