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  • Rights: University of Waikato. All rights reserved.
    Published 19 March 2014 Referencing Hub media

    Researcher and project manager Erina Watene-Rawiri explains why koi carp are a pest fish.


    We’re trying to get rid of koi carp because they are a pest fish species here. They were introduced back in the 80s, and they cause a lot of damage to our lakes and also the lower Waikato River catchment as a whole.

    The population has exploded, and they now make up 80% of the total biomass in the lower river catchment.

    They contribute to poor water quality, and they also affect the habitat for our native fish and plant species as well.

    Koi carp are bottom feeders that, when they feed, they’re sort of sucking up the bottom, and that dislodges submersed plants. They feed on anything, they feed on fish eggs, they feed on small fish, they feed on whatever is available, and when they’re feeding at the bottom and they’re stirring up the sediment, that causes the clarity in the lakes to reduce. And they burrow away at the banks causing erosion as well, so they contribute to poor water quality in a number of ways.

    Anecdotally, they’ve also been observed feeding on glass eels. Eels are a taonga species for us, and if the koi carp are feeding on the juvenile eels that are heading up into our lakes, then that’s going to have a negative impact there. They’re also competing for food once they’re in the lakes as well.

    Scientists and people in general need to be very careful when introducing new species because they need to understand what the long-term effects may be. They might be able to have a good estimate at what the short-term effects may be, but once they’re released into our natural environment, these species can just take off and create havoc.

    Erina Watane-Rawiri

    Waikato Times

    The Waikato Tainui College for Research and Development acknowledges the financial support given by the Waikato River Cleanup Trust Fund which is administered by the Waikato River Authority.

    The Waikato River Cleanup Trust does not necessarily endorse or support the content of the publication in any way.

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