Popular Science Monthly/Volume 63/May 1903/Obituary Notice of a Lung-Fish




THERE died recently in the aquarium room of the department of zoology of Columbia University, a specimen of the African lungfish, Protopterus annectans. Here it had lived for nearly five years, thriving at the cost of generations of living earthworms and increasing in size nearly three-fold. From the fact that this interesting fish is relatively rare in aquaria, the present specimen is possibly deserving of a formal memorial notice.

It arrived at Columbia University in July, 1898, in a sun-baked clod of earth, in which under native conditions the fish lies dormant during the summer drought. In this state it had been living for several months, and during the interval it had been breathing air, thanks to its lung, in a very unfish-like way. Its earlier history may be written

Fig. 1. Fig. 2.

Clod of Earth containing Cocoon of Lung-fish. Fig. 1 shows entrance burrow, Fig. 2 remains of cocoon after escape of fish.

with tolerable accuracy. Its early life was spent in some African stream in the region of the Congo, where it had lived successfully hunting and unsuccessfully hunted, until the approach of the dry season. Then as the stream dried up, it had taken to the last pool, and when this in turn had dried, the fish, like its neighboring friends and relatives, had burrowed deep into the thickening mud, rolled itself up into a ball, secreted a mass of mucus about its coiled body, and made ready for a summer 'sleep.' One of its first precautions was to keep its nose uppermost and to see that its 'breath' found a passageway out of its slimy capsule into the open burrow: in this way, then, it could breathe throughout the summer, while awaiting dormantly the return of rains, and the melting of its 'cocoon.' In this stage in its history it came to be dug up, and, together with other cocoons and their surrounding clods of earth, was crated and shipped to Europe. I am told that the shippers take pains to surround the crate with iron gauze to preserve the fish from the attacks of rats on shipboard, and that the clods of earth are disposed in such a way that the sides containing the breathing apertures face outward so that the imprisoned fish run the least possible danger of becoming stifled.

The present shipment came into the hands of Professor H. O. Forbes, Director of the Public Museums of Liverpool, and through his kindness the present specimen was donated to Columbia. A photograph, Fig. 1, shows the cocoon just as it came to the present writer. The tubular burrow through which the fish worked its way into the mud is seen conspicuously, and one may note that it was somewhat crooked, in spite of the fact that part of its margin has been broken away in the present specimen. Its usual length appears to depend upon the character of the bottom; from two to five inches are the measurements stated. At the end of the burrow lies the cocoon, a roundish mass, brown in color, paper-like in texture, but greatly roughened on its outer surface by attachment to rootlets and foreign matter. Its inner surface, as one would expect from the mucous nature of the shell, is found to be smooth and delicate. Where the cocoon meets the outer burrow its shell is somewhat flattened, and here, near the side, it is perforated by a delicate straw-like tube, formed of dry mucus, which passes downward into the mouth of the fish, and through this the fish respires during the dry season. It has, indeed, been shown by Professor W. N. Parker that this tube passes within the mouth of the fish and conducts the air to the entrance of the fish's lung.

In liberating the fish from the cocoon, the usual procedure is to allow the mass to remain in warmish water until the earth softens and melts, but in the present case a shorter, but somewhat more perilous, course was adopted. One side of the block was cautiously sliced away until the side of the papery cocoon became visible: then the earthy margins of the opening were carefully removed, so that the process of liberating the fish could be observed. The entire mass was next placed in an aquarium in water slightly warmed. In a few moments slight movements of the fish could be seen through the papery shell; and upon lifting out the earthen block and touching the cocoon, a distinct croaking sound was heard several times. Replaced in water, the capsule soon softened and ruptured like wet paper, and for a moment a glimpse was had of the fish tightly rolled up, with its tail folded over the head and only a single thread-like limb protruded. This, however, was but for a moment, for with an energetic squirm the animal liberated itself and sank to the bottom of the aquarium. For a moment it lay motionless, then swam briskly around the aquarium, coming to the surface several times and gulping air. At this time it showed the crimson flush of blood in the tail region where, according to Wiedersheim, the skin aids the lung as a respiratory organ. The fish, as one might indeed have inferred from the size of the burrow in the clod of earth, proved to be small, measuring a little over five inches in length. It was, however, larger than one would have estimated from the diameter of the tubular opening and from the actual size of the cocoon, the latter measuring about two inches in length and one inch in thickness. In Fig. 2 is shown the remains of the cocoon after the escape of the fish, the upper portion of the papery case alone being preserved.

From the small size of the fish this was possibly its first season of æstivation. How long it had been out of the water was not known, but

Fig. 3. Lung-fish, Protopterus. Resting position in aquarium.

certainly this was a matter of several months. I have, indeed, learned from Dr. Forbes that a fish will sometimes survive a period of eight months out of water.

