Fishing methods and gear
Live storage and transport
Killing and cleaning
Freezing and cold storage
Smoked eels for canning
Jellied eels for canning
Chemical composition of eels
This note briefly describes the life history of the eel, methods of catching, storing and transporting it, and the ways in which it can be processed, including freezing, smoking, canning and the preparation of jellied eels.
There are five species of eel in temperate waters and about ten in tropical waters; the one found in Europe has the scientific name Anguilla anguilla and it occurs everywhere in the north-east Atlantic from the North Cape of Norway to the Azores, and in the Baltic and the Mediterranean. It is common in fresh water and estuaries throughout Britain.
Eel, Anguilla anguilla
The eel has an elongated snake-like body, tapering almost to a point at the tail. Although the eel is very slimy and appears to be scaleless, scales are deeply embedded in some parts of the skin. There is a pair of pectoral fins just behind the small head, and there is a small gill opening just in front of each fin. The back fin and the anal fin are very long and merge with the tail fin to form a continuous soft-rayed fin fringe. The eel in fresh water varies in colour from dark brown or olive green to black on the back, and yellowish white to golden yellow on the belly. The yellow gradually changes to silvery white as the eel reaches maturity and prepares to migrate to the sea. Eels are also sometimes described as broadnosed or sharpnosed; the broadnosed eel is one that has excessively developed jaw muscles as a result of voracious feeding, and is almost always a female.
Male eels longer than 0·5m are rarely found; females up to 1m long are common and occasionally they may reach lengths of 1·5m and weights of up to 4kg. Exceptionally large specimens have been recorded weighing up to 8kg. Eels generally range from 0·4 to 0·8m and 0·25 to 1kg in weight.
Eels have been regarded as mysterious creatures since ancient times, and numerous theories have been put forward over the years about how they breed and what their movements are. Their exact life history is still a point of debate among scientists, but the following is a summary of what is now believed to be the most likely sequence of events.
The mature eel spawns at great depths in the Sargasso Sea, midway between Bermuda and Puerto Rico. The eggs, lying near the bottom, hatch into small, transparent, leaf-shaped larvae called leptocephali; at the end of the first summer, when they are about 25mm long, the larvae rise to the surface and are carried by ocean currents on their long migration to the coasts of North America and Europe.
Larvae are carried northwards and eastwards by the Gulf Stream until, about three years after hatching, they reach the coasts of Europe as elvers; at this stage they are about 75mm long and eel-shaped, but with big eyes and an almost transparent body. They move into bays and estuaries and, in late spring, great numbers of them begin the journey upstream; the males are thought to stay mostly in the lower reaches while the females travel much greater distances upstream, moving mainly by night.
Eels remain and grow in fresh water for very long periods, males for about 6-8 years and females 10-13 years; occasionally females have been known to live in fresh water for 25 years or more, probably in land-locked locations from which they cannot escape. Eels in fresh water, known as yellow or brown eels, feed voraciously in summer on worms, small fish, dead fish, molluscs, and other bottom-living animals, and in winter become less active, often lying dormant and half-buried in the muddy bottoms of the waters they frequent.
A female may reach a length of about 0·5m after 7 years in fresh water, but size will depend very much on whether food has been plentiful or not. When the eels approach maturity, they stop feeding and the belly changes colour from yellow to the silver breeding dress, before they start on the long journey back to the Sargasso Sea.
Silver eels move down river in late summer and autumn, mainly by night, and the whole journey to the spawning grounds is thought to take up to a year or more; in winter the eels may hibernate on the seabed in great concentrations en route. It is thought that the eel does not attain full sexual maturity until it reaches the Atlantic a few months before spawning. The female can produce as many as ten million eggs during spawning; it is probable that shortly after spawning, usually early in the year, the eels die. It is thought by some experts that none of the European eels manages to reach the spawning grounds at all, and that the fishery is maintained solely by the return of adult eels from the Americas.
The best time to catch eels is when they are migrating to the sea; they have then reached maximum size, their fat content is high and they are in the best possible condition. Yellow eels of reasonable size, though less valuable than silver ones, are nevertheless readily marketable. Elvers moving upstream are also sometimes captured, either for direct use as food, or to move them safely and quickly to waters otherwise reached by the elvers only after a long and hazardous journey.
The fishery for yellow eels is described first, since this normally involves cheap and fairly simple gear. The capture of migrating silver eels often requires fairly large, robust and expensive pieces of equipment and, for example in many fast-flowing rivers, is sometimes not possible at all.
Yellow eels can be caught by means of baited traps, fyke nets, baited long lines, spears or shore seines. Of these the first three methods are the most useful on a commercial scale; choice of method may, however, be governed by what is permitted by local regulations. Generally speaking, small eel traps and trap nets do not much interfere with other species such as salmon, and conservation often makes it desirable to keep down the number of eels which would otherwise prey upon other species offish.
