The Stone Moroko, also commonly referred to as Topmouth Gudgeon, is a small-bodied, fast growing, and highly adaptable invasive species of fish in the minnow family. While it can live in a wide variety of freshwater habitat types, it prefers well-vegetated channels, ponds, reservoirs, or small lakes. Adults prefer cool running water and have a broad diet, consisting of small insects, fish, fish eggs, and plant matter.
Stone Moroko is native to eastern Asia, ranging from the Amur, Yangtze, and Yellow River basins of China, the Japanese islands, Taiwan, and western and southern parts of the Korean Peninsula. First recorded in Albania and southern Romania, in a little over 40 years, it has colonized Europe almost entirely, moving rapidly from east to west. Stone Moroko has now established itself in 11 Asian countries, 25 European countries, Fiji, and Algeria. This species can apparently survive in salt water for short periods of time, recovering when back in freshwater. It is therefore suggested that brackish water might be utilized as a dispersal route. There is no documentation of Stone Moroko anywhere in North America, including in Ontario.
Impacts of Stone Moroko
- Invasive populations of Stone Moroko can impact native biodiversity by consuming larger planktonic crustaceans (such as shrimp and small crayfish), which results in increased algae and plant life, decreasing dissolved oxygen needed by aquatic animals.
- They compete with native species for food, spawning, and other habitat resources, which can lead to the loss of these species.
- Stone Moroko can prey directly on juveniles of native fish species.
- This species may also be a vector of several parasites and disease, which can infect native species with impacts on abundance and diversity.
- Stone Moroko is also a documented carrier of the Oriental liver fluke, which is a parasite that infects humans. As such, the Stone Moroko has a potential for high environmental impacts if introduced into the Great Lakes.
How to Identify Stone Moroko
- Stone Moroko are small fish in the minnow family, usually ranging from 2 – 7.5 cm (0.8 – 3 in) in total length, but can reach lengths of up to 11 cm (4.3 in).
- They are characterized by an upturned mouth, which allows them to feed from the surface of the water.
- Stone Moroko have a dorsal (back) fin containing three spines and several soft rays as well as a large caudal (tail) fin.
- Stone Moroko is black or dark grey in colour with lighter shades of grey on their sides and yellow-green to silver on their bellies.
What You Can Do
- Learn how to identify Stone Moroko and how to prevent the introduction or spread of this unwanted species.
- Never buy or keep Stone Moroko. It is against the law to keep a Stone Moroko as a pet, use it as bait, or have a live Stone Moroko in your possession.
- Don’t release any live fish into Ontario lakes or rivers. If you are fishing and incidentally catch a Stone Moroko, you must destroy it. Do not return it to the water.
- If you have any information about the illegal importation, distribution, or sale of Stone Moroko, report it immediately to the MNRF at 1-877-847-7667, toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
- If you’ve seen a Stone Moroko or another invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, visit EDDMapS, or search for the ‘Invasive Species in Ontario’ project on iNaturalist.org to report a sighting.
OFAH/OMNRF Invading Species Awareness Program. (2021). Stone Moroko. Retrieved from: www.invadingspecies.com.
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Header photo by Wikipedia Commons