Sources : Muraena

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:43): The Greeks call the murena muraena because it twists itself in circles. People say this fish only exists in the female sex and that it conceives by means of a snake; on this account it can be summoned and caught by fishermen making a hissing sound like a snake. It can be killed with difficulty by a cudgel blow, but immediately with a rod. It clearly has its vital principle in its tail, for when its head is beaten, it can scarcely be killed, but it dies immediately when the tail is struck. - [Barney, Lewis, et. al. translation]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.26; 18.1): [Book13.26] There is a Fish that is called Murena, a Lampray: that of his like conceiveth not, but of an Adder, which hée calleth to love with hissing, as Isidore saith lib. 12. cap. 6. The Greekes (he saith) call this fish yt is called Murena, Stairmam, for he holdeth himselfe in circles. They tell, that this fish is a Female, and conceiveth of the Serpent. And therefore Fishers call it with hissing and whisteling, and taketh her in that wise. Unneth she dyeth, though shée bee smit with a staffe: and if she be smit with a rod, she dieth anone. It is certaine that the soule of this fish is in ye taile, for they say unneth she is slain, though she be smit on the head. And if she be smit on the taile, or if the taile bée smitte of, she dyeth anone, as it is sayde. ... Also Jorath sayth, that the Serpent doth awaye his venim ere he gender with the Lampray: But when the deed of generation is done, he taketh his venim againe: and therfore in conceiving, the Lampraye taketh no venim of the Serpent, nor gendereth not of serpent kinde, but onely of his owne kinde, as he saith. - [Batman]