Another fish (the anojas), common in the Amazon, takes shelter—for it cannot be said to build a nest—in a hollow log. It belongs to the genus Auchenipterus. Numbers of this fish are found crowded in dead logs at the bottom of the river. One examined by the Professor, was filled with fish of all sizes, from those several inches long to the tiniest young. The fish were so dexterously packed into the log from one end to the other, that it was impossible to get them out without splitting it open, when they were all found alive and in a perfectly good condition. They could not have been jammed artificially into the hollow wood in that way without injuring them.
Anableps.
We have heard of blind fish, but here is one—called by the Indians tralhote, and known to naturalists as the Anableps tetraophthalmus, signifying “four-eyed”—possessing four eyes. A membraneous fold, enclosing the bulb of the eye, stretches across the pupil, dividing the visual apparatus into the upper and lower half; a curious formation, suited to the peculiar habits of the anableps. These fishes gather in shoals on the surface of the water, their heads resting partly above and partly below the surface, and they move by a leaping motion somewhat like that of frogs on land. Thus, half in and half out of the water, they require eyes adapted for seeing in both elements, and the arrangement described just meets this want.
The Parrot-Fish.
The birds of the air have, in this region, their representatives in the water. Among them is the curious and handsome pirarara, or parrot-fish. It is a heavy, broad-headed creature, with a bony shield over the whole head. Its general colour is jet-black, its bright yellow sides deepening into orange here and there. The yellow fat of this fish has a curious property. The Indians assert that when parrots are fed upon it they become tinged with yellow, and they often use it to render their papagaios more variegated.
The Gymnotus.
On the Amazonian waters is found the carapus, called by the Brazilians sarapo, belonging to the genus Gymnotus; though far smaller than the electric gymnotus. They are very numerous, and the most lively of the whole group. Their motions are winding and rapid, like those of the eel; but yet different, inasmuch as they do not glide quickly forward, but turn frequent somersaults, and constantly change their direction.
Localisation of Fish.
The researches of Professor Agassiz prove that the localisation of species of fish in these waters is peculiarly distinct and permanent, their migrations being very limited—consisting chiefly in removing from shallow to deeper waters, and from these to shallow again, at those seasons when the range of the shore in the same water-basin is affected by the rise and fall of the river. Thus, the fishes found at the bottom of a lake covering, perhaps, a square mile in extent when the waters are lowest, will appear near the shores of the same lake when, at the season of high-water, it extends over a much wider area. In the same way, fishes which gather near the mouth of a rivulet at the time of low-water, will be found as high as its origin at the period of high-water; and those which inhabit the larger igarapes on the sides of the Amazon, when they are swollen by the rise of the river, may be found in the Amazon itself when the stream is low. There is not a single fish known to ascend from the sea to the higher courses of the Amazon at certain seasons, and to return regularly to the ocean.
The striking limitation of species within different areas does not, however, exclude the presence of certain kinds of fish simultaneously throughout the whole Amazonian basin. The piraracu, for instance, is found everywhere from Peru to Para; and so are a few other species more or less extensively distributed over what may be considered distinct ichthyological fauna. But these wide-spread species are not migratory. They have normally and permanently a wide range—just as some terrestrial animals have an almost cosmopolitan character—while others are circumscribed within comparatively narrow limits.