Introduced Fish

The Basin already contains at least 11 introduced fish species in the wild, some in pest proportions, and further introductions are inevitable over time. Both the abundance and attributes of some introduced fish continue to cause damage to habitats and populations of native species. Most attention has been given to carp and trout because they are the largest and visibly most abundant, but there are many other species that can have impacts through predation, competition and disease. The risk of further introductions into the Basin— especially from aquariums and nearby rivers outside the Basin—also needs to be considered. Precautionary approaches, to minimise the risk of future introductions, and pest management principles, to address existing introductions, should be applied across the Basin.

The focus of all management of introduced fish species needs to be on reducing the impacts of such fish on native species, rather than on complete eradication of numbers. The best approach to reducing such impacts is an integrated one that combines a range of techniques. For example, with carp, appropriate techniques could include rehabilitating the wetting and drying cycles for floodplain wetlands, commercial exploitation, release of the carp herpes virus, and the installation of screens and fish traps to prevent adult fish migrations. There is unlikely to be one ‘silver bullet’ that can solve any single introduced species problem. Control of alien species needs to be part of an overall river rehabilitation process.