T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Carp (Chinese grass carp) Ctenopharyngodon idella

Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cypriniformes
Family: Cyprinidae
Subfamily: Leuciscinae
Genus: Ctenopharyngodon
Species: C. idella
Binomial name: Ctenopharyngodon idella
Common name: Grass carp, Chinese grass carp, white amur

Ctenopharyngodon idella is a herbivorous freshwater fish species native to eastern Asia. They are a large fish and often exceed 500 mm in length, 10kg in weight, and can live for 15-20 years. They have no barbels. They are a dark bronze colour fading to a silver colour on the belly. The margins of their large scales are outlined in a darker colour.

Since Ctenopharyngodon idella has very specific breeding requirements and it was unlikely that they would reproduce in New Zealand rivers approval was given by the Government to use them for aquatic weed control. They were introduced to New Zealand in the 1960s. In New Zealand, grass carp are now artificially bred on fish farms licensed by the Ministry for Primary Industries (external site). Each application to use these carp for weed control requires specific authorization.
They eat a wide range of aquatic plants and can be effective for a long period of time over large areas completely eradicate aquatic weeds.

The native sedge Eleocharis sphacelata is threatened by the introduced Chinese grass carp (Ctenopharyngodon idella) which are now established in many North Island waterways. It is very palatable to the grass carp and can be completely eliminated, along with other aquatic plants, from water bodies with heavy carp infestations.

For more detailed information visit: http://www.doc.govt.nz/get-involved/apply-for-permits/interacting-with-freshwater-species/options-for-weed-control/grass-carp/   

A juvenile fish.

Thanks to Wikipedia for text and information http://creativecommons.org/licenses/by-sa/3.0/