In Western Australia feral fishes are found mainly in waterways in the vicinity of major urban areas. These introduced freshwater fishes include Goldfish (Carassius auratus); Koi Carp (Cyprinus carpio); Rainbow Trout (Oncorhynchus mykiss); Brown Trout (Salmo trutta); Eastern Mosquitofish (Gambusia holbrooki), One-spot Livebearer (Phalloceros caudimaculatus); Guppy (Poecilia reticulata); Swordtail (Xiphophorus helleri); Redfin Perch (Perca fluviatilis); Mozambique Mouthbrooder (Oreochromis mossambicus); and Eastern Australian Silver Perch (Bidyanus bidyanus).
Feral fishes are a threat to unique native freshwater fishes because they can tolerate degraded habitats, are highly adaptable and reproduce readily. Feral fishes are: predators of native freshwater fishes; compete with native fishes for food decrease water quality; and introduce parasitic diseases, such as anchor worm. They are a significant threat to native freshwater fishes in the south-west of Western Australia, where 82% of fishes are unique local species and 55% of species are endangered.