European eel breeding and aquaculture

European eel is a valuable fish that has exceptionally tasty meat. In nature, the population of the European eel is greatly undermined and therefore the eel is actively grown in aquaculture. Let's look at how eels are reared in artificial conditions, how to organize the cultivation of eels in a pond or in a pool or cages, and how to grow eels in a farm to marketable size. We will also consider where the eel lives and many other questions.

Content

• Description of the European river eel
• What kind of fish is the European eel?
• Where does the European eel live?
• Where is the eel fish found?
• Where are eels found in Russia?
• Habitat of the European eel
• How do eels reproduce in nature?
• Advantages and disadvantages of European eel when growing
• What does a European eel look like?
• What does eel eat?
• How fast does an eel grow?
• Obtaining juvenile river eel
• Growing river eel to commercial fish
• Stocking density of river eel
• Commercial sizes of European eel
• Fish productivity when growing eel in a pond
• Intensive cultivation of river eel
• Growing eels in swimming pools
• Growing glassy eel
• Reproduction of eels in artificial conditions
• Eel larvae
• Adaptation of eel larvae

Description of the European river eel

What kind of fish is the European eel?

The European eel is so different from ordinary fish that the question arises: is an eel a fish or not? The answer is simple: the European eel is a fish. The river eel family Anguillidae includes one genus Anguilla, which contains 15 species of eels. These are, as a rule, catadromous fish that inhabit the seas of the tropical and temperate zones, except the East and South Atlantic. The most famous species of eels that are grown in aquaculture are

• European eel - Anguilla anguilla (L.),
• American eel - A.rostrata (Le Sueur),
• Japanese eel - A.japonica Temminck et Schlegel.

In this article we will look at the European river eel.

Where does the European eel live?

Where is the eel fish found?

 

Where is the eel fish found? The European eel is a very flexible species, so it can live in both fresh and salt waters.
The European eel is found in Europe and North Africa, the Middle East. The European eel has spread very widely: the eel can be found from the North Cape to the Northern Tropic, from the White to the Black Sea; eel lives in large numbers on the Mediterranean coast, especially in Italy and the Balkans, Egypt and Syria, the North and Baltic seas; The eel lives in the rivers of the coast of Morocco, the Canary Islands, the Azores, Madeira, Great Britain, Ireland and Iceland.
The European eel lives in the Aegean Sea, Dardanelles, Marmara and Bosphorus, the eel lives in the Black Sea.
The European eel is found in the Baltic Sea, the Gulf of Finland and the Gulf of Bothnia.
Thanks to the wide habitat of the river eel, it received many names: in England the eel is called eel, in Germany, Holland, Denmark, Iceland, Norway - aal, in Spain, Italy - anguilla, in France - anguille, in Finland - ankerias, airokas, in Sweden - alen, al, in Croatia, Bosnia and Herzegovina, in Montenegro, Slovenia - jeryla, in Albania - balcha (balcha), in Bulgaria - zmiorka, in Poland - wegori, in Romania - anghila, tirag, in Slovakia and the Czech Republic - uhor, in Belarus, in Ukraine - vugor, in Latvia - suttis, in Lithuania - unguris, in Russia - eel, in Estonia - angerias.
Part of the European eel population in Belarus lives in lakes, penetrating through the Baltic Sea and migrating to the basins of the Western Bug, Pripyat, the Dnieper-Bug system, through the Neman and other Baltic rivers.
Part of the European eel population in Ukraine lives in lakes and rivers, penetrating through the Mediterranean, Marmara and Black Seas into the Danube, Dniester, and Dnieper, and the other part of the eel inhabits the Shatsk Lakes in Volyn through the Baltic Sea.
There are huge opportunities for eel cultivation in the Polesie lakes, as well as in the lakes of Belarus and the Baltic countries (Estonia, Lithuania, Latvia.

Where are eels found in Russia?

