Any species that establishes in an area where it does not naturally occur has the potential to become a pest and a serious threat to our native species. Two species of concern that pose a potentially significant threat to NSW waterways are tilapia and didymo.
Tilapia:
Tilapia are listed in the top 100 of the world’s worst introduced fish species. Tilapia is the common name given for fish from Oreochromis spp., Sarotherodon spp., Serranochromis spp. and Tilapia spp., all from the Cichlidae family.
These varieties of tilapia were previously traded in the aquarium industry. They are extremely hardy fish with highly efficient breeding strategies (including mouthbrooding), simple food requirements and flexible habitat preferences.
While there are no existing populations of tilapia in NSW, three species of tilapia, Mozambique mouthbrooder (Oreochromis mossambicus), black mangrove cichlid (Tilapia mariae) and redbelly tilapia (Tilapia zilii) have established successful breeding populations in Queensland, Victoria and Western Australia. These species would pose a significant threat to NSW native fish species if they were to spread to and establish in NSW.
Didymo:
Didymo (Didymosphenia geminata), a freshwater algae more commonly known as ‘rock snot’, is not known to occur in Australia but has established in areas of the northern hemisphere and the South Island of New Zealand.
This highly invasive species can be easily spread by just one drop of affected water. It forms dense brown clumps and can smother aquatic habitats.
Didymo can attach to clothing and shoes, fishing gear or boating equipment. Eradication is virtually impossible once it has become established within a waterbody. Fishers are at risk of accidentally introducing didymo in NSW waters by using contaminated fishing gear and equipment, such as felt-soled waders.
If you have visited an area known to contain didymo, please ensure you check, clean and dry fishing gear and equipment before bringing your gear home.
Pest fish and recreational fishing:
Recreational anglers are often the first to notice new pest species in NSW waterways and can provide valuable information on new incursions of pest fish by reporting new sightings to I&I NSW.
Pest fish, including carp and redfin, can be popular with anglers; however it is recommended that pest fish be humanely dispatched and utilised, and not returned to the water.
Anglers should note that it is illegal to use live bait in NSW freshwater systems and any fish or any part of a fish not native to the waters of NSW (other than dead carp).
Aquatic habitat rehabilitation:
Protection and restoration of aquatic habitats can help to tip the balance in favour of native fish and away from introduced pests such as carp. I&I NSW is involved in several aquatic habitat rehabilitation projects funded by local, state or federal bodies including councils, Catchment Management Authorities, and the Murray-Darling Basin Authority.
Current projects include actions such as replanting riparian (riverbank) areas, returning woody debris (‘snags’) to rivers as fish habitat, and building fish ladders to allow fish to pass in-stream barriers, such as weirs.
Angling clubs, community groups, local councils, Landcare and Rivercare groups and individuals interested in rehabilitating fish habitats throughout NSW can apply for grants. Some grants are made available from the Recreational Fishing Trust using funds generated by recreational fishing licence fees.
For more information on aquatic habitat rehabilitation visit the website and search for ‘habitat management’.
Freshwater weeds:
For information on freshwater weeds in NSW visit the website and search for ‘freshwater weeds’. Help prevent the spread of freshwater pests!
- Don’t keep noxious fish – most noxious fish species are illegal to possess and sell. For the current noxious fish list see the website.
- Don’t return pest fish to the water – if you catch a pest fish dispatch it humanely and utilise or dispose of it appropriately.
- Keep a lookout for suspected pest fish in your local waterways and report suspected new locations (see details at end of publication).
- Don’t transfer fish between waterways, and don’t use live fish as bait in freshwater - it’s illegal!
- Never dump or release fish for any reason, including for recreational fishing, environmental or cultural purposes – this can spread disease and result in a species becoming a pest.
- Obtain a permit to stock fish and buy fingerlings from a registered hatchery to minimise the chances of purchasing juvenile fish contaminated with undesirable species.
- Prevent unwanted hitchhikers – check, clean and dry boats and gear between waterways.
- Design fishponds so that plants, snails, fish or eggs can not escape during heavy rains, and screen all overflow areas.
- It is illegal to buy fish, plants or ‘live rock’ from overseas on the internet; instead purchase them from a reputable local dealer.
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