| It will be wise to learn something about fishes and | | | | vertebral column or "backbone", with a very |
| their requirements if you plan on setting up an | | | | complicated skull at the front end; behind the skull |
| aquarium. | | | | there are shoulder-bones supporting a pair of pectoral |
| Breathing | | | | fins, corresponding to our arms, and beneath the |
| Fish take in water through the mouth; they do not | | | | abdomen there is a pair of pelvic fins supported by |
| drink it, however, but pass it out backwards through | | | | internal bones, representing our legs. |
| the gill-openings at the sides of the head, under the | | | | The latter are sometimes called ventral fins, but this |
| bony gill-covers. As it goes through it bathes the gills, | | | | is not a good name, because the word ventral, when |
| which are so constructed that they can take oxygen | | | | applied to fishes, means on the lower side of the |
| out of the water and get rid of carbon dioxide in | | | | body, and can be applied also to the anal fin, which |
| exchange. The gills, then, are their breathing organs; | | | | lies below the tail, and is single. On the back, in the |
| they have no lungs. But the process of breathing is | | | | middle line of the body, is the dorsal fin, sometimes in |
| otherwise much like ours, and if there is not a proper | | | | two parts. At the end of the tail is the caudal fin; this |
| supply of oxygen in the water, they will sicken and | | | | is often called "the tail" by non-aquarists, but should |
| die. | | | | at the worst be called the "tail-fin". |
| The oxygen is dissolved in the water, and the carbon | | | | Senses |
| dioxide given off, through contact with the air at the | | | | A fish is provided with a brain, simpler than ours, but |
| surface. | | | | nevertheless more efficient than some people realize; |
| Thus it will be understood that if the surface area is | | | | it displays intelligence, and is capable of learning. It has |
| too small the water will become charged with carbon | | | | good eyes and a keen sense of smell. The general |
| dioxide, and there will not be room for replacement | | | | plan of the nervous system is similar to ours, though |
| of the oxygen when it is used by the fish. | | | | again less complex, and it is well to remember that a |
| The oxygen that the fish breathes is passed into the | | | | fish feels pain and may be shocked. Tapping on the |
| blood circulatory system, and so to the tissues, | | | | glass, or sudden knocks on the frame of the |
| where it is eventually combined with elements of the | | | | aquarium, should be avoided, for it has a very |
| digested food for the production of energy and | | | | startling effect on the fishes. |
| growth (metabolism). The results of this combination | | | | Along the side of a fish is a series of very sensitive |
| are largely carbon dioxide and water, which have to | | | | organs, which are usually visible as a line formed by |
| be eliminated. The former is breathed out, and the | | | | tubes in the scales. This is the lateral line, which in |
| latter excreted by way of the kidneys. This is all | | | | effect is the outer ear of the fish. It is sensitive to |
| much the same as the process in higher animals, | | | | pressure-waves and vibrations in the surrounding |
| including ourselves, for the organization of the body | | | | water, and conveys them to the brain. There is an |
| of a fish is very similar to ours, though a little simpler. | | | | inner ear surprisingly like our own, but concerned |
| Fins | | | | mainly with balance, so far as we can tell. |
| Fish are the lowest true vertebrates, and therefore | | | | There is of course much more that can be learned |
| can be compared with our earliest ancestors. They | | | | about fish, but this information will get you off to a |
| have a bony skeleton, consisting of a jointed | | | | very good start. |