The tench, of the genus Tinca and also known as doctor fish, is a common freshwater fish that can be found throughout the waters of Europe and Western Asia. It is generally found in central Europe, although several large populations have been found as far west as Great Britain and as far east as Central Russia. In some areas Tench are fished for food, in others the fish is classified as a nuisance. They live on the bottoms of lakes and the dirt and sediment they stir up can suffocate eggs of other species.
The tench is a member of the Cyprinidae family, which makes it a close genetic relative to the common carp. Similar to their carp cousins, they generally have a short, broad body, small eyes, and a narrow mouth framed by whiskers, much like a dogfish or catfish. The main difference between the tench and the carp, however, is that the former can survive in poorly oxygenated conditions, while the latter cannot. Tench are usually green in color, although the hue of their skin can vary from one end of the body to the other. Its skin is typically quite thick, studded with tiny scales, and slimy, much like that of an eel. They normally never grow very far beyond 25 inches (65 centimeters) and 10 to 12 pounds (4.5 to 5.4 kilograms), and even that is an unusually large size for them to achieve.
Tench are mainly found in relatively stagnant freshwater habitats, such as lakes or slow-moving rivers. The carnivorous fish feed almost exclusively on algae and various small animals that take up residence in the mud, though in the wintertime it stays in the mud and doesn't eat. They breed in shallow water among aquatic plants where their eggs can be deposited. As a result, still waters are the perfect environments for them to thrive in, due to the abundance of vegetation and the conditions which allow algae and mud to accumulate without being swept away by fast-flowing streams. A female fish can lay up to 600,000 eggs every year; in comparison, a salmon lays about 2,500 eggs per year and a carp can lay more than a million.
Because of their abundance and similarity to carp, tench are often used primarily for cooking or as bait for larger predatory fish. However, there are certain albino members of the species, known as golden tench, which are occasionally used to populate ornamental fish ponds because of their highly visible bright orange colors.