Fish

a vertebrate animal living in water only. In place of lungs a fish has delicate fring-like gills in slits at the side of its neck. The blood courses through the gills as it does through ordinary lungs, and through the thin walls of the gills it absorbs the air that is mixed with the water. Ordinarily a fish cannot live in air. Its gills dry up and, strange to say, the fish dies for want of air. An exception to this statement must be made in favor of one fish, the climbing perch of India, which is able, it is said, to carry water in cells with which to moisten its gills. It is able to leave its pond for two or three days, and is exhibited by the jugglers of India and China as a "fish out of water." Nor can a fish live without a constant supply of air. Unless the water is kept fresh, that is, supplied with pure air, a fish dies. Ponds are sometimes frozen over so closely that all the fishes die for want of air. Air holes in ice are frequently crowded by fishes struggling for water that has fresh air in it. Fishes take in water through the mouth and force it out through the gills. If a fish be held head down stream, or if in any way water be forced through the gills and out of its mouth, it will drown, just as a person would drown from too much water on the lungs. The heart of a fish has one auricle and one ventricle. The circulation of its blood is slow and the blood is cold.

The body of a fish is shaped for easy passage through the water. Boat builders have spent much time studying the form, "lines," of various fishes with a view to secure speedy models. The feet and tail of a fish are fitted for swimming. The front feet are converted into pectoral fins; the rear feet into ventral fins; the tail into a caudal fin; in addition to which a fish may have a dorsal or back fin or two, and an anal fin. A fin consists of a thin membrane spread on or supported by rays. The presence or absence, shape, and position of these fins is of service in the classification of fishes. The motion of a fish is derived chiefly from a flip of its tail; the dorsal and ventral fins serve to balance the body, and the front or pectoral fins are spread to arrest progress at any time. The scales are outgrowths of the skin and point backward. Each scale is to be regarded as a lock of hair imbedded in glue. Certain scales arranged in a line on each side of the fish are pierced with tubes through which a slimy matter oozes that serves to lubricate the body and make it slippery. The scales are exceedingly variable, and are another guide in classification. The catfish has no scales.

Fishes are supposed to see well for short distances, to hear tolerably well, and to have a fairly acute sense of smell. It is thought they have little sense of taste or little sense of touch, save in the feelers with which some fishes are provided. Most fishes are flesh eaters, preying on flies, water insects crayfish, snails, frogs, and especially young fishes, or fishes smaller than themselves. Nature seems to have provided the small fishes for the benefit of the larger ones.

The catching of fish is an occupation employing a large number of persons. Fishes are taken with the hook, the spear, the trap, and with nets. Fishes furnish a considerable portion of the food of mankind, and are a source of wealth to many nations. Angling is one of the most delightful of diversions, even though Dr. Johnson did define an angler as "a pole and line with a fool at one end and a worm at the other."

Recent authorities state that the number of different kinds of fishes in the world, not counting fossil species, is about 12,000. Of this total, there are 3,263 species in North America. The cod is the most valuable American fish. The salmon ranks next.

The fishes of North America may be placed in nineteen groups:

1. The spiny-finned fishes, including the bass, sunfish, perch, bluefish, mackerel, tuna, mullet, and swordfish.

2. The pikes, including the muskallunge and pickerel.

3. The trout, including the salmon, tarpon, shad, whitefish, and herring.

4. The flying fishes.

5. The solid-jaw fishes.

6. The suckers, including buffalo fish, carp, and minnows.

7. The catfishes, including the bullhead.

8. The sticklebacks.

9. The common halibut.

10. The angler.

11. The eeles.

12. The pipe-fishes.

13. The dogfish.

14. The gar-fishes.

15. The sturgeons.

16. The paddle-fish.

17. The chimeras.

18. The sharks.

19. The rays.

See Fishery; also articles on the several fishes.