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