Eels are pre-eminently nocturnal animals. They always congregate at the darkest parts of the stews in which they are kept, and invariably select the darkest nights for their autumnal migration to the sea. Owing to the smallness of their gill aperture, the membranous folds of which, by closing the orifice when the eel is out of the water, prevents the desiccation of the branchiæ, they have the power of living a long time out of the water when the air is humid, and not unfrequently travel during the night over the moist surface of meadows or gardens in quest of frogs or other suitable food.
That eels are not devoid of sagacity is proved by many well authenticated anecdotes. "In Otaheite," says Ellis in his "Polynesian Researches," "they are fed till they attain an enormous size. These pets are kept in large holes two or three feet deep, partially filled with water. On the sides of these pits they generally remain, excepting when called by the person who feeds them. I have been several times with the young chief when he has sat down by the side of the hole, and by giving a shrill sort of whistle has brought out an enormous eel, which has moved about the surface of the water and eaten with confidence out of his master's hand."
The eel has many enemies, among others the common heron, who, in spite of the slippery skin of his victim, knows how to drive his denticulated middle claw into his body, or to strike him with his pointed bill. Yarrell relates that a heron had once struck his sharp beak through the head of an eel, piercing both eyes, and that the eel--no doubt remembering that one good turn deserves another--had coiled itself so tightly round the neck of the heron as to stop the bird's respiration: both were dead.
The London market is principally supplied with eels from Holland, a country where they abound. According to Mr. Mayhew, about ten millions of eels, amounting to a weight of 1,500,000 lbs., are annually sold in Billingsgate market. These figures show us at once that the multiplication of eels in our sluggish rivers, which only contain such fish as are comparatively speaking worthless, is a matter worth consideration, and powerfully pleads for the protection and transplantation of the elvers wherever they are likely to prosper.