Just an interesting article I stumbled across today.
Murdoch University researchers have found some pretty big goldfish and koi living in Perth's waterways.
http://www.news.com.au/national/western-australia/holy-mackerel-goldfish-are-off-the-scale-in-perths-lakes-and-rivers/news-story/f55e2a6be093266fb8d24031456041d8