Stone moroko
Small invasive freshwater fish from Asia
The stone moroko is a tiny freshwater fish native to East Asia. It has spread across Europe and North America, where it is classified as an invasive species. Authorities restrict its trade and movement to protect local ecosystems from its impact on native fish populations.
- Adults rarely exceed 8 cm in length
- Banned from trade in the European Union since 2016
- Carries parasites harmful to native fish like sunbleaks
- Spread through Europe after introduction in Romania in the 1960s
What it is
The stone moroko, also called the topmouth gudgeon, is a small ray-finned fish. It belongs to the gudgeon family, known scientifically as Gobionidae. Adults are typically between two and seven and a half centimetres long. They rarely grow larger than eight centimetres. This species is native to Asian waters but has established populations in other continents through human introduction.
Where it lives
This fish originates from East Asia, including China, the Korean Peninsula, Taiwan, and the Russian Far East. Genetic studies identify four distinct lineages in its native range. Three of these groups have spread westward into Eurasia. The invasions likely started from the Yangtze River basin, the northern Amur River basin, and the Sungari River basin. In Europe, it entered via Romania in the 1960s and spread through the Danube. It is now found in many European waterways and some lakes in the United Kingdom.
How it lives
Stone morokos feed on the eggs of other fish, which threatens locally valuable native species. They act as carriers for the protist parasite Sphaerothecum destruens. This parasite does not harm the stone moroko but causes high mortality and spawning failure in other fish, such as sunbleaks. The species also brought three monogenean parasites from Asia to Europe. Infections from local generalist parasites are often lower in these invaders, potentially giving them a competitive advantage over native hosts.
Fish and people
Due to its negative impact on ecosystems, the stone moroko is treated as a pest in many regions. In the European Union, it has been on the list of Invasive Alien Species of Union concern since 2016. This status bans its import, breeding, transport, sale, or intentional release. In the United Kingdom, authorities have launched eradication programmes in affected lakes. These efforts involve using the piscicide rotenone to kill the fish and stop their spread.
Status and threats
The species is considered invasive in Europe and North America. Its spread threatens biodiversity by preying on native fish eggs and transmitting deadly parasites. Regulatory bodies actively work to contain its population. The European Union prohibits any commercial activity involving this fish to prevent further environmental damage. Eradication efforts continue in newly discovered populations to protect local aquatic life.
Questions people ask about Stone moroko
How big does a stone moroko get?
These fish are very small. They usually measure between two and seven and a half centimetres. It is rare for an individual to grow larger than eight centimetres in length.
Why is the stone moroko considered invasive?
It eats the eggs of native fish and carries a parasite that kills other species. This disrupts local ecosystems and reduces biodiversity in the waters it invades.
Is it legal to keep stone moroko in the EU?
No. Since 2016, the European Union has banned importing, breeding, transporting, selling, or releasing this species into the environment due to its invasive nature.
Good reading and sources
The facts on this page come from the Wikipedia article "Stone moroko", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.
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