Surprising indeed is the variety of species of fishes contained in the Amazonian basin. Professor Agassiz, during his expedition, collected nearly two thousand, “for the most part,” as he observes—and which is still more surprising—“circumscribed within different limits, from Tabalinga to Para, where the waters differ neither in temperature, nor in the nature of their bed, nor in the vegetation along their borders. There are met with, from distance to distance, assemblages of fishes completely distinct from each other.”
Still more curious, perhaps, is the intensity with which life is manifested in these waters. All the rivers in Europe, from the Tagus to the Volga, do not nourish a hundred and fifty species of fresh-water fishes; and yet in a little lake near Manaos, called Lago Hyanuary, the surface of which hardly covers four or five hundred square yards, more than two hundred distinct species were discovered, the greater part of which have not been observed elsewhere.
Gymnotus, or Electric Eel.
In the forest pools, as well as in the marshy ponds and slow-flowing rivers of the Llanos, numbers of huge serpentlike heads may be seen bobbing above the surface; or a huge, thick-bodied, yellow, snake-like creature may be caught sight of gliding through the water. It is the gymnotus electricus, or electric eel,—one of the many curious inhabitants of this region,—from two to five, and even eight feet in length. Though really a fish, it resembles the eel, but is stouter in its proportions. It is nearly equal in thickness throughout. It has a rude, depressed, and obtuse head, and a compressed tail. So great is the electric power it possesses, that when in full vigour it is able to kill the largest animal, when it can unload its electric organs in a favourable direction. All other fish, knowing by instinct the deadly effects of its stroke, fly from the formidable gymnotus. When fish are struck, or any animals which enter the pools inhabited by gymnoti—to drink, or cool their bodies, heated by the burning sun of the Llanos—they become stupified, and thus easily fall a prey to the electrical tyrant.
The natives of Venezuela employ a cruel mode of catching the creatures, which, notwithstanding their nature, they use as food. Placing but little value on mules and horses, they collect a number of these animals, and, armed with harpoons and long slender rods, drive them with shouts towards a pool inhabited by gymnoti. The noise of the horses’ hoofs and the men’s shrieks make the fish issue from the mud, when the huge, hideous creatures swim on the surface of the water, and crowd under the bellies of the horses and mules. Some of the Indians climb the trees; others stand round the margin, urging forward the unfortunate animals, and preventing them from making their escape. The fish defend themselves by frequent discharges of their electric batteries. At first they seem likely to prove victorious. Some of the quadrupeds sink beneath the violence of the invisible strokes which they receive from all sides, and, stunned by the force and frequency of the shocks, disappear under water; others, with their manes erect and eye-balls wild with pain, strive to escape the electric storm which they have aroused, but are driven back by the shouts and long whips of the excited Indians. The livid, yellow eels, like great water-snakes, swim near the surface and pursue their enemy. After the conflict has lasted a quarter of an hour or so, the mules and horses appear less alarmed. They no longer erect their manes, and their eyes express less pain and terror. The eel-like creatures, instead of advancing as at first, swim to the shore, when the Indians attack them with their harpoons, and by means of a long cord attached to it, jerk the fish out of the water, without receiving any shock, as long as the cord remains dry.
Such is the description given by Humboldt, a witness of the extraordinary scene. The employment of their electric
powers is evidently spontaneous, and exhausts the nervous energy. Like voluntary muscular effort, it needs repose, and the creatures require an abundance of nourishment and rest before a fresh accumulation of electricity is produced.
In the dry season they form deep circular holes for themselves in the mud of water-courses, and marshes which remain filled with moisture, and they are thus able to support existence in their usual localities, while alligators and turtles have to retire to the larger pools or rivers. In the shallow ponds of the forest they are easily driven out with long poles.
Bates amused his native companions, who had thus caught some of the creatures, by showing them how the electric shock could pass from one person to another. They joined hands in a line, while he touched the biggest and freshest of the animals on the head with the point of his hunting-knife. He found, however, that the experiment did not succeed more than three times with the same eel when out of the water, for the fourth time the shock was scarcely perceptible.