Silver carp (Hypophthalmichthys molitrix)

There are no self-sustaining populations of silver carp in New Zealand. Like grass carp, silver carp were brought to New Zealand specifically for their potential to control the growth of aquatic plants, in this case tiny floating plants known as phytoplankton. Field trials showed that silver carp could control phytoplankton blooms at most times if enough fish were present. Phytoplankton blooms are undesirable because they cause the water to become de-oxygenated and thus can cause the death of many fish.

Silver carp have a distinctive bright silver colour and are unlikely to be confused with other fish species in New Zealand. They have small scales and no barbels. They feed by filtering phytoplankton from the water using specialised gill structures to do so and their gut is greatly elongated to aid digestion of their food. Like grass carp, silver carp have very specific breeding and rearing requirements and it is unlikely that self-sustaining populations could develop here.

Field trials with silver carp ceased in 1982. Since then brood stock have been transferred to and are maintained at a private hatchery north of Auckland. Silver carp were released into Lake Omapere in Northland in the late 1980’s, but the status of this population is unknown. Their future in New Zealand is uncertain

Silver carp, present only to the left of the barrier, were able to control phytoplankton growth at times in this small lake in Hawkes Bay.