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EEL

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Originally appearing in Volume V09, Page 9 of the 1911 Encyclopedia Britannica.
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EEL . The See also:

common See also:freshwater eel (See also:Lat. See also:anguilla; O. Eng. cel) belongs to a See also:group of soft-rayed fishes distinguished by the presence of an opening to the See also:air-See also:bladder and the See also:absence of the pelvic fins. With its nearest relatives it forms the See also:family Muraenidae, all of which are of elongated cylindrical See also:form. The peculiarities of the eel are the rudimentary scales buried in the skin, the well-See also:developed See also:pectoral fins, the rounded tail fin continuous with the dorsal and ventral fins. Only one other See also:species of the family occurs in See also:British See also:waters, namely, the conger, which is usually much larger and lives in the See also:sea. In the conger the eyes are larger than in the eel, and the upper See also:jaw overlaps the See also:lower, whereas in the eel the lower jaw projects beyond the upper. Both species are voracious and predatory, and feed on almost any See also:animal See also:food they can obtain, living or dead. The conger is especially fond of squid or other Cephalopods, while the eel greedily devours carrion. The common eel occurs in all the See also:rivers and fresh waters of See also:Europe, except those draining towards the See also:Arctic Ocean, the See also:Black Sea and the See also:Caspian Sea. It also occurs on the See also:Atlantic See also:side of See also:North See also:America. The conger has a wider range, extending from the western and See also:southern shores of See also:Britain and See also:Ireland to the See also:East See also:Indian See also:Archipelago and See also:Japan.

It is common in the Mediterranean. The ovaries of the eel resemble somewhat those of the See also:

salmon in structure, not forming closed sacs, as in the See also:majority of Teleostei, but consisting of laminae exposed to the See also:body cavity. The laminae in which the eggs are produced are very numerous, and are attached transversely by their inner edges to a membranous See also:band See also:running nearly the whole length of the body-cavity. The majority of the eels captured for See also:market are See also:females with the ovaries in an immature See also:condition. The male eel was first discovered in 1873 by Syrski at See also:Trieste, the testis being described by him as a lobed elongated See also:organ, in the same relative position as the ovary in the See also:female, surrounded by a smooth See also:surface without laminae. He did not find ripe spermatozoa. He discovered the male by examining small specimens, all the larger being female. L. Jacoby, a later observer, found no See also:males exceeding 19 in. in length, while the female may reach a length of 39 in. or more. Dr C. G. J.

Petersen, in a See also:

paper published in 1896, states that in See also:Denmark two kinds of eels are distinguished by the fishermen, namely, yellow eels and See also:silver eels. The silver eels are further distinguished by the shape of the snout and the See also:size of the eyes. The snout in front of the eyes is not See also:flat, as in the yellow eels, but high and compressed, and therefore appears more pointed, while the eyes are much larger and directed outwards. In both kinds there are males and females, but Petersen shows that the yellow eels See also:change into silver eels when they migrate to the sea. The sexual See also:organs in the silver eels are more developed than in the yellow eels, and the former have almost or entirely ceased to take food. The male silver eels are from 111 to 19 in. in length, the females from 161 to about 39 in. It is evident, therefore, that if eels only spawn once, they do not all reach the same size when they become sexually mature. The male conger was first described in 1879 by See also:Hermes, who obtained a ripe specimen in the See also:Berlin See also:Aquarium. This specimen was not quite 21 ft. in length, and of the numerous males which have been identified at the See also:Plymouth Laboratory, none exceeded this length. The large See also:numbers of conger above this size caught for the market are all immature females. Female conger of 5 or 6 ft. in length and weighing from 30 to 50 lb are common enough, and occasion-ally they exceed these limits. The largest recorded was 8 ft.

3 in. See also:

long, and weighed 128 lb. There is every See also:reason to believe that eels and conger spawn but once in their lives, and See also:die soon after they have discharged their generative products. When kept in aquaria, both male and female conger are vigorous and voracious. The males sooner or later cease to feed, and attain to the sexually mature condition, emitting ripe milt when handled and gently squeezed. They live in this condition five or six months, taking no food and showing See also:gradual wasting and disease of the bodily organs. The eyes and skin become ulcerated, the sight is entirely lost, and the bones become soft through loss of See also:lime. The females also after a See also:time cease to feed, and live in a See also:fasting condition for five or six months, during which time the ovaries develop and reach See also:great size and See also:weight, while the bones become soft and the See also:teeth disappear. The female, however, always See also:dies in confinement before the ova are perfectly ripe and before they are liberated from the ovarian See also:tissue. The absence of some necessary condition, perhaps merely of the pressure which exists at the bottom of the sea, evidently prevents the See also:complete development of the ovary. The invariable See also:death of the See also:fish in the same almost ripe condition leads to the conclusion that under normal conditions the fish dies after the mature ova have been discharged. G. B.

