Fig. 122.—Portuguese Man-of-war Fish, Gobiomorus gronovii. Family Stromateidæ.
Migratory Fishes.—The movements of migratory fishes are mainly controlled by the impulse of reproduction. Some pelagic fishes, especially those of the mackerel and flying-fish families, swim long distances to a region favorable for the deposition of spawn. Others pursue for equal distances the schools of menhaden or other fishes which serve as their prey. Some species are known mainly in the waters they make their breeding homes, as in Cuba, Southern California, Hawaii, or Japan, the individuals being scattered at other times through the wide seas.
Anadromous Fishes.—Many fresh-water fishes, as trout and suckers, forsake the large streams in the spring, ascending the small brooks where their young can be reared in greater safety. Still others, known as anadromous fishes, feed and mature in the sea, but ascend the rivers as the impulse of reproduction grows strong. Among such fishes are the salmon, shad, alewife, sturgeon, and striped bass in American waters. The most remarkable case of the anadromous instinct is found in the king salmon or quinnat (Oncorhynchus tschawytscha) of the Pacific Coast. This great fish spawns in November, at the age of four years and an average weight of twenty-two pounds. In the Columbia River it begins running with the spring freshets in March and April. It spends the whole summer, without feeding, in the ascent of the river. By autumn the individuals have reached the mountain streams of Idaho, greatly changed in appearance, discolored, worn, and distorted. The male is humpbacked, with sunken scales, and greatly enlarged, hooked, bent, or twisted jaws, with enlarged dog-like teeth. On reaching the spawning beds, which may be a thousand miles from the sea in the Columbia, over two thousand in the Yukon, the female deposits her eggs in the gravel of some shallow brook. The male covers them and scrapes the gravel over them. The female salmon does as much as the male in covering the eggs. Then both male and female drift tail foremost helplessly down the stream; none, so far as certainly known, ever survive the reproductive act. The same habits are found in the five other species of salmon in the Pacific, but in most cases the individuals do not start so early nor run so far. The blue-back salmon or redfish, however, does not fall far short in these regards. The salmon of the Atlantic has a similar habit, but the distance traveled is everywhere much less, and most of the hook-jawed males drop down to the sea and survive to repeat the acts of reproduction.
Fig. 123.—Tide-pools of Misaki. The Misaki Biological Station, from the north side.
Catadromous fishes, as the true eel (Anguilla), reverse this order, feeding in the rivers and brackish estuaries, apparently finding their usual spawning-ground in the sea.
Fig. 124.—Squaw-fish, Ptychocheilus oregonensis (Richardson). Columbia River.
Pugnacity of Fishes.—Some fishes are very pugnacious, always ready for a quarrel with their own kind. The sticklebacks show this disposition, especially the males. In Hawaii the natives take advantage of this trait to catch the Uu (Myripristis murdjan), a bright crimson-colored fish found in those waters. The species lives in crevices in lava rocks. Catching a live one, the fishermen suspend it by a string in front of the rocks. It remains there with spread fins and flashing scales, and the others come out to fight it, when all are drawn to the surface by a concealed net. Another decoy is substituted and the trick is repeated until the showy and quarrelsome fishes are all secured.