Plate 19.
P. H. GOSSE, del. LEIGHTON, BROS.
TWO-SPOTTED SUCKER.
Their form is flattened; they have a broad shovel-shaped muzzle, prominent eyes, looking rather upwards, and the head much widened behind; the head, indeed, constitutes more than one-fourth of the entire length; and at its hinder part, or where the gills open, is far wider than any other part of the fish. They rarely exceed an inch and a half in length. The general hue above is pale red; but in some specimens they become a nearly uniform lake-purple, in others the hue is a clear orange; while yet in others it is almost white. A band of white, bounded by darker lines, almost invariably connects the two eyes. Frequently the hue of the body is varied by clouds and patches of dark reddish brown, which patches have a tendency to assume a constant pattern, quite recognisable when you look at a good many specimens together. In the hinder half and on the sides the ground colour is apt to be minutely divided or mottled, the interspaces being of a delicate azure or lilac; and when examined with a lens, the whole surface seems sown with gold dust. The dorsal fin is set very far back, and, as well as the caudal, is prettily pencilled with dark brown: the under parts are pearly white.
The eyes are exquisitely beautiful, and as they are prominent, very movable, and especially as they are moved quite independently of each other, they at once attract and fix the admiration of the beholder. The large pupil is of a deep lustrous green, the iris of the most brilliant orange gold, and the whole set as it were in the midst of a globe of the purest glass. On the whole I scarcely know of a more attractive little fish than this.
ITS HABITS.
This little Sucker is easily reconciled to captivity. I have in my aquariums some individuals which were captured nearly a year and a half ago; and they are still in the full enjoyment of health and activity. They are pleasing little things: they scuttle from spot to spot with a spasmodic sort of bustle, wagging their tails much from time to time, so that in movement as well as in form they remind one of tadpoles. They are generally seen, however, anchored to the sides of the vessel, or to the prominent knobs of the stones by their sucker, and here they remain for an indefinite time, sometimes for hours, at others only a few seconds, throwing their beautiful eyes about in insatiable curiosity, fanning the water with their transparent pectorals, or whisking the painted tail about. Now and then they make a sudden snap, doubtless at some passing animalcule, with an audible sound, and the emergence of a bubble of air from the top of the water, whence the muzzle is frequently projected. They have an awkward habit of throwing themselves out of a shallow vessel; and if you are not on your guard you may find your little pets dead and dry on the carpet. They are inquisitive little things; if a new stone or shell or tuft of serpulæ is put into their vessel they soon discover it, and may be seen exploring it in every part; and it is amusing, when you are examining them with a lens, to note how thoroughly mutual is the investigation; for you can see by the direction and motion of the eyes that the little fish is watching you as interestedly as you are observing him.
I do not think that the adhesion of the ventral sucker is effected exactly as has been supposed, by a vacuum produced in the area of the united ventral fins; but by the combined action of some minute fleshy sucking disks, which are arranged in two groups, in front of and behind the united fins. The conjoined fins do not appear to me to make a vacuum. The fish has a curious habit of coming to the surface of the water, and there floating perfectly still, back downward, the entire belly-surface dry. The ventral disk is then seen as a shallow cup, quite dry and shining. If touched, the little fish hurries along the surface, with some splashing, till it acquires impetus enough to go under at an oblique angle, when it presently turns over, and adheres to the bottom, or side of some stone. I have seen this practice frequently, but only, I think, at night.[87]
This principle of a vacuum produced by the retraction of the centre of a fleshy disk, while the margins remain in close contact with a solid body, is of extensive application in the lower forms of animal life, and especially in the class Echinodermata, comprising what are popularly known as Star-fishes, Sea-urchins, and Sea-cucumbers.