Friedrich Heincke

“ The eel is the only European fish which goes from fresh water to the sea to spawn. Its journeys take place some time before the fish are ready to spawn, an abode in 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. ”

“ Hence it is necessary for the eggs to be laid in well-ventilated waters. This is impossible if they are spawned in deep water, where they will sink away below the reach of atmospheric movements. They must be deposited in waters that are disturbed to the bottom. Such waters are the shallows near the shore, where the herring lay their eggs, and the living streams, which are the resorts of the salmon and sturgeon. The fish, impelled at spawning-time to go in the direction of the most air, keep on till they find it in the places best suited for breeding. ”

“ The resort of the fish to the same place is repeated every year with a wonderful regularity. The appearance of the herring in Norway varies at most not more than fourteen days. The energy of the movements, is remarkable. The salmon, traveling from the sea to its spawning-places, surmounts considerable difficulties, leaping up to the tops of falls several feet high, and repeating its jumps if it fails at first, till it succeeds. ”

“ 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. ”

“ Different species of fish require different amounts of oxygen, the same as different animals do. The salmon and trout need much, and for it seek those waters which have the liveliest motion—mountain-streams. The opinion that these waters are more favorable to the development of the eggs because they are fresh is based on erroneous premises. Many of the species that commonly go to fresh waters also lay their eggs in salt waters, and even salmon sometimes lay them in the sea. ”

“ Other formidable fish, unsocial in their habits, being scattered over the ocean, are less accessible to science.
When more than the usual number of fish go up to spawn, the number of fish pursuing them is likely to be also increased. It sometimes happens thus, that species of fish which have not commonly followed, the schools are attracted to them by the extraordinary abundance of food, and find their way to places where they were before unknown. Many fish are found in opposite quarters of the globe. ”

“ Migrations may also be performed under the influence of circumstances not connected with reproduction or the search for food. It is not certain whether fish are ever' driven from their homes by a cooling of the water. Removals from such a cause would not take place in large masses, and might easily escape observation. As a rule, fish are not sensitive to changes of temperature, and can endure the greatest diversities provided they have food enough. Certain tropical fishes have a remarkable faculty of performing journeys by land. ”

“ The climbing fish and an ophiocephalus of the East Indies and the Doras costatus of South America are able, when the ponds and swamps in which they live are dried up, to travel for several hours over the land to find places affording more water. The eel has been said to travel for considerable distances from one pond to another. It is certain that eels are able to live for a considerable time out of the water, and, though the fact has not been scientifically established, there is no reason to doubt that they can travel. ”

“ Thus every fish illustrates in some way the law that a constant change of air is essential to the development of its eggs. Agitated and sun-lighted waters are also most favorable to the larvæ of crustaceans and mollusks, of echini and polyps, and to the microscopic creatures of which the food of the fry chiefly consists, and thus fulfill another condition of the most vigorous growth of the young fish.—Translated and abridged from Die Natur. ”

“ Salt water really appears, from the most recent researches, to contain—other conditions being the same—more air than fresh. The same cause which impels the salmon to ascend to the lively, fully aërated streams of the mountains attracts other fishes from the deep seas to the shallows and rivers, and the eel from the bottoms of still-water ponds to the wind-disturbed waters of the bays. ”

“ Inasmuch as migrations may often lead to a permanent enlargement of the domain of certain species, a knowledge of the laws and circumstances by which they are influenced has an important bearing on the study of the geographical distribution of species. ”

“ The agitation is caused by the schools of herring, which are so closely packed that a boat can not pass through them, an oar may be made to stand up among them, and they may be dipped up in buckets or caught with the hand by the thousand. ”