Where are eels found in Russia? Previously, the European eel can be found quite widely.
Through the Mediterranean, Marmara and Black Seas, the eel penetrates the Don and Kuban; through the Baltic Sea and its bays, the eel enters all the rivers flowing into it. Through the Neva, the eel penetrates into Lakes Ladoga and Onega, the river. Volkhov, through Narva to Lake Peipus, and from there to Pskovskoye. Through canals, the eel enters the Volga system, right up to its mouth. Found in the Caspian Sea. Previously settled in the Ural River, in the Orenburg region. The eel is found on Murman, occasionally enters the White Sea, from where single specimens rise to the Northern Dvina - Vychegda - Sysola. As an exception, it comes across in the lower reaches of Pechora.
Thus, there are huge opportunities for eel cultivation in lakes throughout the European part of Russia, the Caucasus, and also in Kazakhstan.
Habitat of the European eel
The European eel is a very unpretentious fish that can adapt and, accordingly, live in different types of reservoirs.
eels live in rivers, eutrophic and mesotropic lakes fnykh and even in dystrophic ones. The eel can live not only in fresh water bodies, but also in salt water bodies. However, eel grows much better in mesotrophic and eutrophic lakes than in dystrophic lakes.
According to its lifestyle, the eel is a bottom-dwelling fish that is nocturnal. During the day, the eel burrows into the ground almost completely, leaving only its head on the surface; the eel can burrow into the ground to a depth of 80 cm, or even deeper. The habitats of the river eel change with age.
During the first period of life in fresh water, the European eel lives near the shore in silty places that are overgrown with aquatic vegetation, where the eel finds not only reliable shelter from predators, but also food. Juvenile eels burrow shallowly into the bottom soil, while older eels burrow deeper into the soil. With age, the eel moves away from the shore of the lake to a deeper place, with a muddy bottom; the eel’s habitat is often littered, which gives it additional shelter. Eels hunt mainly at night on the surface of the bottom and in the lower layers of water. Eels move throughout the body of water, near the shore, and actively move through aquatic vegetation (cattail, reeds, reeds). The eel does not like places with a hard rocky bottom and therefore it avoids such places, which should be taken into account by the fish farmer when raising eel in a pond. When in danger, the eel quickly buries itself in the ground or hides in a shelter.

 

 

How do eels reproduce in nature?

Where do eels spawn? European eels spawn in the Sargasso Sea.
To spawn, eels from fresh water bodies slide into the sea, as a rule, upon the onset of the third stage of sexual maturity (on a six-point scale). But not all eels of the same age migrate at the same time; the closer the eels are to the sea, the earlier they begin their spawning migration.
For example, among migrating eels from the lakes of Belarus, individuals weighing 2.5 kg are often found, and individual specimens reach more than 3 kg, while the weight of migrating eels from the lakes of the Baltic states averages 0.7 kg and very rarely exceeds 1.5 kg.
After the eel spawns, the larvae of the European eel migrate over a period of 1-2 years to a distance of about 7 thousand km to the shores of Western Europe.

The larval stage of the European eel lasts 1.5-3 years.
How eels reproduce under artificial conditions will be described below.

Advantages and disadvantages of European eel when growing
Growing eels has a number of advantages:

• Excellent eel meat (protein content - 11-17%, fat -28-32%), which is in demand and is not inferior in quality to sturgeon;
• As a rule, the price of eel meat allows you to make a profit, even with intensive eel farming;
• The eel is unpretentious to living conditions, the eel lives everywhere except in overseas water bodies;
• It is possible to grow eels in polyculture with any type of fish;
• Eel, as a biomelifier, eats up weedy fish - ruffe, perch, bleak and others;
• The eel can live for some time (3-5 days) without water in a moist place in the grass, among aquatic plants.

But there is also a negative feature of the eel for the fish farmer:

• The eel is capable of crawling out of a body of water and migrating to rivers and other bodies of water.

What does a European eel look like?

 

Characteristic external signs of the European eel. The body of the river eel is elongated, serpentine, more or less round in the front part, and laterally compressed from the anus to the tail. The mouth is terminal and large. There are no pelvic fins, but the dorsal, caudal and anal fins merge to form a ribbon-like border encircling most of the body.

