CHAPTER IV

FISHES

89. What is a fish?"A fish is a backboned animal which lives in the water and cannot ever live very long anywhere else. Its ancestors have always dwelt in water, and likely its descendants will forever follow their example. So, as the

water is a region very different from the fields or the woods, a fish in form and structure must be quite unlike all the beasts and birds that walk or creep or fly above ground, breathing air, and being fitted to live in it. There are a

great many kinds of animals called fishes, but in this all of them agree: all have some sort of a backbone, all of them breathe their life long by means of gills, and none have fingers or toes with which to creep about on land.”1

90. The regions and appendages of a yellow perch. Study Figure 90 and notice that the body of the yellow perch is divided into three regions; namely, head, trunk, and tail. Unlike the body of many animals, no neck is present, and the head, therefore, is joined directly to the trunk. The line of union of head and trunk is the posterior 2 margin of movable flaps, called the gill covers, on the sides of the head. Just behind or posterior to the gill cover on each side of the trunk of the fish is a paddle-like organ called the pectoral fin. On the ventral surface, below the pectoral fins, is a second pair which are known as the pelvic fins. The pectoral and pelvic fins are together known as the paired fins of the fish. Besides these this animal has several unpaired fins, which we shall now locate. On the dorsal surface notice two dorsal fins, one behind the other, which project upward. Below the posterior dorsal fin, on the ventral surface, is another single fin called the anal fin. The tail region is considered to begin just in front of the anal fin, since in the fish the body cavity that contains the important organs of digestion, circulation, and reproduction ends at this point (Fig. 98). The anal fin, therefore, and also most of the posterior dorsal fin, are attached to the tail region. At the posterior end of this third region is the broad forked tail fin.

91. Regions and appendages of a goldfish. -Laboratory study.

1 Jordan's "Guide to the Study of Fishes," Vol. I, p. 3.
"The meaning of each of these terms is explained in 6.

Materials: A living goldfish in a battery jar for each two students. Goldfish may be kept indefinitely in a glass jar with green water plants; the latter supply the fish with food and oxygen. Perch, and if possible the heads of large fishes like the cod, should be obtained, preserved in formalin (5 per cent), and then thoroughly washed in running water for twenty-four hours before they are used; material treated in this way loses its fishy smell, and may be kept in the formalin solution year after year. A fish skeleton is also needed for demonstration. The Jung charts of the external and internal structure of the perch are useful.

Observe a living goldfish and compare it with Figure 90. 1. Name the regions of its body and state, with reference to gill cover and fins, where each region begins and ends. 2. Name and locate all the organs you find on the head. 3. What paired and what unpaired fins are found on the trunk? Using the terms anterior, posterior, dorsal, ventral, median, and lateral, locate each of these fins.. 4. Name and locate the fins attached to the tail region of

the body.

5. Make an outline sketch about five

inches long of the side view of a
living goldfish to show the shape
and relative size of the three re-
gions, the position and shape of the
organs of the head and of the
various kinds of fins. Label the
regions and the organs that you
have drawn, in a manner similar to
Figure 90.

92. Some differences in the form of fishes.

-One can usually tell whether or not an

animal is a fish; but in some cases this is FIG. 91.-Sea horse.

extremely difficult. Who would think, for instance, that such animals as the sea horse (Fig. 91) and the pipefish (Fig. 92) would be

FIG. 92. Pipefish.

classed with the perch and goldfish? Yet such is the case, since careful study has shown that these forms have all the charac teristics mentioned in 89.

It is evident that the goldfish and perch have bodies that are considerably longer than they are wide or deep, and this is true of most of the common fishes. In the group of fishes known as the eels,

this elongation is so marked that they look more like snakes than they do like fishes. But the eels are not the only fishes that show a striking development in one dimension. The flounders, for example (Fig. 93), exhibit a notable growth in a dorso-ventral direc

FIG. 94.-Sting ray. (Jordan and Evermann. Courtesy of Doubleday, Page & Co.)

tion. So far has this been carried that the fish is unable to retain a vertical position, and consequently lies on one of its sides. The eyes, which, in very young flounders, are situated like those of the goldfish n either side of the head, by a twisting of the bones of the

skull, both come to lie on the same side of the head. Otherwise, as may be seen, one of the eyes would rest on the sand or mud, when the animal is on the sea bottom. Fishes like the skates and sting rays (Fig. 94) have also a much flattened body, but these animals have