Sources : Eel

Aristotle [ca. 350 BCE] (De animalibus, Book 4, 11.2; 6, 13.7; 6, 15.1-2): [Book 4, 11.2] the eel is neither male nor female, nor is anything produced from them. [Book 6, 13.7] All the male fish have semen, except the eel, and this one has neither semen nor ova. [Book 6, 15.1-2] Eels are not produced from sexual intercourse, nor are they oviparous, nor have they ever been detected with semen or ova, nor when dissected do they appear to possess either seminal or uterine viscera ; and this is the only kind of sanguineous animal which does not originate either in sexual intercourse or in ova. It is, however, manifest that this is the case, for, after rain, they have been reproduced in some marshy ponds, from which all the water was drawn and the mud cleaned out; but they are never produced in dry places nor in ponds that are always full, for they live upon and are nourished by rain water. It is plain, therefore, that they are not produced either from sexual intercourse or from ova. Some persons have thought that they were productive, because some eels have parasitical worms, and they thought that these became eels. This, however, is not the case, but they originate in what are called the entrails of the earth, which are found spontaneously in mud and moist earth. They have been observed making their escape from them, and others have been found in them when cut up and dissected. These originate both in the sea and in rivers wherein putrid matter is abundant; in those places in the sea which are full of fuci, and near the banks of rivers and ponds, for in these places the heat causes much putridity. This is the mode of generation in eels. - [Cresswell translation, 1887]

Pliny the Elder [1st century CE] (Natural History, Book 9, 2; 9, 26-27; 9, 38-39; 9, 46; 9, 74; 9, 88; 10, 77)): [Book 9, 2] But the largest number of animals and those of the largest size are in the Indian sea, among them ... eels in the river Ganges [grow] to 300 feet. [Book 9, 26-27] ...other sea-fish are long, as the lamprey and the conger. ... Long slippery fish like eels and congers generally have two fins...[Book 9, 38] Eels live eight years. They can even last five or six days at a time out of water if a north wind is blowing, but not so long with a south wind. But the same fish cannot endure winter in shallow nor in rough water; consequently they are chiefly caught at the rising of the Pleiades, as the rivers are then specially rough. They feed at night. They are the only fish that do not float on the surface when dead. There is a lake called Garda in the territory of Verona through which flows the river Mincio, at the outflow of which on a yearly occasion, about the month of October, when the lake is made rough evidently by the autumn star, they are massed together by the waves and rolled in such a marvelous shoal that masses of fish, a thousand in each, are found in the receptacles constructed in the river for the purpose. [Book 9, 39] The lamprey [murena] spawns in any month, although all other fish have fixed breeding seasons. Its eggs grow very quickly. Lampreys are commonly believed to crawl out on to dry land and to be impregnated by copulating with snakes. Aristotle gives the name of zmyrus to the male fish which generates, and says that the difference is that the lamprey is spotted and feeble whereas the zmyrus is self-colored and hardy, and has teeth projecting outside the mouth. In Northern Gaul all lampreys have seven spots on the right jaw arranged like the constellation of the Great Bear, which are of a bright golden color as long as the fish are alive, and are extinguished when they are deprived of life. [Book 9, 46] The notion that [the octopus] gnaws its own arms is a mistake, for this is done to it by the congers... [Book 9, 74] Eels rub against rocks and the scrapings come to life; this is their only way of breeding. [Book 10, 77] these there is no male or female, as also there is no sex in eels and all the species that are neither viviparous nor oviparous... [Book 9, 88] Violent animosity between the mullet and the wolf-fish, and between the conger and the lamprey, which gnaw each other's tails. ... congers tear a polyp [octopus] to pieces. - [Rackham translation]