What does eel eat?

What does the European eel eat? Usually, during the daytime, the eel stops feeding and buries itself in the mud, exposing only its head, but if food floats nearby, the eel rushes at it. The eel feeds intensively in the summer, from May to September; in the winter, the eel hibernates, burrowing into the bottom soil.
The food spectrum of the European eel is very diverse; the eel eats mollusks, insect larvae, crustaceans, fish and other aquatic organisms. Therefore, the eel is considered a euryphage.
In spring it is very voracious, the eel feeds on leeches, low-chaete worms, mollusks, stoneflies, mayfly larvae, dragonflies, chironomids, caddis flies, lower and higher crustaceans, fish (ruff, perch, spined loach, rudd, bleak, roach).
Vitreous eels, after being planted in ponds, are omnivorous for the first two years, but mainly the eel feeds on lower crustaceans and small larvae of various insects, and occasionally algae.
In the second year of life, individual eels begin to hunt for fish, after which they significantly outstrip their relatives in growth. But, as a rule, the eel feeds on fish in the third year of life in fresh water.
Subsequently, there are no major differences in the nutrition of eels of different ages.
Eels under 8 years old live in all zones of the lake and, being voracious, they eat all the food they encounter, while eels older than 8 years live in the deep zone of the reservoir, where the species composition of food is limited. Therefore, even during the season of intensive feeding, the eel can starve.
When growing eel in a pond or lake, it competes with bream, silver bream, ide, tench, perch, ruff, and roach. But competitive
tion is small, since the eel is omnivorous. In addition, the eel feeds by swarming in the mud, eating food that is inaccessible to other fish. At the same time, the eel eats its competitors - perch, ruffe and other small fish, freeing the reservoir from trash fish.
Cannibalism is possible in the eel, but its nature is unclear, since it does not always occur.

How fast does an eel grow?

In the lakes of Belarus, eels longer than 1 m and weighing 2-3 kg or more were often found.

 

Obtaining juvenile river eels

Due to severe anthropogenic pollution of coastal sea waters and a large number of hydraulic structures on rivers, the natural entry of eels into rivers has practically ceased. Therefore, the European eel is an invader in inland waters; its quantity is determined by the scale of stocking.
The material for stocking lakes is the glassy larvae of the European glassy eel, purchased in Western Europe, and the larvae of the American eel, imported from Cuba. The average weight of eel when exported varies. 1 kg contains from 2,300 - 3,000 pieces (France), to 3,000 - 4,000 pieces (England) and 6,000 - 7,000 pieces (Italy). Eel larvae are transported at a water temperature of 4-12°C in special frames placed in boxes. The colonization of water bodies by eel larvae occurs at a water temperature of 8-12°C.

Growing river eel to commercial fish

Stocking density of river eel

In Poland, the density of eel stocking in lakes is determined depending on the composition of the ichthyofauna: in whitefish 40-60, in bream - 170-260, in zander - 260-300, in line-pike - 40 pieces per hectare.

Commercial sizes of European eel

Commercial sizes of the European eel: in the Baltic states - 55, in Belarus - 60, in Ukraine - 50 cm. The eel reaches this size in the 7-8th year, more often - in the 9-10th year after landing in the lake. In the 5th year of life in fresh water, eels with a length of more than 60 cm and an average weight of 500-1000 g make up about 40% of the herd. It is necessary to catch this part of the population without waiting for the onset of the downstream stage.
They catch eels with nets, meshes, eel traps, nets with 10 hooks, and an electrofishing unit (ELU-3).
Fish productivity when growing eels in a pond
The fish productivity of eels in the lakes of Belarus reaches 0.03-1 kg/ha, in Estonia - about 1 kg/ha (industrial return - up to 15%), in Western Germany - 6-15 kg/ha. Eastern Germany - from 3.1 to 15-60 kg/ha. It is estimated that to obtain a fish productivity of 1 kg of eel from 1 hectare of a commercial-sized lake, it is necessary to introduce 5 fry or 10-15 glassy eels per hectare. In the lakes of Western Germany, having introduced yearlings at 65-70 pcs/ha, they caught 6.8 kg/ha, and with a stocking density of 195 pcs/ha - 16.9 kg/ha.

