Feral Fish

The Swan Canning Catchment supports an array of unique native freshwater fauna. The catchment is home to six of the south-west’s eight endemic freshwater fish species, two of which are rare.

Our native fish populations are now facing a new threat – the introduction and spread of exotic species, including fish. The introduction of non-native, exotic fish species into waterways is a major cause of native extinction and global species decline. Invasive species, including those from other parts of Australia, are now identified as the greatest threat to Australia’s biodiversity after habitat loss.

Many people may be unaware of the problems introduced fish species cause. Small, ornamental fish common in the freshwater aquarium trade cause big problems in our waterways as they flourish, breed and compete with native species. If released, many exotic fish common in the aquarium trade will survive and thrive in our local waterways. They can:

• establish feral populations that compete for food such as crustaceans, insects and plants, or feed directly on native fishes, causing native species to decline
• become aggressively territorial, reducing available habitat for native fish and other water dwelling animals, and exhibit aggressive behaviours – such as fin nipping – that can seriously injure or kill native fish
• introduce parasites and spread disease that may affect native fish and other freshwater animal life; and
• alter habitats by digging in riverbeds, uprooting plants and muddying the river: this can increase the level of nutrients in the water and may lead to excessive algae growth

It should be noted that most aquarium fish are hardy and have wide environmental tolerances. Pearl cichlids [ 104 kB ] are an example of a ‘freshwater’ aquarium fish that can tolerate salinities equivalent to seawater and a wide range of temperatures. They therefore have the potential to spread widely in the Riverpark.

Other feral fish species that occur in the Swan Canning Riverpark include:

• Goldfish (Carassius auratus)
• Koi Carp (Cyprinus carpio)
• Mosquito fish (Gambusia holbrookii)
• Silver Perch (Bidyanus bidyanus)
• Spangled Perch (Leiopotherapon unicolour)
• Redfin Perch (Perca fluviatilis)

Once established in our waterways, feral populations of introduced fish are notoriously hard to eradicate. These populations often result from intentional translocations or introductions. Educating the public about the consequences of such introductions and the connectivity of waterways is therefore often the primary management tool.

Managing Feral Fish

The Swan River Trust is working with the Department of Fisheries and local government authorities to manage feral fish in the waterways of the Swan Canning Riverpark.