Saint Ambrose [4th century CE] (Hexameron, Book 5, 7): ...can this be more intolerable than the poison which is no obstacle to the sea-murena in dealing with her mate? When invited, she does not fail to respond and embraces the slimy serpent with great affection. ... When the viper, the deadliest kind of animal and the most cunning of the whole species of serpents, evinces a desire for copulation, he searches for a sea-murena already known to him or he seeks for a new mate. Proceeding toward the shore, he makes his presence known by a hissing sound, whereby he invites conjugal embrace. The sea-murena does not repulse the appeal and yields to the poisonous serpent the desired enjoyment of their conjugal bond. ... That is an adulterous offense against nature. It is a lesson which is taught us by the willing union of sea-murena and viper, a union not grounded on similarity of species, but on ardent desire. ... The murena, which is said to be somewhat harmful, is a choice table food. - [Savage translation, 1961]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6.41): The eel (anguilla) was given its name from its similarity to a serpent (anguis). Eels originate from mud; hence, when one is caught, it is so slippery that the tighter you hold it, the more quickly it slips away. They say that the river Ganges, in the East, produces eels thirty feet long. When eels are killed in wine, whoever drinks it then develops a distaste for wine. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.2; 7.22; 7.29; 7.40; 7.51): [Thomas describes the eel under the names anguilla, congris, gonger and murenis.] [Fish 7.2] An eel [anguilla] is a fish, as Jerome says, in appearance like a serpent, whence it received its name from the word angue (snake). The harder you squeeze it, the faster it slips away. It is difficult to skin. They say that it is born from the slime of other fish. Pliny says that there is no male or female sex in eels, for no eggs are found in them. Most often they rub themselves against the rocks; those rubbings come to life, and there is no other way of procreating them. If an eel is killed in wine, as Isidore says, those who drink it have an aversion to wine. They are moved by the sound of thunder. They enjoy clear river waters. They are predatory to some fishes of inferior power, but especially when they are found with eggs. Eels, as Aristotle and Pliny say, live for many years, but they last six days without water, and this when the wind is blowing from the North; but when the South wind blows, they live for fewer days without water. They cannot live in shallow water in winter, and they do not easily tolerate turbid waters. And for this reason, in the absence of the Pliades, because then the water is disturbed by the opposite winds, that is to say, they are mostly caught around the time of Vergiliarum. They feed at night. Eels are the only fish that do not float when they are dead, except when they are dissolved in the water when they putrefy. As the Experimentator says, the fat of the eel heals the ears. It is a hard to kill, and lives even when it is flayed. It must be cooked more, otherwise its flesh is harmful. It is more suitable to be roasted in the fire, because its bad quality evaporates. In the river Ganges there are eels thirty cubits long. [Fish 7.22] As Pliny says, the conger fishes (congris) of the sea are long in shape, like moray eels; yet they have a much larger body. Their meat is very sweet to eat. They are impregnated by a strong wind blowing. By these fishes are signified those who, having the long-suffering of hope, are also great in virtue. They become the delicious fish of Christ, doing the will of his Father. And therefore, with the blowing wind of the Holy Spirit, which rushed violently upon the apostles, they are imbued with the fear of God with the fruit of good works. [Fish 7.40] The gonger [conger] fish is indeed large and robust. This, as Pliny says, has enmity with the moray eel and other fish, so much so that they cut off each other's tails. But it is strong enough to tear the octopus with the strength of its teeth. [Fish 7.51] Morays [murenas] are of the female sex only and are conceived by a snake, and for that reason they go out into the dry land to copulate. Hence they are lured by the fishermen with the hissing of snakes. Ambrose says that when the snake comes to the moray to mate with it, it first vomits out all its poison. Here it is signified how much kindness ought to be shown by a man towards a woman, who certainly came together in this, that they might be two in one flesh. Moray are killed with clubs and hammers only with difficulty; they can hardly be killed by being struck on the head, but if struck on the tail they are immediately killed. The moray spawns every month, while other fish spawn at a fixed time. Its eggs grow very quickly. Aristotle calls the mirna [moray] the male that begets, and does not say that they are conceived by a serpent; he also says that there is a difference in these, which are various and shapeless; the mirnus is single-colored and robust; it has teeth outside its mouth. Pliny: In northern Gaul, all the moray have seven spots on their right cheek, which, in the shape of the Dipper [constellation], shine with a certain vigor, but are extinguished at the same time the soul dies. They are driven into a frenzy by the taste of vinegar. Aristotle: It is dangerous to take moray eels as food, unless they are first boiled in wine very well and for a long time, and carefully seasoned with aromatic species, and especially with pepper: for they show that they abound in poisonous humors, and therefore do not yield to easy cooking. As Pliny says, the murres like to keep themselves between the rushes and the trees, so that if they happen to be captured, they can escape from the net by twisting it multiple times. Moray have a poisonous bite, but the bite is cured by the ashes of their heads. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.26): And yet he sayth, that the Cunger hath manye wiles, and is wittye and wylye of getting of meate: for when hee seeth meate on a hooke, hee dreadeth the hooke, and biteth not the baite, but holdeth the hooke with his finnes, and letteth it not passe till hée have gnawen the meate. - [Batman]