For 100 years introductions have been attempted of Europe’s largest freshwater fish. Even now anyone who has caught a Wels here can regard himself as a pioneer.
The Danubian Catfish (Silurus glanis) is a member of a large group of fishes found in the freshwaters of Europe and Asia. The species is also known in this country by its German name Wels, a name which is probably better than the former, for the species is not confined to the River Danube and its tributaries, but occurs over the whole of central and eastern Europe and farther east into western Asia.
It is not native to Britain, where its introduction has been completely artificial, for it is one of the many species which did not reach these islands from continental Europe following the withdrawal of the ice sheets after the last major ice age.
Many attempts at introduction have been made throughout Britain, but few have been successful. Specimens from these successful waters have been used to start new populations, which have maintained themselves. The best known of these introductions was that at Woburn Abbey in the 1880s, providing specimens for other parts of the country.
The Wels, like all members of the Siluridae group, is characterized by a long, sinuous body which is laterally compressed. The head is relatively short, and is slightly compressed on top and below. Also characteristic of the family is the very small dorsal fin, which is situated well forward and has a maximum of only four individual rays.
The anal fin is extremely long, running down more than two-thirds of the body, and is supported by about 90 individual branched rays. There is little space between the anal fin and the relatively small, oval-shaped tail fin. The pelvic fins, also small, are set immediately in front of the anal fin. The pectoral fins are nearly three times as large as the pelvic fins and are set about halfway between the latter and the front of the head.
Common to all catfish, and probably the feature from which they derive their English name, are the barbules found around the mouth, both on the upper and lower jaw. Individual species or groups of species have their own number of barbules. The species of the Wels group, for example, have two very long barbules on the upper lip that extend from near the corners of the mouth. The Wels itself has four extra, much shorter barbules on the underside of the lower jaw, these being evenly spaced in an arc which follows the outline of the jaw. Only two of these short lower barbules are found in the Aristotle Catfish, which is otherwise identical to the Wels.
The long upper barbules are extremely mobile and may be directed forward as well as up, down or sideways. They are used by the Wels as a means of searching for food and to avoid obstacles while swimming, so that they should be considered as feelers rather than barbules. This substitute for sight is clearly necessary, for the species has ex-tremely small, inconspicuous eyes, which are only apparent because of the narrow, bright yellow or golden ring which surrounds the pupil. The fish appears to have a well developed sense of smell, for it displays relatively large nostrils at the base of the long upper barbules or feelers.
Taking into account that all these features are found on all other types of catfishes, it is not surprising that there are many misidentifications.
It is sometimes difficult to distinguish between the different types of catfishes found in this country. These cases involve an entirely separate species which originated in North America and which in most cases finds its way into our waters from aquaria which it has outgrown. This species is a member of the Ictalurus group of catfishes which, in their country of origin, go under various names, including Bullheads, Horned Pout, and Catfish.
The only similarity between this species, or members of the group as a whole, and the Silurid catfishes, is the presence of the barbules or feelers around the mouth. The Ic-talurid catfishes are much shorter than the Wels types, have much larger dorsal fins, much smaller anal fins, and usually two additional short barbules between the long ones on the upper jaw. Even if none of these features can confirm that it is not the Wels the presence of an adipose fin, that is, a fleshy fin without rays, situated between the dorsal and the tail fins, should make it very obvious that the specimen requires more description than the term Catfish, which anglers in this country tend to apply only to Wels. Like the North American species,
Wels the Wels has no scales on any part of its body. Its colouring can vary greatly. The back always has dark blue-black, olive-green or brown tones. These lighten somewhat down the side of the body to give way to white on the belly, although the darker tone of the sides continues over the anal and pelvic fins. The flanks, and often the fins have a marbled appearance produced by irregular patches of colour. Partially or even completely albino specimens are not too uncommon.
The mouth of the Wels is extremely large and is situated across the end of the head. The lower lip protrudes slightly beyond the upper, giving the mouth a shovel-like appearance. It is not equipped with the large teeth associated with predatory fish, having instead a band of small teeth in each jaw.
The number of eggs laid by the species is very high, indicating that the survival rate of the young larvae must be relatively low. Examination of specimens on the Continent, where, in some areas, it is a fairly important food fish, has shown that the female produces about 15,000 eggs per pound of body weight. This occurs on its reaching maturity, at the end of the third or fourth year, when it has attained a length of 2312-2712in and a weight of 2-4lb. The male, which has a slightly faster growth rate, is already mature by the end of the second or third year. Spawning takes place at the end of spring or in early summer, but only if the water temperature exceeds 18°C. If not, it may occur as late as July or August in northern waters such as Britain’s, where such temperatures may not be reached before mid or late summer, if at all. The development of the eggs requires 140-210 day-degrees, that is, 14-21 days at a temperature of 10°C, or 7-11 Vz days at twice the temperature. The high temperature required for spawning, together with the length of development of the eggs in late summer or early autumn, may result in several years passing during which the Wels does not successfully reproduce, so that introductions will perhaps not con- tinue to flourish. Furthermore, even if the eggs do hatch, the larvae may die off because of the lack of food at that time of year.
