Common name:Grass carp
Scientific name:Ctenopharyngodon idella
Alternative common names:
The grass carp is an herbivorous, freshwater fish species with an elongated, chubby, torpedo-shaped body. This species occurs in lakes, ponds, pools and the backwaters of large rivers, preferring large, slow-flowing or standing water bodies with vegetation.
Where does this species come from?Eastern Asia, from the Amur River in eastern Russia to the West River in southern China.
What is its invasive status in South Africa?NEMBA Category 1b in national parks, provincial reserves, mountain catchment areas and forestry reserves declared in terms of the Protected Areas Act. NEMBA Category 2 for breeding of grass carp. NEMBA Category 3 in all other discrete catchment systems in which it occurs.
Where in South Africa is it a problem?uMngeni River in KwaZulu-Natal and Mpumalanga.
How does it spread?It spreads via the authorised and unauthorised stocking of grass carp that has taken place for biological control of vegetation. It was introduced into South Africa from Malaysia and Germany between the years of 1967 and 1975.
Why is it a problem?In large numbers, grass carp can remove all aquatic vegetation from a body of water. When this happens, valuable habitat for fish is lost, which can cause fish population imbalances. The loss of all vegetation also reduces the food base for fish, as some aquatic invertebrates rely on aquatic vegetation. Some waterfowl rely on aquatic plants, so an overabundant grass carp population that eliminates all plants can impact waterfowl. Grass carp can also affect water quality. They may carry exotic parasites or diseases that could be transmitted to indigenous fish.
What does it look like?Description: The grass carp grows rapidly and young fish stocked in spring at 20cm can reach 45cm by autumn. Adults often attain nearly 1.2m in length and over 18kg in weight. There are three simple and seven branched rays on the dorsal fin. They are silvery to olive in colour. Habitat: Grass carp prefer the shallow, abundantly vegetated waters of lakes, ponds and the backwaters of large rivers. They require riverine environments with long reaches, high water volume, turbulent flow and warm water temperatures to successfully reproduce. They can tolerate a wide range of water temperatures (near freezing during winter and near 37°C during summer), low oxygen levels and brackish water. Breeding: Grass carp prefer to spawn in large rivers instead of lakes or slower-moving water (however, they have the potential to breed in slower-moving water if need be). This is potentially dangerous as larger rivers flow through many areas, which furthers the invasion.