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