Pet aquarium fish are being dumped in rivers where they damage unique local ecosystems by growing up to twenty times their regular size . Goldfish are being caught weighing up to 2kg and koi carp up to 8kg and one metre in length , in the waterways of Western Australia amongst other exotic introduced species . ' A lot of these fish are much larger than the native fish , so they prey on them and compete for habitat , ' Dr David Morgan , the Director of the Centre for Fish and Fisheries Research at Murdoch University , told Daily Mail Australia . Scroll down for video . Goldfish ( pictured ) weighing up to 2kg are some of the exotic aquarium fish invading and destroying WA 's waterways . Koi carp ( pictured ) weighing up to 8kg and up to one metre in length are another of the 13 introduced pests . The native fish in the region , such as this Balston 's Pygmy Perch which has been attacked , are only up 10cm . 'Our native fish are generally less than 10cm in length like the pygmy perch or the native minnows . 'In the south-west of Western Australia 90 per cent of the fish and 100 per cent of the crayfish are only found there , so the rivers are refuges for the native fish and when they are forced to coexist with introduced species , they just do n't do very well . ' Aside from feasting on local fish and taking their homes , introduced species are also bringing exotic parasites and disease with them . 'In Perth we 're aware of a couple of parasites . One is pretty devastating on native fish , it 's an anchor worm which is a little crustacean that leaves a hideous , hideous impact on native fish and was probably introduced by goldfish . A huge Murray River Cod was removed from a Perth wetland in Novemeber last year : ' A lot of these fish are much larger than the native fish , so they prey on them and compete for habitat , ' Dr David Morgan , the Director of the Centre for Fish and Fisheries Research at Murdoch University , said . Pest carps : 'In the south-west of Western Australia 90 per cent of the fish and 100 per cent of the crayfish are only found there , ' he added . 'We 've now found it in three rivers around Perth and south of Perth . 'It 's been only in the last decade that we 've discovered a lot of parasites and disease that we do n't know a lot about - there 's a lot of things that have come in to Australia that we really do n't know anything about . ' Research conducted by Dr Morgan and Stephen Beatty found that at least 13 species of fish had been introduced into south-western Australia , with pet owners believed to be the biggest culprits . In 2012 , the world 's biggest ever specimen of a South American cichlid was found living in WA . 'Goldfish in captivity generally remain orange , grow to about 10-15 cm and weigh less than 100g – in the wild in WA they get to 2KG and 40cm , ' Dr Morgan said . Pet owners who have dumped their aquarium fish in rivers are the culprits behind the invasion . In 2012 , the world 's biggest ever specimen of a South American cichlid ( pictured ) was found living in WA . 'Effectively people are unknowingly doing it - or occasionally they deliberately do it for fish to catch - but they 're basically released by pet owners , so people are n't really aware what damage they 're going to have in the ecosystem , ' Dr Morgan said . 'What you see up and down Western Australia 's coast is a lot of pest fishes are right in town centres and almost every town has one . ' The problem is not unique to Australia . Many countries with Mediterranean climates have also had their waterways invaded by aquarium fish which , due to being extremely easy to breed , take off when in the wild . 'Education is our best solution , once fish get in the waterways they 're extremely difficult to eradicate , ' Dr Morgan , whose organisation euthanizes hundreds of the pests after catching them through electric fishing , said . Introduced species also bring exotic parasites and disease with them . The problem is not unique to Australia . Many countries with Mediterranean climates have also had their waterways invaded by aquarium fish which , due to being extremely easy to breed , take off when in the wild .
Aquarium fish are being dumped in Western Australia rivers by pet owners . Goldfish are growing from the regular 100g to 2kg and koi carp to 8kg . The exotic species compete with 10cm long native fish for food and habitat . They also introduce devastating parasites and diseases onto local species .