Many types of portable rigid traps have been used, made from osiers, wood or metal, including converted lobster pots, but one simple design serves the purpose very well.
Simple eel trap
A rectangular cage 900mm by 350mm by 300mm deep is made by stretching 12mm mesh, heavy-gauge wire netting over a framework of stout fencing wire. From one end a tapering funnel of wire netting projects into the cage for a distance of about 250mm. A door large enough to allow a hand to be inserted is fitted in the roof of the cage for baiting the trap and removing the eels. The trap takes about eight hours to make and the materials cost about a pound.
Traps can be set singly, or in fleets of two or more, in any convenient section of river, lake or estuary. Earthworms make good bait and, particularly in estuaries, herring have been found to be successful. The most profitable fishing time appears to be during the first two hours of darkness, especially in estuaries when this coincides with high water. Traps should not be left fishing for much more than two hours as captured eels may escape. This method is most successful in summer, yielding the largest catch about July.
The fyke net is a long, conical net supported by cane or metal hoops with three internal funnels, each with an opening smaller than the preceding one. The first hoop is horse-shoe shaped and the others are circular. Net made from synthetic fibre, such as nylon, is preferable since it has a long life. A wall or wing of net, known as a leader, with headrope and weighted footrope, projects from the middle of the mouth of the cone to guide eels into the net proper. The depth of the leader and the diameter of the mouth are made to suit the water, but up to about 1 m is practicable. The leader and the first two chambers of the cone are of 12mm mesh, and the final chamber of 6mm mesh. All meshes in this Note are measured knot to knot. Although more difficult to make than the baited trap, the materials are not very expensive, particularly if the fisherman can braid his own net.
Fyke net for eels
The net is set, without bait, across the flow of the stream, with the leader close to the bank and the trap furthest away from the bank. It is particularly successful in shallow estuaries in late summer; it is usually set in the evening and the trap end emptied next morning. A number of fyke nets can be set together to intercept eels over a wide area. Fyke nets are of little use in deep or fast-flowing water.
Long lining with baited hooks is possible in fairly still waters such as lakes; the method is used extensively in Lough Neagh in Northern Ireland for example. A typical long line may have anything from 600-1200 baited hooks on snoods up to 2m long, attached at intervals of 1 to 2m along the line. Bait can be earthworm or pieces of freshwater fish. Lines are usually set at night and hauled in the morning; fishing is from late spring to late summer.
Spearing is possible in shallow water when the light is good enough to distinguish the fish lying half buried in the mud or silt, for example in an estuary on a bright sunny day or at night with a bright light. Some designs of spear head permit capture of the eel by gripping it or holding it down without doing much damage, but spearing often wounds or kills the eel and detracts from its marketability. Spearing is illegal in many localities.
The shore seine or draft net can be used in smooth-bottomed, slow-moving water for catching eels. A net up to 90m long and 1·5m deep at the centre is manageable; the wings can be about 3-inch mesh and the long poke or bag of 6mm mesh. The net has to be operated quickly, using a heavy groundrope to maintain close contact with the bottom.
The capture of migrating silver eels in quantity is achieved by means of elaborate and costly weirs and weir nets. In a typical installation, a series of long conical nets is strung partway across a river, often just below the outfall from a lake, with the mouths of the nets facing upstream. The nets may be anything from 9 to 18m long, with conical traps or valves near the small end. Mesh decreases from 65 to 75mm at the entrance to 6mm at the small end. Live boxes are moored near the tails of the nets and permanent staging and gantries may be rigged over the nets to make frequent emptying possible. A permanent wall or fence guides the fish towards the nets, but a small part of the width of the river normally has to be left unobstructed to permit the passage of other fish up and down. The eels begin to move downstream any time after the end of June, and they run mostly at night, particularly during spates when the night is dark and stormy.
Space does not permit further detailed description here of these rather specialised installations, but for fuller details of all kinds of gear for the capture of eels the reader is referred to two other publications:
Capture of Eels Fisheries Notice No. 9, Ministry of Agriculture, Fisheries and Food.
The catching and marketing of eels, W. M. Shearer, Scottish Fisheries Bulletin No. 16, Dec. 1961, pp. 10-12.
Under present marketing arrangements live eels are generally worth much more than dead ones, and considerable efforts are made to keep eels alive after capture. Newly-caught eels are kept in live boxes for up to a fortnight to get rid of any muddy flavour and to clear the guts of any remains of food. The live box is usually a rectangular cage of 12mm wire mesh, kept in the river or in clean, running water; its size will depend on the quantity being handled.