Intensive cultivation of river eel

Intensive cultivation of eels under controlled conditions is widely practiced: eels are grown in cages and pools supplied with water mainly through the discharge of thermal wastewater from energy facilities using granulated feed, other artificially prepared feed or feed mixtures.

Growing eels in swimming pools

In thermal pools, eel growth can be quite high: in 20 months. at a water temperature of 23°C and feeding with meat, the average weight of eels increased from 2 to 520 g. In Western Germany, commercial eels were successfully grown in trays in thermal waters. With a stocking density of vitreous eels of 60 thousand pieces/m3, the weight of fish in less than a year ranged from 30 to 160 g, and the yield of fish products was 150 kg/m3. The feed used was a mixture of 50% fish and 50% dry granulated feed. The daily ration at a temperature of about 16°C was 3-4% of the body weight of the fish with a feed consumption of 4-5 units. per unit weight gain.

Growing glassy eel

There are 2 methods of growing glassy eel:
1) intensive (when feeding in cages produces eels with an average weight of 500 g with a fish product yield of 30-50 kg/km3 and more in 20-24 months);
2) extensive (when larvae invade water bodies - ponds, lakes, reservoirs). With the second method, it is possible to catch only 20-40% of the planted amount of fish and obtain eel fish products of 5-10 kg/ha.

 

Reproduction of eels in artificial conditions

Thanks to the introduction into practice of injecting fish with gonadotropic hormones, it became possible to obtain mature reproductive products - first sperm, and a little later - caviar.
Male European eels do not reach puberty in freshwater conditions. Under natural conditions, only spermatogonia are found in males during the transition to the silver eel stage at the 4-5th year of life in fresh water, when they reach a length of 45-50 cm and an average weight of 125-200 g. They remain in this state until the onset of catadromy. migration.
Mature sperm can only be obtained under the influence of injections of gonadotropic drugs - choriogonin and the pituitary glands of carp; for example, males become fluid 48-53 days after 7-11 injections with a total dose of the drug from 17.5 to 27.5 IU/kg.
The duration of sperm movement at a temperature of 19-23°C in undiluted ejaculate in the light is 10-15 minutes, in the dark - up to 80 minutes, in a diluted artificial morsea water at the same temperature in the light - 15-22 minutes. Males stimulated by hormones remain fluid for up to 100-120 days. Sperm frozen in liquid nitrogen retains its quality. Mass migration of eels from water bodies of Ukraine, Belarus, the Baltic states and Russia occurs in spring (April-May) and autumn (August-September).
Like males, females do not reach puberty in the natural conditions of freshwater bodies. Migrating silver eels aged 5-15 years had oocytes with a diameter of 0.13-0.22 mm, their gonads were at stage II or at the beginning of stage III of maturity. In females over the age of 10 years, oocyte resorption is often observed in fresh waters.
For hormonal stimulation, it is preferable to use males four to five years old and females six to ten years old in fresh water, when degenerative changes in the gonads have not yet occurred. It occurs most effectively when fish are 70-80 cm long and weigh 500-800 g.
The process of maturation of females under artificial conditions lasts 150-220 days using 8-10 weekly injections of a suspension of acetonated pituitary gland of carp or carp at a dosage of 1-15 mg per fish, causing spontaneous release of eggs. The remaining caviar is strained off.
The fertility of eels is high. The absolute fertility of a female American eel with an average weight of 760 g is 2.5 million eggs per 1 kg of body weight. The European eel weighing 0.5-1.2 kg has an absolute fecundity of 0.67-2.63 million eggs, a relative fecundity of 1.3-1.6 million eggs per 1 kg of body weight.
Since there is no external sexual dimorphism, breeders are selected by sex based on their length. All fish longer than 51 cm are classified as females. In addition, in migratory males the relative diameter of the eye is somewhat larger. Among males, individuals weighing more than 200 g were rarely found. Eels intended for artificial breeding are transported by road or air in rigid containers aerated with oxygen (one fish weighing 500-800 g per 10 liters of water) or in plastic bags filled with 1.5- 2.0 liters of water and oxygen. After landing the fish, the water is changed to remove mucus 3-4 times. The water temperature should not exceed 12-14°C, and the transportation time should not exceed 6-8 hours.
After overexposure and acclimatization, the fish are placed in pools with artificial sea water, where shelters for eels are constructed in the form of asbestos-cement pipes. At this time the eel is not fed. The optimal water temperature is 20-22°C.
To catch and fix eels, large mesh bags with a diameter of 10-20 and a length of 60-90 cm are used.
European eel eggs contain a drop of fat. The fertilized egg of the European eel has a small perivitelline space. Within 22 hours after fertilization, cleavage, blastula formation, and gastrulation are completed. Hatching of larvae under experimental conditions begins after 46-48 hours, mass hatching - after 50-60 hours. The head is separate, the eyes are not pigmented, the mouth and anus are closed. The larvae live in artificial sea water for 3.5 days, during which time the yolk sac is almost completely absorbed. In the Japanese eel, hatching occurs after 38-45 hours. The eels live for 5-14 days. On the 4-5th day, the mouth and anus open. On the 14th day, the length of the larvae reaches 7 mm.

