Pseudorasbora parva

The stone moroko (Pseudorasbora parva), also known as the topmouth gudgeon, is a fish belonging to the Cyprinid family, native to Asia, but introduced and now considered an invasive species in Europe and North America. The fish's size is rarely above 8 cm and usually 2 to 7.5 cm long. The fish was introduced in the 1960s into ponds in Nucet, Dâmboviţa County, Romania and it made its way into Danube, then spreading throughout Europe. They pose danger to other species such as the sunbleaks (Leucaspius delineatus). They are the carrier of a parasite (Sphaerothecum destruens) that is not damaging to the topmouth gudgeon, but attacks other fishes like the sunbleaks, which are unable to spawn and have a higher mortality when infected. They also feed on eggs of locally valuable native fish species. The species has also been recently discovered in several lakes in the UK where it is believed to have been illegally stocked.This has called for a large scale eradication programme organised by the Environment Agency who kill the fish off with a piscicide called rotenone.