The Encyclopedia Americana (1920)/Fishes, Nest-making by
FISHES, Nest-making by. While the great majority of fishes cast their eggs (spawn) and the fertilizing milt of the males loose in the water, many follow a much less wasteful method, even taking good care of them and of the resulting fry. All who have had experience with aquariums know of this habit in the little sticklebacks, the males of which construct, in crevices of rocks, or among water-weeds, elaborate muff-shaped nests of small sticks and plant-fragments, woven together with glutinous threads spun from an organ connected with the kidneys. In such a nest the female then deposits her few and relatively large eggs, which are zealously watched and brooded by her fierce little mate. This case is nearly paralleled by some of the European gobies; and also by that curiosity of mid-ocean, the Sargasse-fish, which spends most of its life resting upon the floating gulf-weed of the sea. Here it glues together, by means of a pasty secretion from its body, the twigs and leaves of a single plant of the gulfweed (Sargassum) into a sort of bag, within which large numbers of eggs are hung by silky fibres like clusters of grapes. Somewhat similar is the precaution of the gouramis and paradise-fish of Oriental waters, which form a floating raft of bubbles of air and mucus blown from their mouths, in which the eggs are entangled and float about guarded by the male. Another sort of floating nest, composed of bits of weed, is constructed as a raft for its thousand or more eggs by one of the great mormyrs (Mormyrus) of the Nile and its tributaries. This is a big, strange-looking, beaked fish related to the pike, and representing a group (Scyphophori) venerated by a sect of the ancient Egyptians and depicted on their monuments. Its nests are carefully avoided by the negroes, for the fish will attack anything that approaches its property, and it can bite cruelly.
Most of the nest-builders are fresh-water fish, and represent a variety of groups. The habit is familiar to us, indeed, in the case of our bass and sun-fish. As soon in early summer as the water is suitably warm the male black bass (of both species) betakes himself to the shallow margin of the river or pond, where he lives, where the bottom is sandy, or better, is covered with small pebbles. There he scoops out with nose and fins a saucer-like depression, into the centre of which he pushes a layer of little stones. Having prepared the place to his satisfaction, he searches for a female bass who is “ripe,” as they say — that is, carrying eggs sufficiently matured for extrusion. Others do not attract him; or his attentive addresses may be repulsed. Having discovered a female ready to spawn he appeals to her by such affectionate inducements as fishes understand, and endeavors to lead her to the home he has prepared. She may be reluctant and coy, but he persistently entices her until together they halt above the plate of pebbles, which he now cleans anew by his waving fins. Often he will sidle up to her, and, pressing against her body, will appear to try to assist her in discharging her eggs; and as soon as this discharge begins he supplies the milt that contains the fertilizing element necessary to their development. This done she goes her way without further attention from him. Henceforth his interest is solely in the eggs that have fallen among the pebbles, and he never leaves them for more than a minute or two, fanning them steadily as he poises above the nest, and watching that no big water-beetle, or crayfish, or predatory minnow invades his domain. It is comical to see the fierce anger with which he will dash at any fish that ventures near, and when, as frequently happens, a dozen or so bass are nesting within a yard or two of one another, everyone fearful of his neighbor, vigilance and courage are called for every instant. This care extends to the fry after the eggs hatch, until they have grown somewhat, after which they are more in danger of being eaten by their parent than by anything else. Many other fishes show this fatherly zeal.
Sunfish have similar habits, but they seek places for their nests more sheltered by vegetation, they are less quarrelsome and their tendency to cannibalism is far less.
Some fishes, however, carry this building of pebble-nests to greater perfection. One of these is our common little black-nosed dace (Rhinichthys atronasus), which clears a space, puts a layer of stones, then a layer of eggs, then layer of pebbles, and so on until the laying is finished. Both sexes work together, bringing the pebbles in their mouths. In deeper rivers the lamprey eels (Petronyzon) do something similar, and are known as “stone-toters.” A silurid (Arius) of Australia makes mounds of alternate layers of stones and eggs; and those brilliant sea-fish, the wrasses, are even more industrious, for a pair, working together, will form a nest of sea-weeds, broken shells, corals, etc., in which their eggs safely hatch. That strange little fish of the rivers of the Mississippi Valley, the bowfin, or grindle (Amia calva), which is so interesting as a survivor of a race that almost became extinct in the early ages, digs in the mud of sluggish streams an excavation two or three feet in diameter, and several inches deep, which is garnished all around the edge with bits of plant-roots or perhaps a ridge of sand. This done he awaits the coming of a female, not often seeking one; for some Lady Bowfin presently comes along, and the pair consort for a considerable time, followed by spawning, after which the male guards the eggs that stick in great numbers to the bordering weeds and rootlets. Very similar care is shown by a larger relative in West Africa (Protopterus) which removes all the grass from a wide space of bottom, thus made perfectly smooth and walled in by the debris swept out of it. Here the eggs are dropped on the bare mud. “Until the eggs are hatched, which occurs about the eighth day, and while the larvæ are in the nest, the male remains on guard, and is apt to bite severely an incautious intruder. Probably with a view to aërating the eggs, the water is continually lashed about by the tail of the guardian parent.” A fish of Gambia (Heterotis) attends to the security of its eggs in the same way. Several kinds of fishes hide their eggs in natural or artificial cavities. Thus some British blennies attach them in a single layer to the sides of cavities in rocks or among stones, where they are watched by the male parent. The little male European sand-goby scoops out the sand from beneath an empty shell, usually that of a scallop, whereupon a female deposits her adhesive eggs on the under surface of the shell and leaves the male on guard. Several kinds of catfish stow away their spawn in crevices of a steep bank, or even dig a burrow into the bank, as is done by our common bullhead. Certain South American silurids even line the excavation with grass or leaves amid which the eggs are hidden. All these deposits are guarded. That this guardianship all over the world is the office of the males alone, whatever the character of the fish, is notable; and also that in all such cases he continually agitates the water about the nest, which is precisely what fish-culturists have found it necessary to do in their troughs and jars, when they attempt to hatch fish-eggs artificially.