Mud-loving Tench Tinca tinca

There is something very satisfying about the appearance of the deep-bodied tench. It is a member of the carp family and can vary in colour from almost black through green to pale yellow. The most usual colouring is a deep olive-green back and flanks, with a paler belly. There is also an ornamental golden variety, which sometimes has black patches on its back and sides.

Tench feed almost exclusively on the bottom - finding their food by rooting around in the mud. As they do this they often release strings of fine bubbles. These come from pockets of marsh gas (mainly methane) disturbed by the fish as they feed in the mud. The gas filters through the tench's mouth and gills, and the fine gill rakers produce characteristic pinhead bubbles,

Tench eat all the small prey animals found on the bottom but are especially fond of bloodworms, jokers and other insect larvae. They also eat larger items such as worms, snails, mussels and even some small fish. They feed mainly at dawn and dusk, but sometimes continue through the day or night, depending on the venue. In winter they hardly feed at all, lying inactive on the mud for long periods.

More and more very large tench are being caught in Britain. There have been several theories to explain this. Perhaps the most likely is that as more and more farm fertilizer has leaked from the land into the water, so waters have become much weedier and richer in invertebrate life. As this forms the largest part of the tench's diet, the fish has started to grow even larger,

Though some tench are found in quite fast-flowing rivers such as the Trent, they thrive best in rich still waters, sluggish rivers and canals. You won't find them in very fast water or poor upland lakes, but they are highly tolerant of low levels of dissolved oxygen, and so do well in shallow ponds, which have low water levels, or even become stagnant, in summer.

Tench won't spawn unless the water has remained at 18°C (64°F) or above for at least two weeks. They therefore spawn later than most other British coarse fish - between May and August. Each pair takes several weeks to spawn, leaving many clusters of pale green eggs stuck to the stems of water plants. Large females carry as many as 750,000 eggs.

The eggs hatch out in four or five days but the larvae remain stuck to the plants by their heads until the yolk sac attached to their bellies is used up. Then the fry must forage for food. The young fish live in the weeds and are very rarely seen or caught, though large numbers of them die in the first year, probably during the winter,

Growth is very slow at first - they only reach 20-30cm (8-12in) after three years, and spawn for the first time after at least four. In ideal conditions, they reach about 2,3-2.7kg (5-6lb) after ten years and can live up to twice that age.

Tench slime was thought to have magical medical properties - other fish would deliberately rub against them and be cured of all ills.

In the Middle Ages tench slime was believed to cure headaches, toothaches, jaundice and many other illnesses.

People also believed that pike would not eat tench, perhaps because of their mythical powers. Those anglers who have felt the frustration of losing tench at the net to pike know this just isn't true.

Sywell Reservoir, Northamptonshire This 100 acre water yields many 3.2kg (7lb) fish and some of 3.6-4.1 kg (8-9lb).

Wilstone Reservoir, Tring, Hertfordshire Few fish but they reach over 5.4kg (12lb)

Blenheim Lakes, Oxfordshire Lots of good sized fish.

T.C. Pits, Oxfordshire Used to produce fish over 3.6kg (8lb) and there are still some big specimens.

Bradley's Lake, South Cerney, Gloucestershire Fabulous (and large) gravel pit for quality tench.

Johnson's Lakes, Kent Big fish up to 4.5kg (10lb).

Yately Lakes, Leisure Sport, Hampshire These waters hold many big fish.

Weight: up to 6.8-7.3kg (15-16lb); average 1.4kg (3lb)

Length: 60-66cm (24-26in)

Life-span: 20 years

Favourite waters: Still waters, particularly shallow ponds and lakes

• Tench are covered in tiny scales which are well embedded in the skin and covered with a thick layer of slime.

• The small eyes have red irises. The upper lip is larger than the lower - a help to the bottom feeding tench. There are two tiny barbels at the corners of the mouth.

• All the fins are large and rounded. The males have longer pelvic fins than females and this can be used to tell the sexes apart. On males the fins reach back as far as the anal vent.

• The tail is very slightly concave. The 'wrist' of the tail is extremely thick.

The British tench record is 6.548kg (14lb 7oz), taken by Gordon Beaven in September 1993 from a private gravel pit.

Until the 1970s, the specimen weight for tench was about 2.3kg (5lb) and a tench of 3.2kg (7lb) was the fish of a lifetime. But now, partly due to advanced fishing methods and the fact that fish may be getting bigger, the specimen weight is now about 3.2kg (7lb).

On still waters such as lakes and ponds the sight of tiny bubbles fizzing on the surface usually means that the tench are about and feeding.

Tench feed in the black silt around the bottom of reed mace beds. They remove snails and snail eggs from the stems of Norfolk reeds and dig out small freshwater mussels from the edges of gravel bars. They also patrol the silt between the gravel bars, sometimes stopping to feed in the mud.