E-rudd-icated: Tasman cleared of pest fish

Source: NZ Department of Conservation

Date:  21 October 2025

Rudd (Scardinius erythrophthalmus) are an invasive pest fish which threaten our freshwater ecosystems by eating the aquatic plants our native fish species rely on.

The stocky fish has distinctive bright orange fins, and is thought to have been illegally introduced in the Motueka area in the late 1990s for sports fishing. They are known to have been released in 14 ponds.

Between 2000 and 2015, DOC carried out intensive eradication work as part of its local pest fish programme. Now, monitoring has confirmed rudd have been eradicated at all previously known sites.

Helen Otley, DOC Principal Ranger Biodiversity, says it’s been a big effort across the years to get to this point.

“It’s satisfying to confirm they’re gone,” says Helen. “Rudd are fast breeders, and can quickly outnumber and compete with native fish for food, as well as damage water quality.

Adult rudd eat lots of the plants our native fish need to survive, while the juveniles feed on plankton and invertebrates.

“We’re especially grateful to all the landowners who allowed access and helped with the eradication and monitoring work.

“We’re now confident all known rudd populations are finally gone from the region, but it’s always worth keeping an eye out. If anyone sees one in Tasman – they have very distinctive bright orange fins – please call 0800 DOC HOT (0800 362 468) immediately and tell us what you saw, the location, and the water conditions, and provide any photos or videos of the fish.”

Threats like rudd highlight the importance of thorough freshwater biosecurity practices, says Helen.

“Freshwater pests have been spread throughout the country both accidentally and on purpose, and have devastating impacts on our waterways. It’s vital people ‘Check, Clean, Dry’ all clothing, boots, gear, and watercraft when moving between waterways while out naturing.

“To clean your gear spray or soak it using water with 10% detergent. This is especially important right now with the whitebait season underway, and also provides protection against other freshwater pests like didymo, lake snow, and gold clams.

“Our unique nature gives us our identity and way of life, but nature is in trouble. Invasive species put huge pressure on our ecosystems, and we all have a part to play in protecting them.”

Helen says invasive koi carp were also eradicated from the Motueka District in the 2000s, but vigilance is still key due to the devastating impact they could have should they return.

“Unfortunately, we know there are still introduced gambusia, perch, and tench in the area, and we want to prevent them from further spreading and impacting other waterways. Gambusia are a particular concern for whitebait, as they can aggressively attack and prey on whitebait species.

“Recognising the threat that ‘coarse’ fish like rudd and perch pose to the region’s waterways, Fish & Game have prohibited coarse fishing in the Nelson/Marlborough region.”

Background information

For a pest fish to be declared eradicated from a site rigorous monitoring using specific methods must be carried out for three years without any detections.

Rudd are a deep-bodied fish with distinctive bright orange fins. The colour of their scales changes depending on their age, moving from green in juveniles through to a pale orange for adults. They are typically 25cm to 35cm long when full-grown.

For more information about Check, Clean, Dry to prevent spreading freshwater pests:
Check, Clean, Dry: preventing didymo and other pests | NZ Government 

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