The wels catfish – also called the catfish wels, catfish or wels – cannot be mistaken for any other fish in British waters (except the burbot which is probably now extinct in Britain). It has a long tapering body, a large head and dull, mottled skin. Colours vary, but generally it has a dark grey back with pale brown flanks and a whitish belly.
Follow the feeding
Wels are predatory fish and, like most predators, spend their early life feeding on invertebrates. As they grow, they start to feed mainly on fish. They are noted as nocturnal predators, though many have been caught in daylight. As with all species of catfish (which is only a term for fish, both freshwater and marine, which have ‘whiskery’ features), wels are mostly active near the bottom, so other bottom dwellers such as tench are a particular favourite, as are the larger freshwater shellfish. They also sometimes feed higher in the water, coming to the surface to take wildfowl and – according to myth – the occasional dog and even sheep. Wels have huge jaws, so there is no problem about being able to gulp down a small hound in one mouthful.
These catfish were introduced to Britain relatively recently – the late 19th century -and so have not reached anything like their maximum size. They are also adapted to warmer weather than is usual in Britain, so it is highly unlikely that British wels will ever grow large enough to worry pets or livestock.
A nesting fish
Wels do best in still waters and large, slow-flowing rivers. In Britain they are confined to a few reservoirs, lakes, gravel pits and canals in the South East and Midlands but they are slowly spreading as a result of both legal and illegal stocking.
The wels is one of the rare freshwater fish which forms a crude nest for the protection of its eggs. The male hollows out a small depression in the bottom and often partly lines it with vegetation. Spawning takes place when the water temperature is high enough – about 19°C (66°F) – usually between May and July in a warm summer. The female sheds a sticky pile of up to half a million eggs into the nest. These are guarded by the male until after they hatch.
Obviously the vast majority of the fry must die during the first few months -probably over winter – otherwise any water would quickly become overrun.
After about three weeks the eggs hatch and the male loses interest in his offspring, except perhaps as a tasty snack. The young fish take between three and five years to mature, at which point they can weigh anything from 2-10 lb (0.9-4.5kg). In England, wels reach weights of around 20-30 lb (9-13.6kg) in ten to fifteen years. At this weight they usually stop growing even though they can live for much longer than this. It seems British waters are too cold, or perhaps the prey species too small, to encourage growth to the huge proportions of Eastern European fish.