Fig. 3.—Blind salamander from an artesian well at San Marcos, Texas (Typhlomolge).
Chologaster papilliferus detects its food entirely by the sense of touch. Two which were kept in an aquarium for over a year were starved for a few days. They became very nervous, continually swimming along the sides of the aquarium. Asellus was introduced. These, even if quite near, produced no effect if moving in front of the Chologaster. The moment one came in close proximity to the fish from any direction, by a flashlike motion it was seized. None of them were swallowed. The fish became very alert after the introduction of the sowbugs, and when swimming forward would strike at a part of a leaf if it came in contact with the head of the fish. It seemed evident that the eye gave no information of the character of the object. As Asellus was not altogether to their taste, Gammarus was introduced. One of these swimming rapidly toward the chin of the Chologaster from behind and below was instantly seized when it came in contact with the fish. The eye could not have located the Gammarus at all. The action is in very strong contrast to the action of a sunfish, which detects its food by the sight. It is undoubtedly this peculiar method of locating and securing food which has enabled the Amblyopsidæ to establish themselves in caves.
The Chologaster in general make-up is like Amblyopsis, but is somewhat longer-jointed. It sits with its pectorals extended. When it moves horizontally for some distance the pectorals are usually pressed to the sides, the propelling being done largely by the tail very much after the manner of a salamander, which it resembles. In swimming toward the surface it uses its pectoral fins chiefly, and the fish usually sinks to the bottom as soon as its efforts to raise itself are stopped.
Individuals kept in aquaria with one end darkened either collected in the darkened area floating about, or under leaves or sticks in any part of the aquarium. They are frequently found under a floating board, where they float with the tops of their heads in contact with the board, their bodies slanting downward. They seek the dark, regardless of the direction of the rays of light. These characteristics they have, in great part, in common with the blind members of the family. The adult Amblyopsis frequently floats with its head to the top of the water, the tail sloping downward, and in swimming along ledges of rock the top of the head is applied to the ledge. I have captured many specimens simply by scraping my net along the surface of a ledge.
Typhlichthys, living in total darkness, has retained the habit of staying under floating boards, sticks, and stones. Miss Hoppin noticed that Troglichthys swims with its back to the sides of the aquarium, and I have repeatedly noted the same in the young of Amblyopsis up to fifty millimetres, and the still younger Amblyopsis frequently hides under rocks.
Amblyopsis.—The general impression given by Amblyopsis is that of a skinned catfish swimming on its back. The expressions, “They are catfish”; “They look as though they were skinned”; “They are swimming on their backs,” are heard from those who see these fishes for the first time.
The largest individual secured by me measured 135 millimetres in total length. Individuals as large as this are rare. The usual length of an adult is about 90 millimetres. One individual was mentioned to me at Mammoth Cave having a length of 200 millimetres!
Amblyopsis is found in pools in the cave streams it inhabits. I have secured as many as twelve from a pool perhaps ten by fifty feet in size. Very rarely they are to be found in the riffles connecting the pools. I have seen them lying at the bottom, or swimming, or rather gliding, through the water like “white aquatic ghosts.” In the aquarium they lie at the bottom or at various depths in the water, their axes making various angles with the horizontal, their pectorals folded to their sides. When swimming slowly it is chiefly by the use of the pectorals. The strokes of the pectoral are lazily given, and the fish glides on after a stroke till its impetus is exhausted, when another stroke is delivered. The fishes frequently roll slightly from side to side at the exhaustion of the result of a stroke. When swimming rapidly the pectorals are folded to the sides, and their locomotion is then similar to that of a salamander—by the motion of the tail. They readily adjust themselves to different depths, and are usually perfect philosophers, quiet, dignified, unconcerned, and imperturbed, entirely different from such eyed species as minnows and sunfishes which are sometimes found in caves and which are much more readily disturbed by any motion in the water, making it almost impossible to capture them when found in the caves. The pectorals are also almost exclusively used when quietly rising in the water. At such times the pectorals are extended laterally and then pressed to the sides, beginning with the upper rays. A downward stroke is delivered in this way not quickly, but with apparent lazy deliberation. In swimming the pectorals are brought forward upper edge foremost. The center of gravity seems to be so placed in regard to their various axes that the fish does not lose its balance whatever its position. They float horizontally in the water without any apparent effort to maintain their position, or with the main axis inclined upward, with the snout sometimes touching the surface of the water, apparently lifeless. Once one was seen resting on its tail in a nearly vertical position, and one while quietly swimming was once seen to leisurely turn a somersault and swim on undisturbed. At another time the same individual rolled completely over. When one of them is kept out of the water for a short time it frequently goes in a corkscrew-shaped path through the water, continually spinning around its long axis. In their quiet, floating position it is difficult to determine whether they are alive or not.
