The Eurasian Ruffe ( pronounced "rough" ) is a small member of the perch family and is native to Europe and Asia where it has become widely distributed. It was first discovered near Duluth in Lake Superior in the mid 1980s, likely as a result of ballast water dumping from ocean-going ships and have since spread to other areas in Lake Superior and Lake Huron. Because of its relatively small size, ruffe have no commercial or sport value.

Characteristics

Ruffe resemble young walleye, yellow perch, and trout perch, but can be distinguished from these by the following characteristics. Ruffe can be identified by their perch-like body shape and are generally less than 20cm (4-6 in) long. They are slimy when handled and have olive brown colouring on the back and pale sides. They have two, large dorsal fins (on top) that are joined together. The row on the first fin has hard spines (11-16 in number) with rows of dark spots and the second fin has soft rays. It has sharp spines on the dorsal and anal fins and sharp spines on its gill covers. It has glassy eyes, a small, down-turned mouth and no scales on the head.

Ruffe have all the characteristics to make it a highly successful invader: it can adapt to many different environmental conditions, will eat a wide range of food, has very few predators, matures quickly and has a high rate of reproduction. The ruffe spends its days in deeper water to avoid predators and moves to the shallows to feed at night. It is found in fresh and brackish water, water with low or high nutrients, in depths of 0.25m to 85m and at a wide range of temperatures. Ruffe mainly feed on aquatic insects and other bottom-dwelling organisms and are know to eat fish eggs. Thus far, only bullheads, yellow perch and northern pike appear to feed on ruffe since their hard spines make it difficult for fish to eat. Ruffe mature young (on average at the age of 2-3) and can spawn in a variety of conditions and habitats. Females can lay between 13,000 to 200,000 eggs per season and have an average life span of 7 years.

Distribution

In the early 1980s, the Eurasian ruffe was discovered in the Duluth Superior Harbour. In 1991, ruffe were reported in the Kaministiquia River at Thunder Bay and are thought to have been transported by ship ballast waters taken from the Duluth Harbour area. Ruffe have spread to numerous locations in rivers and bays around Lake Superior. They have also been found in Lake Huron at Alpena, Michigan. Given time, they could spread to all the Great Lakes and many inland waters. They are now considered the most abundant fish in Duluth Harbour with an estimated number of two million adult fish out of 60 fish species found there (Ruffe Task Force 1992). They are also considered the dominant fish species in the St. Louis River estuary.

 Download the Ruffe distribution map

Impact

Ruffe have a track record and all the characteristics to have the potential to seriously damage our native fish populations. Where they have been introduced to other areas in the world, increasing ruffe numbers have lead to dramatic declines of native fish populations from either direct competition for food or heavy predation of eggs. Ruffe will eat the eggs of native fish species such as whitefish and perch. Ruffe eat a great variety of food which will reduce food sources for many fish species. When the ruffe is not eaten by native predators in significant numbers, or if young predator fish starve because of competition from ruffe before they get big enough to eat ruffe, the result could be an explosion of ruffe and drastic population declines in other species. All these factors: a high reproductive rate; rapid growth rate; lack of predators; ability to thrive in a wide range of conditions and habitats, and its ability to eat almost anything, increases ruffe populations while numbers of native fishes decline. In the areas of the Great Lakes where the ruffe are identified, it has become the most abundant fish species with declines of native fish species such as yellow perch and emerald shiner happening at the same time. It is likely that if ruffe move to or are introduced to the lower Great Lakes, or to inland lakes and rivers, it could have devastating consequences.

Prevention

Once they are introduced into a lake or river, ruffe are almost impossible to control. Therefore, it is vital to prevent their spread to the other Great Lakes and inland waters. Ruffe could be accidentally transported in bait buckets, live wells, and bilge water. Always be careful to never collect baitfish from the Great Lakes for use in inland waters and never take bait from one waterbody and release it into another. Always dump bait buckets on land. Be on the lookout and report possible sightings of Eurasian ruffe.

If you catch a ruffe outside the  area shown on the distribution map, kill it, freeze it or preserve the fish in alcohol and call the Invading Species Hotline at 1-800-563-7711 or contact your local MNR office. Don't throw it back alive!

Under provincial laws, it is illegal to possess a ruffe, dead or alive in Ontario unless transporting a dead one to the MNR. Under U.S. laws, it is illegal to possess a ruffe, dead or alive, in Michigan, Wisconsin and Minnesota.