Mozambique Tilapia are one of the most invasive animal species in the world fittingly named the cane Toads of the waterways. Tilapia were first introduced in Australia in the 1970’s as ornamental fish. Sadly they have become one of the biggest threats to Australia’s native biodiversity and are now widely spread across South-east Queensland. Biosecurity Queensland states “Historically, the spread of Tilapia has been human assisted by illegal translocations to other waterways, private dams and their use as live bait. Tilapia remains listed as a restricted matter under the Biosecurity Act 2014 to prevent them becoming a commodity. Worldwide they are the 2nd largest farmed fish, but in Queensland you cannot catch one and take it home to eat. Under our laws, Tilapia must be euthanised upon capture and buried above the high tide mark or disposed of in a bin.
Tilapia inhabit muddy bottomed swamps, creeks, lakes and ponds and prefer slow flowing or still water habitats. They are very hardy and can survive temperatures between 8– 42C. However, they prefer temperatures around 16C deg to be active so they can feed. Unlike other fish, they can withstand salinity and low dissolved oxygen. They can grow over 40cm in length and can live up to 13 years. The females protect the eggs and larvae from predators by holding them in their mouths together with the fact that they can reach sexual maturity at small size means they can multiply very successfully. They can even breed in small bodies of water. So it’s no wonder that they have become quite comfortable in Springfield Lakes reaching a considerable size and high density. Because Tilapia are efficient breeders, they can rapidly outnumber native fish and dominate the aquatic environment. They compete for habitat and food, behave aggressively and disturb plant beds when building nests. This also has a severe impact on the survival of native fish.
Currently, there is no single, effective broad-scale tilapia control method and most if not all control methods only remove a small part of the population with each attempt. Given the Tilapia’s very high reproductive rate they will quickly repopulate the area.
The Springfield Lakes Inaugural Pest Fishing Classic was held in March 2018 with the aim of catching the invasive tilapia. The event was a success with approx 250 anglers from far and wide catching a total 900 tilapia weighing over 140kgs. Unfortunately, organised fishing catches only 1% of the Tilapia but it was a worthwhile activity to gauge numbers of native fish and assist in the management of Tilapia numbers in Spring Lake. Electromagnetic fishing will kill approximately 12% of the population but it is very costly and would need to be done regularly to decrease numbers significantly.
How to Stop the Spread of Tilapia and other Noxious Fish.
- Don’t return noxious fish to the water It is illegal to transport Tilapia. If you catch a tilapia you mist kill it humanely and dispose of it appropriately in the nearest bin, ensuring that wildlife cannot remove it. Or bury it above the high tide mark.
- Noxious fish cannot be used as bait.
- Under the Bio-security Act 2014 they cannot be kept, fed, given away or sold or released into the environment without a permit.
- To prevent the spread of tilapia between waterways, check, clean and dry your boats, canoes and gear to ensure there is no weed with tilapia eggs or juveniles attached.
- Don’t dump fish, aquarium contents into the lake as this is possibly how unwanted pets, such as gold fish which turn into carp end up in lakes and creeks.
- If you no longer wish to keep your aquarium fish, please give them to friends or a pet shop.
Written by Judith Vink & Luise Manning