The stone moroko (''Pseudorasbora parva''), also known as the topmouth gudgeon, is a species of freshwater

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

belonging to the

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Gobionidae Gobioninae is a monophyletic family of Eurasian cyprinoid fishes. This is a species rich clade which, as a subfamily of the Cyprinidae was divided into five tribes: Gobionini, Pseudogobionini, Hemibarbini, Coreiini, and Sarcocheilichthyini. T ...

, the gudgeons. This species is native to

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

, but introduced and now considered an

invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. The fish's size is rarely above 8 cm and usually long. Pseudorasbora parva mouth

Invasive species

In Europe, ''P. parva'' is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union. The fish was introduced in the 1960s into ponds in Nucet,

Dâmbovița County Dâmbovița County (; also spelt Dîmbovița) is a county () of Romania, in Muntenia, with the capital city at Târgoviște, the most important economic, political, administrative and cultural center of the county. It is a traditional administra ...

Romania Romania is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to ...

and it made its way into

Danube The Danube ( ; see also #Names and etymology, other names) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest sou ...

, then spreading throughout Europe. These fish feed on eggs of locally valuable native fish species. Four phylogenetic lineages of ''Pesudorasbora parva'' were identified within its native range, and three of them contributed to the dispersal within more western regions of Eurasia. One of these lineages was initially distributed in the north of China and the Far East of Russia, the second one was in southern China, the third one was in the Korean Peninsula and, probably, in the adjacent regions of China, and the fourth in Taiwan. Geographical distribution of ''COI'' lineages suggests three donor regions of stone moroko invasions into more western regions of Eurasia: the basin of the

Yangtze The Yangtze or Yangzi ( or ) is the longest river in Eurasia and the third-longest in the world. It rises at Jari Hill in the Tanggula Mountains of the Tibetan Plateau and flows including Dam Qu River the longest source of the Yangtze, i ...

River, the northern (Russian) part of the

Amur The Amur River () or Heilong River ( zh, s=黑龙江) is a perennial river in Northeast Asia, forming the natural border between the Russian Far East and Northeast China (historically the Outer Manchuria, Outer and Inner Manchuria). The Amur ...

River basin, and the

Sungari The Songhua or Sunghwa River (also Haixi or Xingal, ''Sungari'') is one of the primary rivers of China, and the longest tributary of the Amur. It flows about from Changbai Mountains on the China–North Korea border through China's northea ...

River basin (right tributary of the Amur in the territory of China). 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 Rotenone is an odorless, colorless, crystalline isoflavone. It occurs naturally in the seeds and stems of several plants, such as the jicama vine, and in the roots of several other members of the Fabaceae. It was the first-described member of the ...

Parasites

''Pseudorasbora parva'' poses danger to other species such as the sunbleaks ('' Leucaspius delineatus''). These fish are the carrier of a parasite, the protist '' 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. A 2023 study showed co-introduction of three

monogenea Monogeneans, members of the class Monogenea, are a group of ectoparasitic flatworms commonly found on the skin, gills, or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they ...

n species, '' Dactylogyrus squameus'', ''Bivaginogyrus obscurus'', and '' Gyrodactylus pseudorasborae'' into Europe along with their fish host from East Asia. In addition to co-introduced parasites, the fish was infected with a local generalist, the monogenean ''Gyrodactylus prostae''. Monogenean infections were generally lower in non-native host fish, potentially giving an advantage to this invading species.

References

{{Taxonbar, from=Q583540 Pseudorasbora Taxa named by Coenraad Jacob Temminck Taxa named by Hermann Schlegel Fish described in 1846