Rudd (Scardinius erythrophthalmus)
Rudd were first introduced into New Zealand illegally in 1967 when juvenile rudd were ordered into the country through a private consignment. These fish were reared to maturity and bred to produce young.
These young were then introduced into a number of lakes and ponds around the Waikato, where they established populations and spread further. Since then, rudd have been illegally spread around many parts of the North Island. Scattered populations now exist within Canterbury, and one population is in the South Island’s West Coast.
They were originally introduced from their native range of Europe, Russia, and Asia for sport fishing values.
Rudd are designated a Noxious Fish under the Freshwater Fisheries Regulations 1983, everywhere except within the Auckland/Waikato Fish and Game region where they are designated a sports fish (under the Freshwater Fisheries Regulations 1983).
Description and life history
Rudd are quite distinctly different to other fish present in New Zealand; they are quite stocky, deep bodied fish with shiny scales that change colour as they get older. Juveniles tend to be green-silver, while adults tend to be pale orange with a much darker olive-green colour on their back.
Regardless of life-stage, they have very distinctive, bright orange fins. This species of fish can grow up to 35 cm long and weigh around 500 g, but are more commonly found at about 25 cm long.
Rudd live for about 17 years and they spend all that time in freshwater. They mature as young as one year and breed in spring and summer. Eggs are typically found on tree roots and vegetation and only take between a few days to two weeks to hatch.
Rudd can feed on both plants and animals. It is known to hunt smaller fish and invertebrates, while also feeding on aquatic vegetation.
Where are they found?
Populations of rudd can be found throughout the North Island, with Auckland and Waikato being hotspot regions. Scattered populations also exist in the Canterbury region, with one population on the South Island’s West Coast.
Rudd live in ponds, lakes and slow-flowing streams, particularly around areas dense in aquatic plants. They can tolerate poor water quality and low oxygen levels, high salinity. They prefer warm waters but tolerate a wide range of water temperatures.
Why are they bad?
There are several ways in which these fish pose a threat to our freshwater ecosystems:
- Rudd compete with native fish for food habitat.
- Due to their fast breeding, rudd can quickly outnumber native fish in a stream and take over a waterway.
- Once in large numbers, rudd can eat large amounts of native plant species, affecting the populations of these species and degrading water quality.