Fish
Grass Carp
Ctenopharyngodon idella · also called white amur
A canal choked with dense aquatic weeds is stocked with a handful of grass carp, and within a season the waterway runs clear again, each fish having eaten its way through a genuinely startling amount of plant material every single day.
Overview
The grass carp, Ctenopharyngodon idella, is a large herbivorous fish native to East Asia and now introduced to freshwater habitat across much of the world. Its enormous appetite for aquatic vegetation has made it a deliberately deployed tool for weed control, managed carefully through sterile stocking to avoid the species becoming a problem of its own.
An appetite turned into a management tool
Rather than simply being a fish that happens to eat plants, the grass carp has become something closer to living infrastructure, introduced specifically because its hunger for vegetation solves a maintenance problem that would otherwise require considerably more effort to manage by other means.
Status
Least Concern — widespread within its native East Asian range and across many regions where it has been introduced for vegetation control.
Grass Carp: common questions
How much can a grass carp eat in a day?
A grass carp is capable of consuming a substantial portion of its own body weight in aquatic vegetation each day, an enormous appetite for plant material that makes the species genuinely effective at reducing excessive weed growth in lakes, ponds, and canals where it has been deliberately introduced.
Why are sterile grass carp used for vegetation control?
In many regions, grass carp are stocked as sterile triploid individuals specifically so that the fish can provide the desired aquatic vegetation control without being able to reproduce and spread uncontrollably into surrounding waterways, balancing a useful management tool against the ecological risk of an unchecked invasive population.
Is the grass carp related to the silver carp?
Yes, the grass carp is closely related to other introduced Asian carp species such as the silver carp and bighead carp, though it differs from those relatives by feeding almost entirely on aquatic plants rather than on plankton filtered from open water.
Where does the grass carp live?
The grass carp is native to large river systems in East Asia, and it has since been introduced to freshwater lakes, ponds, and canals across much of the world specifically for its usefulness in controlling excessive aquatic vegetation.