Page:Popular Science Monthly Volume 18.djvu/226

214 the sea seeming to be essential to the ripening of the ova—a property which makes the study of the procreative functions of this fish more difficult. The tunny lives exclusively in the sea, but goes to the coasts of the Mediterranean, particularly to Sicily and Sardinia, to spawn. The sea graylings ascend the rivers of Spain and France in such numbers that the water seems covered with them.

The journeys of the fish in returning from their spawning-places after spawning are seldom performed in masses, but individually and in small groups. The fish, which went up fat and in fine condition and flavor, are exhausted, lean, and weak. Not much is known of the migrations of other fish than the salmon during these journeys, for the fishermen pay little attention to them and they therefore seldom come under the observation of science.

Next in order of the migrations are those of the young brood from their spawning-places. The young herring do not as a rule remain longer than four or five months where they are hatched. They then go down to the sea while the young eels go from the sea up to the rivers after about the same time. The young herring are observed with difficulty, for it requires a skilled eye to perceive their minute, transparent bodies in water that is in any degree disturbed; but in perfectly still water the schools may be seen moving to and fro like fine flecks of cloud. The salmon remain a full year in the mountain-streams, and do not go down to the sea till they have become a vigorous, greedy fish of about a finger's length.

Journeys in search of food are not periodical or regular, like the previous migrations, or are only incidentally so. The most important of them and the nearest to being periodical are the visits of the codfish to Newfoundland and the Loffoden Islands, concerning which it is as yet not certain whether they may not be partly connected with purposes of reproduction. Schools of other smaller fishes appear along with the cod, a salmonid, the herring, and a number of squids, which are all alike used by the fisherman as bait. The migrations of the predatory fish which follow the other fish in their spawning-journeys naturally partake of the periodical character of those journeys; the fish that pursue the herring follow them into the farthermost corners of the bays to which they resort.

The autumnal visits of mackerel to the Gulf of Kiel are of particular interest. They do not take place every year, and are not often marked by very great numbers, but they have attracted attention since 1624, when they were described by Schonevelde, on account of the peculiar character of the food that attracts the fish. The Gulf of Kiel is visited in August and September by great numbers of the Medusa aurita, which fill its waters, perform their reproductive duties, and perish on its shores, leaving hardly a trace of their watery tissues behind. In their maws swarm numerous individuals of a moderately large parasitic crab, and it is for the sake of these that the mackerel