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.
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