Laboratory exercise.—Study of a living fish—adaptations for protection, locomotion, food getting, etc.
Laboratory demonstration.—The development of the fish or frog egg.
Visit to the aquarium.—Study of adaptations, economic uses of fishes, artificial propagation of fishes.
Two Methods of Breathing in Vertebrates.—Vertebrate animals have at least two methods of getting their oxygen. In other respects their life processes are nearly similar. Of all vertebrates fishes are the only ones fitted to breathe all their lives under water. Other vertebrates are provided with lungs and take their oxygen directly from the air.[32] We will next take up the study of a fish to see how it is fitted for its life in the water.
study of a fish
The Body.—One of our common fresh-water fish is the bream, or golden shiner. The body of the bream runs insensibly into the head, the neck being absent. The long, narrow body with its smooth surface fits the fish admirably for its life in the water. Certain cells in the skin secrete mucus or slime, another adaptation. The position of the scales, overlapping in a backward direction, is yet another adaptation which aids in passing through the water. Its color, olive above and bright silver and gold below, is protective. Can you see how?
The bream. A, dorsal fin; B, caudal fin; C, anal fin; D, pelvic fin; E, pectoral fin.
The Appendages and their Uses.—The appendages of the fish consist of paired and unpaired fins. The paired fins are four in number, and are believed to correspond in position and structure with the paired limbs of a man. Note the illustration above and locate the paired pectoral and pelvic fins. (These are so called because they are attached to the bones forming the pectoral and pelvic girdles. See page [268].) Find, by comparison with the Figure, the dorsal, anal, and caudal fins. How many unpaired fins are there?
The flattened, muscular body of the fish, tapering toward the caudal fin, is moved from side to side with an undulating motion which results in the forward movement of the fish. This movement is almost identical with that of an oar in sculling a boat. Turning movements are brought about by use of the lateral fins in much the same way as a boat is turned. We notice the dorsal and other single fins are evidently useful in balancing and steering.