Catfish - The Introduction


Family:- Siluridae. Catfish:- There are about a dozen members of this family which includes Silurus asotus from Japan, Silurus berdmorei from India and Silurus gilberti from China. However, in Europe the main two groups are wels; Silurus glanis and the Aristotles Catfish (Silurus aristotels). The latter is very similar to the wels, but only possesses two barbules under the lower jaw, whereas the wels has four. The Wels is easily recognized by its huge wide mouth, it has six whiskers, two long ones on the upper jaw, and four smaller ones under its chin. They are also characterised by their long anguilliform bodies and their lack of obvious scales. They have one very small dorsal fin and an elongated anal fin; this stretches for half of the fishes' body. They have a row of small "sand-paper" like teeth on both the top and bottom jaws. Each row consists of hundreds of teeth and these predominantly soft and are used to grip the prey; they slope inwards toward the back of the mouth. In front of the throat cavity are two crushing plates, which the wels use to squash its prey prior to swallowing. They also have a number of short spikes on the edge of the gill rakers. These are used to manipulate their pray prior to swallowing. Although this description might sound horrible it is quite safe to put your hand (and arm) into a catfish's mouth as the teeth are soft and only occasionally scratch. One way to carry the wels is called the "Waller grip", where the thumb is placed on the teeth and the forefinger is placed under the cats jaw for grip.


Species: Silurus glanis; The European Wels Catfish:
Distribution:
The wels is naturally distributed all over Eastern Europe and Asia with high concentrations in the Danube and Volga basins. Through the intervention of man the wels has since found its way into many rivers and lakes in Germany, France, Spain, England and Holland. Silurus glanis has many different pseudonyms. In Holland it is known as "Meerval", in Russia "Ssum", Czechoslovakia "Sumec", Spain "Siluro", Germany "Wels or Waller", and in France "Silure". But In Britain, it is simply referred to as the "Catfish", a name which could apply to many thousands of species world wide and often causes confusion. The catfish is widely distributed, but has a greater concentration in the counties of Bedfordshire, Buckinghamshire, and Cambridgeshire. The wels is not indigenous to this country and they were first introduced into the "Shoulder of Mutton Lake" at Woburn Abbey in Bedfordshire on 27/10/1880. Since then they have been stocked both legally and illegally into many lakes throughout the country. Size: In Russia "Ssum" is frequently caught at 600lb+ by trawlers. In Germany, France and Spain they are caught at over 100 lb with a 100lb cat usually attaining over 6 feet in length. However, in England the record catfish currently stands at 57lb 4oz. Through a study of bones it is thought that a maximum size for this species is around 1,000lb and such specimens are thought to live in some of the big Russian lakes where the commercial trawling vessels cannot fish; the local anglers use baby pigs for bait. In freshwater the catfish's size is only surpassed by that of the white sturgeon (Huso Huso) which may attain weights of 2,200lb, however, the sturgeon is not regarded as a freshwater fish as most of its life is spent at sea. Therefore, Silurus glanis is the largest freshwater fish in the world.
Behaviour:
Catfish are especially suited to the slow-flowing reaches of the larger rivers and lakes especially with dense weed-beds and muddy bottoms. However, catfish are very adaptable and can even be found in the strongest currents of the River Po in Italy where fish up to 200 lb can be seen feeding under boiling water conditions where the current is so strong that boats are unable to anchor. Silurus glanis is mainly a nocturnal scavenger and feeds best in warm weather at night. In the UK they spend many days without feeding and then gorge themselves. On the continent, where the water is warmer, they feed more intensively. Though mainly a scavenger feeding on mussels and crayfish catfish will also feed on live fish that are located by using its long whiskers to feel vibrations given off by injured fish. Diet: The diet of catfish is mainly dead or live fish. However, larger specimens will eat most things including frogs, rats, coypu and snakes. In Russia several specimens have been found with human remains in their guts, although it is thought that the individuals drown first - then are eaten whole. There has never been a reported incident of catfish attacking divers, however, they do attack boats, but this is thought to be a territorial response.
Sexual Differences:
The male has a thin pointed flap of skin behind the vent. In the female this flap of skin is shorter and fatter.


Spawning:
In England spawning takes place from May to July when the water temperature approaches 20°C. The eggs hatch after 3 days dependent on temperature. The larva, which are about 7mm long and have one barbule, feed on plankton, later becoming more predatory and feeding on small fish. The fish grow rapidly and in ideal conditions reach 1lb in weight in the first year. Catfish are also very easy to induce to spawn with the use of hormones. With 5 mg/kg C.P.E or similar, applied to both sexes. In less developed countries wels are just simply left to spawn of their own accord in primitive mud ponds with just wool or rope added as a spawning material. The male fish digs a scrape in the bottom mud and the female then deposits the eggs in a gelatinous lump within the depression. The male then guards the eggs until they hatch.
Commercial Importance:
In Europe, especially in the less developed countries, the wels is an important food fish as its flesh is considered a delicacy. In Germany, France and Spain the catfish is held in less regard and the only commercial interest is for tourism (people travel to fish the large rivers). In England the fish are widely sought after in the fishing fraternity with demand greater then the fish production and consequently the fish sell for a very high price (GBP25 per lb for a single figure fish rising to GBP40 per lb for a 30lb fish). It is illegal to import catfish into this country, except for the aquarium trade, or for use as brood fish.
Conclusion:
Silurus glanis is important in the food industry of certain countries and there is potential for this to be true in the UK. It is possible to rear them on a large scale, but at present, it is difficult to gain a licence to breed them as they are a non-indigenous fish species; the NRA and MAFF are concerned about fish getting into water courses. But there is no evidence to suggest that the wels would be detrimental to the fish stocks in these rivers and every lake and river they have been stocked in to date have been superb fisheries. The wels should be regarded as a scavenger rather then an "active" predator. At present there is a great demand for the species from a fishing point of view because they are a great sporting species and prices can be high. It is illegal to import wels at present to stop spread of disease. They are easy to breed and rear and have an incredible growth rate with the fish reaching a marketable size within two years at which stage they are about 4lb in weight. They will feed on scraps and dead fish and could be reared very cheaply. Such fast growth, and ease of keeping, make it an ideal fish for the food market and in a few years time we might be having wels and chips, instead of the more expensive alternatives. The prices for catfish have dropped dramatically in the last few years, mainly due to imports.

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