Eel larvae

Eel larvae - leptocephali - migrate to the shores of the mainland, turning into glassy eels, and enter fresh waters. During the feeding process, they go through the stages of pigmented, yellow (or green) and silver eels. The acquisition of a silver color indicates readiness for spawning migration.
The larval form of the eel retains its glassiness up to a size of 75 mm, the American one - 65 mm. When transformed into a juvenile form, its length is reduced by 10 mm.
Eel larvae in the glassy stage are purchased from France from January to March, when they appear off the coast of Western Europe. During this period, the ponds of central Russia are still under ice, which raises the problem of raising larvae in industrial installations.

 

Adaptation of eel larvae

Adaptation of eel larvae. Larvae with an average weight of 0.33 g, delivered from France, are kept without feeding for 10 days in running water at a temperature of 6-8°C.
The eels are pre-adapted to the pool water temperature for 24 hours. The temperature is increased or decreased at a rate of 0.2-0.3 degrees/hour. The density of eel planting is from 10 to 200 pcs/l of water, or in a weight ratio from 1:300 to 1:15, respectively.
When the larvae are kept in a pool, they are located in groups, often in shaded areas, actively reacting to light and noise. For glassy eels, the threshold carbon dioxide content depends on water temperature and ranges from 22-300 mg/l. Optimal holding conditions: temperature - no higher than 5-8°C, planting density - from 50 to 100 pcs/l.
It is practiced to grow glassy eel in various containers, where vegetable crops (tomatoes and watercress) are cultivated using a hydroponic method with a closed water exchange cycle. The operating principle of the installation is based on the circulation of water in containers during the process of irrigating vegetable crops, after which the water enters the biofilters with expanded clay that absorb nitrates. The water filtered by the plant rhizomes then enters an activated carbon filter. A turnover of 600 liters of water lasts 1 hour.
A solar collector is used to heat water. The eel is fed daily for the first two weeks, once at midnight. The meat of crustaceans, as well as marine or freshwater fish, crushed to a pulpy state, is placed on special floating tables made of mesh. The temperature in mid-May is up to 25°C, pH - 7, nitrites - up to 50 mg/l, hardness 2-10°, oxygen content - more than 6.5 mg/l.
A 500-liter system contains 5.7 kg of glassy eel, and a 65-liter system contains 0.2 kg. The initial weight in March is 0.4 g, the final weight is after 4 months. - 0.8 g. Waste - 20-30%, feed ratio - no more than 7-13. The planting density in a 500-liter container is 11.8 thousand, in a 65-liter container - 10 pcs/l.

Earthworms grown on waste from livestock farms serve as excellent food for eels.