Shortly after its release from the cocoon the writer's colleague, Dr. Edward Learning, took a number of photographs of the fish, some of which are shown herewith, to give a graphic idea of its appearance and unfish-like movements (Figs. 3 to 6). In side view, Fig. 3, the fish is shown in a position of rest, its body resting upon the bottom, its long, paired extremities extended out, braced against the glass side of the aquarium. When moving, however, the fish would lift its body by means of the paired fins, and these would then serve after the fashion of the arms and legs of a quadruped as the fish 'walked' slowly about, alternating the forward and backward movements of its extremities. This condition is illustrated in Fig. 4, in which the bend of the arms and legs, where they support the weight of the fish is shown satisfactorily. In this figure, which, together with Figures 5 and 6, were photographed from almost directly above the fish, one observes that the strain upon the limbs falls, not upon their

Fig. 4.
Fig. 5. Fig. 6.
Lung-fish showing Various Movements.

tips, but near the middle. Thus one notes in Fig. 6 that the tip of the right-hand pelvic limb curls upward and is free from the bottom. One observes especially in Fig. 3 the stress upon the left pectoral limb, which causes it to be bent almost at right angles in an elbow-like fashion. This limb, by the way, has lost its tip, and is being regenerated, the lighter portion, as shown in the figure, having already been grown. I might note that at the point where the injury occurred a small transverse branch later made its appearance, but after this had grown for a year or two and become one eighth of an inch in diameter, it gradually degenerated and finally entirely disappeared. A characteristic movement is illustrated in Fig. 5; here the fish, having reached the end of the tank, draws back before turning in another direction. To accomplish this result, the fins again operate in a quadrupedal fashion: pressing on the limbs firmly, the fish recoils, pushing itself back by means of its shoulder and pelvic muscles, the tail and body taking little or no part in the process. In this figure we again note the strain which is laid upon an extremity, for the left arm is bent almost to the shoulder.

Another characteristic movement is pictured in Fig. 6, where the animal is circling around. The weight of the hinder body is supported firmly by the outstretched legs, and the arms swing forward and backward, turning the anterior part of the body. In the present position the animal is on the point of again advancing, and in this event the limbs will move alternately as shown in Fig. 4. Throughout these varied movements the fish is slow and deliberate, reminding one rather of a newt than of a fish. In the present figures attention should be called to the great length of the uninjured arm, which in this small specimen indicates doubtless a larval feature of the fish. Also noteworthy is the position of the external gills, which stand out at the sides of the head very much as they do in a larval salamander.

From this stage onward the life of the lung-fish was a rather uneventful one. It received its daily diet of earthworms with apparent relish, and upon them it thrived and grew. Its yearly increase in size varied between two and three inches; at the time of its death it measured eighteen inches. Its movements in the aquarium were like those of larval salamanders, axolotl, for example. Only on rare occasions did it swim in a fish-like manner by means of caudal fin and undulating body, and only twice a year did it show of what sudden movements and great activity it was capable. On these occasions it was taken from the tank and carried to or from the New York Aquarium where, through the courtesy of the officials, it was kept during the summer. Cold weather, as might be inferred, it was least capable of enduring. On several occasions during winters, when the temperature in the aquarium room became less than 50° F., the fish was found in a semi-torpid condition. It was then taken out and handled with scarcely a movement, but was revived by immersion in warm water. It gave its attendant no uneasiness on the score of appetite, for it took its food with clock-like regularity. Its great difficulty, however, appeared to be due to defective eyesight, for even though a moving worm were put in its immediate neighborhood, the fish did not appear to detect its presence through the sense of sight. At first, stimulated probably through its lateral line system, the fish seemed to feel the movements of the earthworm; it would then turn in the direction of the food, move towards it with apparently increasing enthusiasm, but when only at close range did it seem actually to see the prey. The fish's movements in feeding reminded one rather of a turtle than of a fish, or, best of all, of its kindred salamanders. Eyeing the moving worm steadily, it would make a sharp snap at it. If this movement failed, it would appear to deliberate, gaze fixedly at the object, and snap again. If more successful this time, it would pause with the food in its mouth, then with a series of accelerating snaps, the entire worm would be ingested. Occasionally a worm would be cut entirely in two by the quick snap of the fish's powerful jaws, and this would result in the

Fig. 7 a. Fig. 7 b. Fig. 7 c.

loss of the worm and in the feeding beginning anew. During this entire process the fish's arms would be spread widely apart, so as to support the weight of the head.

In later years the fish became quite tame, and would feed out of the hand of the laboratory attendant, who always maintained that the fish distinguished him from other visitors. Certain it was that he finally accustomed the fish to a diet of raw meat, and this substitute for earthworms proved a convenient one during the cold season. A finger thrust into the aquarium and stirred vigorously would be enough to attract the fish's rather sluggish attention: it would slowly leave its resting place, 'walk' toward the region of the disturbance, rise to the surface and after giving the usual evidence of bad eyesight would finally get its mouthful of food. The fecal material of the fish, one might mention, showed the cast of the spiral intestinal valve which in lung-fishes is almost as well developed as in sharks. Possibly, therefore, some of the coprolites from early geological horizons which have generally been referred to sharks may have belonged to contemporary lung-fishes. The fecal material at the time it is deposited appears as in Fig. 7a; after remaining in the water for several hours it presents the appearance 7b, and finally, after twenty-four hours, uncoils as in Fig. 7c.

The air-breathing movements of the fish were irregular. At times it would come to the surface about every five minutes and swallow a mouthful of air; then again several times this period would elapse before the fish would rise to the surface. In all cases escaping air passed out through the gill clefts, usually through those on the left side.

  1. The lung-fish is generally regarded as a little modified survivor of the ancient 'connecting link' between the water-living fishes and the air-breathing and four-legged amphibians. There is the clearest evidence that in the early geological periods the lung-fishes represented a flourishing stock both in numbers and kinds. At the present day they are reduced to three genera, one Australian^ one South American, and one African.