Long-term storage of live eels with only slight loss in condition is practicable for several months in shore tanks, where the water temperature and aeration can be properly controlled. Any eels that die during storage should be removed immediately, gutted and preserved by freezing and cold storage.
Live eels can be transported in small quantities in tray-boxes; large consignments can be shipped in aerated freshwater tanks by road and by sea.
A typical wooden tray-box contains four lift-out trays about 50mm deep, each designed to hold about 10kg of eels graded according to size. The top tray is. usually filled with crushed ice so that cold melt water trickles down through the eels during the journey to keep them cool and lively. The bottom of the box has 50mm upstands at either end inside, so that in effect there are four layers of eels and a layer of ice in each box.
Tray box for live eels
Each tray has drain holes and is divided across the middle to make a total of eight compartments holding about 5kg each, that is about 40kg for the whole box. The lid of the box is nailed on, and the whole is steel-banded both to prevent pilferage and to prevent the eels escaping through the joints. Boxes of this type are used successfully for live transport not only within the UK but also for 24-hour journeys from the Continent with little or no loss. The complete empty box is always soaked in clean fresh water for several days before use. More recently single lidded trays of expanded polystyrene have met with some success on the Continent. Drain holes in the bottom of the box are in raised bosses, so that a shallow pool of water is always left in the bottom to keep the eels moist and cool. The trays can be banded together in a stack and protected against damage if necessary by an outer wooden crate.
Large consignments of live eels from Northern Ireland and to and from the Continent are conveyed in specially built road vehicles or ships. The eels are carred by road in sectional tanks in which the water is continuously pump-circulated and aerated by a compressor throughout the journey; the stowage rate is about one tonne of eels to one tonne of water. For carriage by sea, or for storage at the delivery end, specially built tank craft are used with perforated sides and bottoms, again fitted with water pumps and aeration equipment. The tanks are made of steel with 10mm diameter perforations at 20mm intervals.
The simplest method of killing eels is to put them in a deep container and rouse them with salt; leave them for up to 2 hours to kill them and to remove much of the slime. They should not be completely buried in salt; a good sprinkling is sufficient. They may lose up to 5 per cent in weight during this stage.
Eels are also killed occasionally in the industry by putting them in a tank of fresh water and passing an electric current through the water to stun them, but this method can be dangerous in practice.
Another method of rapidly removing slime sometimes used on the Continent is to immerse the eels in 1 per cent ammonia solution, made by adding one part of ammonia liquor to 100 parts of water.
Newly killed eels should be washed thoroughly in clean water; up to half an hour in cold water, followed by very careful scraping, may be necessary to remove final traces of slime and, where the eels are to be smoked whole, it is necessary to scrub the skin to give a good appearance to the finished product.
Gut the washed eels, taking care to slit the belly 25mm or so beyond the vent in order to remove the kidney; scrub the gut cavity and wash it out carefully to remove all traces of blood from the backbone and throat, and then rinse the eels again. Eels can he gutted satisfactorily in quantity by machine. When hand gutting, sawdust or salt sprinkled on the eels enables the worker to get a firm grip on the fish; sometimes a rough cloth is used or the hands are dipped in dry salt for the same purpose. Weight loss during gutting may be 5-10 per cent. Heads are not removed.
Eels can be frozen and cold-stored satisfactorily in much the same way as for other fish. They should be gutted and cleaned as described and then quick-frozen, either in blocks in a plate freezer or singly in an air blast, and stored at minus 30° C. Eels have a high fat content and should there fore be well protected against rancidity and drying out; the fish should be glazed and then sealed in suitable flexible packaging. Eels should not be frozen ungutted or their normally white flesh will be discoloured by blood. When frozen correctly and stored at minus 30°C, eels should keep in good condition for at least 6 months. For more details on quick freezing and cold storage, see Advisory Notes 27 and 28.
Eels are usually hot-smoked after brining or dry-salting, but the method differs considerably from country to country to suit local preferences; the method given here is applicable to the Torry mechanical kiln and gives a smoked product very similar to those at present imported. This method is most suitable for eels 350 to 700g in weight. Eels less than 350g are too small for most commercial purposes; eels weighing more than 700g will probably require a longer brining time than is given below.
Kill and clean the eels in the manner described, or use thawed eels from properly frozen stock, and then immerse them in 80° brine for 10 minutes; use 275g salt per litre of water. Heavier brining or dry-salting is sometimes used on the Continent, to give a longer shelf life, but lightly salted products are more acceptable to the British taste, and excessive salting results in white spots appearing on the skin of the fish during smoking.
Thread the brined eels on 6mm diameter rods or speats by pushing the pointed end of the rod through the throat from front to back. The rods may be of stainless steel or wood dowelling. Place small lengths of stick between the belly flaps to keep them apart; this allows smoke to penetrate the belly cavity.
