Photo credit: © Alan Butterworth/Flickr
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Species at a Glance
The Eurasian ruffe is an aggressive member of the perch family that was brought to the United States in the ballast water of ocean-going ships. Its high growth rate, adaptability, and high reproductive success make it a serious threat to commercial and sport fishing.
This small fish has a fairly deep and compressed body reaching 11-15 cm (4.3-5.9 in) in length. The body, which is very slimy when handled, is greenish-brown above, with dark patches on lighter brown sides. The yellowish belly has rows of prominent dark spots on the dorsal and caudal fins. The dorsal fin is made up of a spiny fin and a soft fin that are connected. Sharp spines on their gill covers, dorsal and anal fins make them undesirable to predators. Their head lacks scales and their small downturned mouth resembles a frown.
While it may be confused with native yellow perch (Perca flavescens), the native trout perch (Percopsis omiscomaycus), and the invasive white perch (Morone americana), the Eurasian ruffe can be distinguished by the lack of scales on its head, and its downturned mouth. The yellow perch also has two separate dorsal fins and a body pattern with dark vertical bars, and the trout perch has a short, single-lobed dorsal fin and an adipose fin; these are lacking in the ruffe.
The Eurasian ruffe is highly adaptable and will exploit a wide range of depths and conditions in lakes and rivers. However, it prefers turbid lakes with soft bottoms with little or no vegetation, and rivers with slow moving waters.
Once introduced into Lake Superior, ballast water exchange within the Great Lakes may have facilitated further spread. It may also spread unintentionally through the use of live bait.
Native to fresh and brackish water areas of Eurasia, the ruffe was introduced into Lake Superior in the mid-1980s. Since its introduction, it has spread throughout the upper Great Lakes. It is not currently present in Lake Erie or Pennsylvania waters.
Note: Distribution data for this species may have changed since the publication of Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015), the source of information for this description.
Explosive growth of the Eurasian ruffe population means less food and space in the ecosystem for other fish with similar diets and feeding habits. Because of this, walleye, perch, and a number of small forage fish species are seriously threatened by continued expansion of this pest species.
Information for this species profile comes from Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015).