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