Tench (Tinca tinca)
A young Tench (Tinca tinca) photo by Piet Spaans
The tench or doctor fish (Tinca tinca) is a freshwater and brackish water fish of the cyprinid (commonly called "carp") family found throughout Eurasia from Western Europe including the British Isles east into Asia as far as the Ob and Yenisei Rivers. It is also found in Lake Baikal. It normally inhabits slow-moving freshwater habitats, particularly lakes and lowland rivers.
The tench is most often found in still waters with a clay or muddy substrate and abundant vegetation. This species is rare in clear waters across stony ground, and is absent altogether from fast-flowing streams. It tolerates water with a low oxygen concentration, even being found in waters where the carp cannot survive.
Tench feed mostly at night on algae and benthic invertebrates of various kinds that they root up from the bottom.
Breeding takes place in shallow water usually among aquatic plants where the sticky green eggs can be deposited. Spawning usually occurs in summer, and as many as three hundred thousand eggs may be produced. Growth is rapid, and fish may reach a weight of 0.11 kg (0.25 lb) within the first year.
Tench have a stocky, carp-like shape, olive-green skin, darker above and almost golden below. The caudal fin is square in shape. The other fins are distinctly rounded in shape. The mouth is rather narrow and provided at each corner with a very small barbel. Maximum size is 70 cm, though most specimens are very much smaller. The eyes are small and red-orange in colour. Sexual dimorphism is weak, limited to the adult females having a more convex ventral profile when compared with males. Males may also possess a very thick and flattened outer ray to the ventral fins.
The tench has very small scales, which are deeply imbedded in a thick skin, making it as slippery as an eel. Folklore has it that this slime cured any sick fish that rubbed against it, and from this belief arose the name doctor fish.
An artificially-bred variety of tench called the golden tench or schlei is a popular ornamental fish for ponds. This form varies in colour from pale gold through to red, and some fish have black or red spots on the flanks and fins. Though somewhat similar to the goldfish, because these fish have such small scales, the golden quality is rather different. This variety is said to have been originally bred in Silesia.
Tench are edible and considered to have a fine flavour, working well in recipes that would otherwise call for carp. They are an important target for coarse anglers and are also used as fodder for predatory species such as bass. Tench, particularly golden tench, are also kept as ornamental fish in ponds and less frequently aquaria.
Large tench may be found in gravel pits or deep, slow-moving waters with a clayey or silty bottom and lots of aquatic vegetation. They take a variety of baits but are "nibblers" and are difficult to hook. Fish over 1 kg (2 lb) in weight are very strong fighters when caught on a rod.