There’s Something Fishy Going On: Impacts of Introduced Fish Species

Theres Something Fishy Going On

The movement of plants and animals from one habitat to another is fundamental to the survival of species and maintenance of healthy biodiversity. The importance of movement is even greater in highly dynamic ecosystems such as rivers, where natural cycles of wetting and drying create shifting habitat conditions. Destruction of linked habitats is likely to be one of the significant drivers of damage to river ecosystems, but invasive species can also have significant negative impacts. Conservation of waterways, in particular control and management of invasive fish species, is a vital component of the Corridors for Climate Change Project.

Within the Northern Agricultural Region (NAR), one of the most critical introduced invasive fish species negatively affecting our river systems is the Mozambique tilapia (Oreochromis mossambicus). Mozambique tilapia are included on IUCN’s 100 worst invasive species list. Unfortunately, this species is currently found in the Chapman River, and due to their breeding behaviours have the potential to establish in other rivers. Tilapia are mouth brooders and eggs can survive in the freezer or on a dry riverbank. This is why tilapia must never be thrown back into the water or put into crab pots or crayfish traps as bait.

Tilapia are hardy fish, tolerating a wide range of temperatures and capable of surviving in a variety of harsh conditions. They usually live in mud bottomed, well-vegetated waters, and are often seen in small schools. Tilapia have a highly successful breeding strategy (up to 1,200 eggs a year, in up to four broods) and low juvenile mortality. After spawning the female takes the eggs in her mouth, where they hatch. The fry then remain in their mother’s mouth for up to 14 days before they are released, and may remain near the mother and re-enter her mouth when threatened until about three weeks old, thus receiving protection from predators.

Impacts from tilapia include:

  • Habitat damage through nest-building activities, increased water turbidity, uprooting of aquatic vegetation, altered erosion patterns, and increased bank instability.
  • Aggressive behaviour towards native fish, which disrupts the breeding success of native fish.
  • Introduction of new types of pathogens and parasites. These infectious agents can be harmful to the health of native fish that have not previously been exposed to them.

There is currently no overall option for the control of tilapia, with the main focus of management being restricting their range of movement by attempting to minimise spreading caused by people. This includes not releasing unwanted aquatic pets, not transferring aquatic creatures between waterways (including bait), humanely dispatching of any captured pest species and disposing of them away from the water, as well as reporting suspected pest fish sightings to WA Pest Watch.

Targeted education campaigns actively highlight the potential damage caused by introduced tilapia to the natural environment and educate the public about what the fish look like and what to do if one is found. An easy way to distinguish pest fish from native species is by looking at the dorsal fin (the fin that runs down the fish’s back). Most pest fish have a single or continuous dorsal fin whilst most native species have two fins or at least a distinct notch between the front (spiny) half and rear (softer) portion of the dorsal.

NACC’s Corridors for Climate Change Project aims to increase community awareness about the impacts of tilapia, and to collaborate with other organisations to control and manage invasive fish species in our river systems.

For more information about current research project into tilapia in the NAR please visit:

For more information about NACC projects into restoration of vegetation along rivers, creeks and wetlands please visit:
Source: Corridors for Climate Change

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