The yellow, sticky eggs, about 3mm in diameter, are deposited in a ‘nest’ prepared by the parent fish in the shallow, reedy margins of lakes and rivers, or even on flooded marginal meadows. This site, a small area cleared of vegetation, is watched over by the parents for a time with the male often guarding the eggs until they hatch. The newly hatched tadpole-like larvae are about 7mm long and for the first few days of life cling to the vegetation surrounding the nest by means of an adhesive gland. They remain there while they absorb their relatively large yolk-sac, but as soon as this is done they become active swimmers and begin to feed on planktonic animals. Growth can be extremely rapid if the water is a rich one with an abundant supply of this type of food, so that they may reach a length of 1-1 Vfein at the end of four weeks. This growth rate continues, and at the end of the first year they may reach a weight of lib.
Largest freshwater fish
As they grow, the size of their prey increases to take in, besides fish, small aquatic creatures such as amphibians and small mammals like voles, and even small water birds. The Wels must be considered as one of the largest freshwater fish in the world and is certainly the largest freshwater species in Europe. Records of weights indicate that it reaches a length of 7-8ft and a weight of 500lb. Even now, specimens of 200lb are still relatively common and every year sees the capture of several fish of over 100lb by Continental anglers.
The species is relatively shy, frequenting the deeper parts of slow-flowing rivers or stretches of rivers and lakes where vegetation, debris from trees, or even overhanging rock ledges, can provide cover in which they can hide during the daylight hours. Generally, it will only leave its hiding place in search of food at night or during thundery weather on hot summer days, when it moves about close to the bottom. Night fishing, which, unfortunately, is not allowed at most British fishing venues must therefore be considered the most productive approach for the angler.
Much has been written for and against the introduction of this alien species to new waters in this country. While any introduction of alien species, whether fish or mammal, can have disastrous results, as has been shown on numerous occasions, a survey of those waters where the Wels exists indicates that other indigenous species manage to survive extremely well in its presence, as anyone who has fished the Woburn Lakes can verify. There is little chance of Wels taking over a water because our climatic conditions make its reproduction rather unreliable. On the other hand, its potential size and great fighting qualities make it a fine addition to the list of British freshwater species.
There is little doubt that the Wels Catfish is the largest inhabitant of British freshwaters: the 43V&lb record breaker from Wilstone reservoir is a tiddler compared to some fish that have been seen or hooked and lost.
The Cat is sluggish in shape and sluggish by nature; it is in no way built for speed. Largely dependent on the senses of taste, feel and smell, the Catfish is predominantly a scavenger feeding on virtually anything dead, rotting or very slow moving. Dead fish constitute a significant part of the Cat’s diet and so do large freshwater (swan) mussels. The gaping maw of even a smallish Cat is powerful enough to crush a mussel with ease.
The Wels in England is essentially a summer fish and has rarely been caught in water temperatures of less than 65°F. It thrives in hot conditions and appears to be most active in water temperatures between 75 and 85 °F. Although Cats will feed at any time of day or night (they are the most unpredictable of fish) dark, muggy nights with plenty of cloud cover seem the most productive.
In many ways the tactics and tackle for this freshwater leviathan closely resemble those of the big eel specialist. The angler cannot afford to use fine or sophisticated tackle for these giants; brute force and simplicity are essential. The rod needs to be a powerful weapon with a test curve between 2-4 lb, and it is most important that the reel fittings are reliable. A quality fixed-spool reel loaded with at least 100 yards (preferably 200) of line between 12 and 20lb is also essential.
Roach or gudgeon dead bait
Freelining with a dead fish bait is by far the most productive way to tempt a Wels. The preferred fish bait is a smallish roach or gudgeon of 4-5in long, either lip-hooked or with line threaded through the mouth. The hook size is generally a No 2 or 4 and it is important to use a really strong, reliable, sharp hook. Some specialists prefer a bait that is a few days old and ‘off, while others have done equally well with freshly killed baits. Other than fish baits the freshwater mussel must rate as a very close second. Find the largest mussel possible and lightly hook it on the ‘foot’ together with the loose entrails. The use of a wire trace is a matter of personal preference. There have been cases where it was felt that the teeth had ground down a nylon line and eventually caused a break, but generally a line of 12lb b.s. And upwards in good condition should suffice. The landing net needs to be big—at least 3ft in diameter and 4-5ft deep. Pre-baiting with offal, chopped fish or mussels can help.