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. These exotics include aquatic plants, snails, crustaceans and fish.

Introduced freshwater fish can affect our catchment in much the same way that feral foxes, cats and rabbits cause damage to the landscape. In particular, exotic fish compete with native species for habitat and food.

Many of us are 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.

How do exotic fish affect the environment?

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.

What can you do?

• Choose your aquarium fish carefully: research and ask questions if you are not sure if a fish is suitable or may cause problems
• Keep native species such as western pygmy perch for mosquito control: these species are available from many aquarium stores and should never be collected from the wild
• Design ornamental ponds so fish can’t escape
• Dispose of water from your aquarium on dry land.
• If you catch feral fish while fishing, don’t return them to the water – dispose of them humanely
• Be on the lookout for feral fish: report their presence to FISHWATCH on 1800 815 507 – this helps track infestation and control the problem
• Never release fish from your aquariums or ponds into our rivers, creeks, dams or stormwater drains: even artificial lakes connect to our waterways through drainage networks
• Download our feral fish brochure from the right hand side of this page and educate others about the impacts of releasing aquarium species in our waterways

How to dispose of unwanted fish

• Return unwanted fish to the aquarium dealer from where they were purchased
• Contact local fish societies for advice
• Dispose humanely by putting fish and aquarium water into a plastic bag in the fridge: when the fish stops moving, put the bag in the freezer overnight (recommended by RSPCA WA Inc)

For more information, contact the Swan River Trust 9278 0900 or email info@swanrivertrust.wa.gov.au