Grassi states that he obtained ripe male eels, and ripe specimens of See also:

Muraena, another genus of the family, hi the whirlpools of the Strait of See also:Messina. A ripe female Muraena has also been described at See also:Zanzibar. Gravid female eels, i.e. specimens with ovaries greatly enlarged, have been occasionally obtained in fresh See also:water, but there is no doubt that, normally, sexual maturity is attained only in the sea. Until See also:recent years nothing was known from See also:direct observation concerning the See also:reproduction of the common eel or any species of the family. It was a well-known fact that large eels migrated towards the sea in autumn, and that in the See also:spring small trans-See also:parent eels of 2 in. in length and upwards were common on the See also:shore under stones, and ascended rivers and streams in vast swarms. It was reasonable, therefore, to infer that the mature eels spawned in the sea, and that there the See also:young were developed. A group of See also:peculiar small fishes were, however, known which were called Leptocephali, from the small proportional size of the See also:head. The first of these described was captured in 17b3 near See also:Holyhead, and became the type of L. Morrisii, other specimens of which have been taken either near the shore or at the surface of the sea. Other forms placed in the same genus had been taken by surface fishing in the Mediterranean and in tropical ocean currents. The See also:chief peculiarities of Leptocephali, in addition to the smallness of the head, are their ribbon-like shape and their glassy transparency during See also:life. The body is flattened from side to side, and broad from the dorsal to the ventral edge.

Like the eels, they are destitute of pelvic fins. and no generative organs have been observed in them (see fig.). In 1864 the See also:

American naturalist, T. N. Gill, published the conclusion that L. Morrisii was the young or larva of the conger, and Leptocephali generally the young stages of species of Muraenidae. In 1886 this conclusion was confirmed from direct observation by Yves Delage, who kept alive in a tank at See also:Roscoff a specimen of L. Morrisii, and saw it gradually transformed into a young conger. From 1887 to 1892 See also:Professor Grassi and Dr Calandruccio carried on careful and successful researches into the development of the Leptocephali at See also:Catania, in See also:Sicily. The specimens were captured in considerable numbers in the See also:harbour, and the transformation of L. Morrisii into young conger, and of various other forms of Leptocephalus into other genera of Muraenidae, such as Muraena, Congromuraena and Ophichthys, was observed. In 1894 the same authors published the announcement that another species of Leptocephalus, namely, L. brevirostris, was the larva of the common eel. This larval form was captured in numbers with other Leptocephali in the strong currents of the Strait of Messina.

In the See also:

metamorphosis of all Leptocephali a great reduction in size occurs. The L. brevirostris reaches a length of 8 cm., or a little more than 22 in., while the perfectly-formed young eel is 2 in. long or a little more. The See also:Italian naturalists have also satisfied themselves that certain pelagic fish eggs originally described by Raffaele at See also:Naples are the eggs of Muraenidae, and that among them are the eggs of Conger and Anguilla. They believe that these eggs, although See also:free in the water, remain usually near the bottom at great depths, and that fertilization takes See also:place under similar conditions. No fish eggs of the See also:kind to which reference is here made have yet been obtained on the British coasts, although conger and eels are so abundant there. Raffaele described and figured the larva newly hatched from one of the eggs under See also:consideration, and it is evident that this larva is the earliest See also:stage of a Leptocephalus. Although young eels, some of them more or less flat and transparent, are common enough on the coasts of Great Britain and north-western Europe in spring, neither eggs nor specimens of Leptocephalus brevirostris have yet been taken in the North Sea, See also:English Channel or other shallow waters in the See also:neighbour-See also:hood of the British Islands, or in the Baltic. Marked eels have been proved to migrate from the inmost See also:part of the Baltic to the Kattegat. Recently, however, See also:search has been made for the larvae in the more distant and deeper portions of the Atlantic Ocean. In May 1904 a true larval specimen was taken at the surface See also:south-See also:west of the See also:Faeroe Islands, arid another was taken 40 M. north by west of See also:Achill Head, Ireland. In 1905 numbers were taken in deep water in the Atlantic. The See also:evidence at See also:present available indicates that the spawning of mature eels takes place beyond the 10o See also:fathom See also:line, and that the young eels which reach the See also:coast are already a See also:year old.

As eels, both young and old, are able to live for a long time out of water and have the See also:

habit of travelling at See also:night over See also:land in wet grass and in See also:damp See also:weather, there is no difficulty in explaining their presence in See also:wells, ponds or other isolated bodies of fresh water at any distance from the sea. See " The Eel Question," See also:Report U.S. See also:Commissioner of See also:Fisheries for 2879 (See also:Washington, 1882); J. T. See also:Cunningham, " Reproduction and Development of the Conger," Journ. See also:Mar. Biol. Assn. vol. ii.; C. G. J. Petersen, Report See also:Dan. Biol.

Station, v. (1894) ; G. B. Grassi, Quart. Journ. Mic. Sci. vol. xxxix. (1897). (J. T.

End of Article: EEL

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