The eels are dried, smoked and cooked during the smoking process.
Hang the filled rods in a Torry kiln and smoke the eels for 1 hour at 35°C, 30 mins at 49°C and finally for 1 hour at 77°C. This gradual increase in temperature permits reasonably uniform drying throughout the thickness of the fish; when the temperature is raised too quickly the eels may become case-hardened, particularly when the fat content is low, that is the skin becomes dry and hard but the flesh remains very wet. The eels should lose about 15-20 per cent by weight during the smoking operation.
Remove the eels from the kiln and allow them to cool before packing them; otherwise moulds may form. Brush them lightly with edible oil if necessary and wrap them in transparent plastic film before packing them in boxes.
The finished product is cooked and ready to eat. The flesh should have a good smoky flavour with only a slight taste of salt; the texture should be firm and buttery, but not too tough. The shelf life of the finished product is about 3-4 days at chill temperature.
100kg of fresh, whole eels yield about 60kg of hot-smoked eels.
Kill and clean the eels as described earlier and immerse them in 80° brine for 15 minutes. Thread the eels on rods and hang them in the kiln in the same manner as before. Smoke them for 1 hour at 35C, 1 hour at 49 °C and finally for 1 hour at 77°C. Remove the eels from the kiln, allow them to cool and cut them into pieces the length of the can.
Pack the pieces into the can, fill up with vegetable oil heated to 110°C, and then seal and heat process at 110°C; a 200g oval can takes about 1 hour.
With this method there is very little shrinkage of the meats in the can.
The manufacture of jellied eels is a traditional process about which there is very little authentic information. The advice that follows is based on what is reported to be done by the trade, but the recipes have been tried out on a small scale at Torry.
Kill, gut and clean the eels as described earlier, and cut them into pieces about 40 to 50mm long. Where the eels have been caught by lines it may be advisable at this stage to pass the pieces over a metal detector to make sure that no hooks are embedded in the flesh.
The pieces are next cooked by adding them to boiling water, bringing the water back to the boil, adding about 1kg of salt for every 25kg of eel, and then simmering until the flesh is soft enough to be pushed off the bone with the fingers. Cooking time will vary depending on the size of the eels, the season of the year and the area of capture, and some experience is required to decide when the eels are properly cooked but about 10 minutes actual boiling is typical for yellow eels. Silver eels have a thicker, tougher skin and require somewhat longer, and they should be overcooked rather than undercooked to make the skin soft enough to eat. Next, cold water is added to bring the fat to the surface, and the fat is skimmed off. The cooked pieces and the hot liquor are then poured into large bowls containing gelatine dissolved in a small amount of hot water, usually about a 10 per cent solution, sometimes with a small amount of added vinegar. The amount of gelatine solution needed depends on the condition of the eels and their natural ability to gel; again experience is necessary to get the recipe right. Once the mixture has cooled, the pieces in jelly are packed into cartons for fresh consumption; waxed cardboard, plastics and aluminium foil have all been used successfully as containers. Shelf life can be up to 2 weeks at chill temperature; waxed carton packs may have a shorter shelf life since there is sometimes some reaction between the gelatine and the wax coating.
Another recipe for jellied eels recommends the use of a salt-vinegar solution and a rather longer cooking time as follows:
Water containing 2 per cent vinegar and 3 per cent salt, together with 12·5g of spices per litre, is brought to the boil and 50mm pieces of skinned eel are added. The mixture is brought back to the boil and then left to simmer for about 45 minutes. The pieces are then put in large bowls to cool and a weak gelatine solution is added if there is insufficient natural jelly.
Again a commercial method is given as a guide, the recipe having been tried out on a small scale at Torry.
Pieces of skinned eel are parboiled for about 10 minutes in water containing 2 per cent vinegar, 3 per cent salt, and 12·5g of spices per litre. The cooked pieces are drained, cooled, and then packed either in glass jars or flat cans. The meats are covered with a 10 per cent gelatine solution, 200 bloom strength, containing 1 per cent acetic acid and a few drops of lemon essence. The containers are vacuum sealed and then heat processed at 110°C, 350mb pressure; a 250g pack requires about 30 minutes, a 500g pack about 1 hour. A variation of this procedure is to cover the cooked meats in the container with a spiced vinegar-salt solution before sealing and heat processing.
The fat content of eels varies considerably, but it is
normally higher in silver eels than in yellow eels. Typical composition of the
flesh of a yellow eel is: water 71 per cent, protein 17 per cent and fat 11 per
cent. For silver eels, typical composition is: water 58-60 per cent, protein
14·16 per cent, fat 26-28 per cent. Because of the high fat content, the
calorific value of the flesh of silver eel can be as high as 2570