Page:Popular Science Monthly Volume 60.djvu/515

Rh closely those of the Rhine according to a recent and very thorough investigation by the Fishery Board of that country. The salmon in the rivers of Alaska, however, acccordingaccording [sic] to the report upon the subject by the United States Fish Commission, exhibit certain differences which are significant of the physiological purpose of the habits and tissue changes in the breeding salmon. The principal runs of these salmon from the sea to their spawning grounds occur after the ice has broken up, and through a great part of the brief Alaskan summer. The number of fish swimming up stream at such times is so enormous that at places the current is almost choked by the struggling mass. A man wading through the shallows can kick the salmon out upon the shore by scores. The distances which these salmon must ascend is much less than in the Rhine—often only a few miles. Yet the difficulties overcome in struggling over shoals, leaping up waterfalls, and in attempting to pass the barriers of heavy timber recently erected by the canneries, are enormous. During this journey the males develop formidable looking beaks, and the genitalia grow to a size even greater perhaps than do those of the Rhine salmon—although exact figures are not available. At the same time both sexes become emaciated to an extreme degree, all the muscles and organs of the body being drawn upon apparently to supply material to the genitalia. It is certain that the fish do not feed after leaving salt water; indeed it is doubtful whether the beaks of the males would allow it even if they wished. But all the Alaska salmon—of which there are several species—differ from those of the Rhine in one respect. No adult salmon has ever been seen swimming down stream, and those which are washed down by the current die after reaching salt water. The greater number after spawning remain, near the spot where the eggs are deposited, driving off intruding salmon that would disturb their nests, and marauding trout that would devour their eggs, until overcome by starvation and the exhaustion entailed by their journey and tissue changes, they die. They afford a striking example certainly of the sacrifice of the individual to the good—or the only 'good' that Nature seems to recognize—the perpetuation of the species; and this example is none the less striking because it can scarcely be supposed that these fish have any consciousness of the object for which they thus struggle and die.

The reason for these habits and tissue changes is probably to be found in. the advantages which they confer upon the salmon in the