There are two types of "tolstolob", in Russian "белый" и "пестрый", соответственно:
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.

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Species Summary for Aristichthys nobilis
Bighead carp

Aristichthys nobilis (Richardson, 1845)
Family: Cyprinidae (Minnows or carps)
Order: Cypriniformes
Class: Actinopterygii (ray-finned fishes)
FB name: Bighead carp
Distribution: Asia: China. Introduced to numerous countries and has achieved a near global distribution. However, its breeding requirements are very specialized and stocks are maintained by artificial reproduction or continuous importation. Several countries report adverse ecological impact after introduction.
Biology: Occurs in rivers and lakes. Feeds mainly on zooplankton. Bottom feeding fish (Ref. 6459). Marketed fresh and frozen.
Max. size: 100.0 cm TL; max.weight: 20 kg
Environment: benthopelagic; freshwater ; depth range - 5 m
Climate: temperate; 4 - 20°C; 64°n - 18°s
Importance: fisheries: highly commercial; aquaculture: commercial; aquarium: show aquarium
Threatened: Not in IUCN Red List () , (Ref. 36508)
Dangerous: potential pest

К сожалению, копърка не нашел.