Ctenopharyngodon idella
The grass carp (*Ctenopharyngodon idella*), popularly known as amur, is a fish native to East Asia, introduced to Romania for controlling excessive aquatic vegetation. It is considered the living "mower" of marshes, with a phenomenal appetite for submerged plants. Due to its extremely rapid growth and vigorous fight on the hook, it has become one of the most appreciated species for sport fishing and commercial aquaculture.
It has an elongated, almost cylindrical body, very robust and muscular. The head is wide, with a terminal mouth lacking barbels. The scales are very large, hard and well outlined by a black margin, giving the fish an "armoured" appearance. Colour varies from golden-green on the back to silver-white on the belly. The fins are large and powerful, adapted for explosive sprints.
Native to the Amur and Yangtze rivers, it has been introduced almost worldwide. In the Danube Delta, it occupies large lake complexes and channels with abundant vegetation. Although an introduced species, it has adapted well, but natural reproduction in the Danube is sporadic, depending on the hydrological regime and temperature.
It is an exclusively herbivorous species at the adult stage. A single specimen can consume daily an amount of vegetation equal to its own weight. It prefers higher aquatic plants (pondweed, hornwort, young reed), which it cuts with the help of strong serrated pharyngeal teeth. It is a cautious fish that often feeds in quiet areas at the edge of reed beds.
The grass carp reaches sexual maturity late, at 6-8 years. Reproduction takes place in the main river current at temperatures above 25°C. The eggs are semi-pelagic and must be carried by the current over long distances so as not to sink into the mud. In Romania, most populations are maintained through artificial stocking from hatcheries, as natural reproduction success is limited.
Globally it is Least Concern (LC). In Romania it is a species of major economic importance. Although useful for vegetation control, its excessive introduction into nature reserves can lead to the destruction of habitats needed by other species through the total elimination of aquatic plants (overgrazing).
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