“And God said, Let the waters bring forth abundantly the moving creature that hath life. . . . And God created great whales and every living creature that moveth, which the waters brought forth abundantly, after their kind. . .and God saw that it was good.
And God blessed them, saying, Be fruitful and multiply, and fill the waters in the seas.”
To and fro with gracefulness and ease swim the fish, remarkably adapted to its environment. We marvel at its perfect freedom in the lake or stream as it flits up and down with such rapidity and skill. What a transformation there is when we take this creature from its normal surroundings! How helpless and lifeless it soon becomes as it flounders pitifully on dry land, for was it not created to be in water?
We ask ourselves the question, Why does its freedom depend on its being in water? By examining the fish’s body we find the solution. Most animals are equipped with lungs which enable them to breathe air directly; not so with fish, for they must obtain their air from the water by means of gills. These comb or rake-like structures have many small fingerlike tines called filaments which are richly supplied with tiny blood vessels giving off the waste carbon dioxide into the water and removing the fresh oxygen from it. After the water enters the mouth, it flows over the gills and out of the operculum (external opening on lower side of the head). It is this constant flow of water that separates these tiny filaments; thus, the maximum surface is exposed which enables the constant exchange of oxygen and carbon dioxide — essential to life. As soon as a fish is removed from water, these filaments adhere to each other and become covered with a sticky substance, which prevents breathing. Even though the fish may be surrounded with an abundance of air, it cannot breathe.
However, there is a certain family of fish which inhabit Lake Chad in Africa, which is an exception to the rule that fish always breath by means of gills. During the dry season, much of the lake dries up leaving many of these fish stranded. Instinctively, these creatures make mud huts for themselves and live in these until once again the lake becomes its original size. During the interval when the lake has receded, the fish breathes by means of its “swim bladder” or float, which in this species of fish is connected with the outside, and functions as a lung.
The fish possesses the external sense organs, namely: nostrils, eyes, and the lateral line. The two nostrils of the fish are peculiar in that they are U shaped tubes, each having two external openings. Although they are not useful for breathing, they are essential in distinguishing various odors in the water as the water passes thru these tubes. Just posterior to the eye and on each side of the body, one finds a darkened lateral line extending to the tail. This makes it possible for the fish to register changes in pressure and other movements in the water. Therefore, although the fish lacks ears, the lateral line functions as an auditory organ.
Another feature which adapts the fish to water is the swim bladder or float. Within the body cavity attached to the. backbone is this thin-walled, air-filled, balloon-like structure. By means of it the fish can voluntarily elevate or lower itself in that water, regulated by the amount of air expelled from it, thus functioning as a ballast tank in a submarine.
If we were to do some deep-sea diving, we would discover a host of interesting and unusual forms which inhabit the watery depths and ocean bottoms. It is rather astonishing how animals can continue to exist in an abode of utter darkness, for no sunlight can penetrate to such a depth. The factor of extreme pressure exerted on their bodies makes it remarkable that life can go on. Often there is no plant life available. Then, too, we would find that, some of these species of fish are seemingly handicapped by blindness, and those having eyes are thought to see by means of phosphorescent light cast from the bodies of many of these animals. Examination has proved that certain fluids within the tissues of the fish make it possible for them to resist the pressure forced upon them. They possess sensitive organs of touch and their jaw and teeth are larger to offset the fact of their blindness in capturing food.
There are many other interesting facts about these “inhabitants of the sea,” which may be discussed in another issue.