great flocks and move regularly to and from the shore, as does that species. It nests in trees, preferring pines. A similar but somewhat smaller and blacker species (Corvus minutus) inhabits Cuba. Compare Crow.
FISH CULTURE, or Pisciculture (from Lat. piscis, fish + cultura, culture, from colere, to cultivate). The breeding, rearing, transplanting, and protection of aquatic animals in order to maintain or increase their abundance. Literally the term applies only to the culture of fishes, but it is loosely used to include also such forms as the lobster, oyster, frog, etc.
General Considerations. The maintenance of artificial ponds for the rearing of fresh-water fishes for food or ornamental purposes is a very ancient practice, and is carried on by nearly every civilized nation. In China fish culture has been extensively practiced from ancient times. In Europe, and particularly in Germany and Sweden, pond culture is of considerable importance. In recent years, however, fish culture has become almost synonymous with the harvesting of eggs, their artificial fecundation, and the rearing of the young up to varying stages in hatcheries established for that purpose. This seems to have been an ancient custom in China, where the Europeans probably got their first ideas of modern pisciculture. Both in Europe and America the industry has become of such importance as to be more or less completely supported by Government funds. In Europe the hatcheries, over four hundred in number, are largely private enterprises, but such are as yet comparatively rare in the United States and Canada. The United States far surpasses all other countries in the extent of this work under Government patronage. The Federal Government supports twenty-eight hatcheries at various favorable places, and one steamer, the Fishhawk, a sort of floating hatchery, exclusively used in the actual culture of fishes or in the investigation of problems pertaining thereto. The number of fish handled in 1899, either as eggs, fry, fingerlings, yearlings, or adults, aggregated 1,056,371,898. Of this number 986,000,000 were fry and fingerlings, and 5,000,000 yearlings and adults. Besides these many of the States support hatcheries for the particular fishes of importance in their territories. (See below.) The purpose of the governmental hatcheries is either to stock new waters with desirable species or to maintain by planting the supply in waters already tenanted.
In most species it is impracticable to carry culture much beyond the stage of hatching, or ‘fry,’ as the hatchings are called. This is true of all the strictly marine forms such as the cod and flat fishes. In many of the fresh-water species, such as the various salmons and sunfishes, they are often nourished and protected in suitable ponds until they have become three or four inches long—‘fingerlings,’ as they are then called—before planting. They may even be carried for another year and planted as yearlings.
It is now established that waters thus stocked or replenished have not only been able to maintain their supply of fishes, but have greatly increased it. Pacific waters have been successfully stocked with Atlantic species, and almost exhausted streams in various parts of the United States have been successfully restored. In some species the eggs are not handled, but the spawning fishes are provided with favorable ponds for spawning purposes, where their eggs are protected from enemies, given suitable temperature, etc. This is the case with members of the Centrarchidæ, such as the black bass, which build a nest and guard the eggs during incubation. The young when hatched are either taken from the ponds and fed in suitable troughs until better able to shift for themselves, or are supplied with food in the ponds themselves. In most species, however, the eggs are artificially expelled from the body into suitable receptacles, in which they are fertilized by the addition of milt similarly obtained from the males. After a few moments the eggs are transferred to running water, where they are kept and taken care of until the embryos emerge. The exact method employed in fertilization, but especially the subsequent handling of the eggs during incubation, varies considerably with the character of the egg.
Treatment of Eggs. Nearly all fish-eggs are spherical in shape. The true portion, which is heavily charged with yolk, is inclosed by a membrane varying greatly in character. This membrane may be adhesive to any foreign object or to adjoining eggs, or it may be supplied with various modifications of filaments which cause the eggs to become entangled with each other and with foreign objects, such as weeds. These properties necessitate different methods in their handling during incubation. Again, eggs may be pelagic, i.e. buoyant, lighter than the water, or heavy, sinking to the bottom. Some eggs, as those of the whitefish and shad, are only slightly heavier than water, i.e. semi-buoyant.
Pelagic eggs belong to the cod, flatfish, mackerel, tautog, etc. Such eggs are incubated in a way quite different from the heavy eggs; in nature they are extruded in the water and rise to the surface, where they develop. Such eggs usually hatch in a very short time, from a few days to two or three weeks. The apparatus now used for hatching pelagic eggs is the McDonald tidal box. The water enters through the cheesecloth bottom and through a small hole at one end, the latter giving the water and eggs within the box a gentle rotary motion. By means of an automatic siphon the water is also made to rise and fall at short intervals, thus insuring a more perfect renewal of the water.
Heavy eggs, as those of the salmon and trout, are spread out on small wire-bottomed trays. These are placed in tiers in long troughs, into which the water enters at one end and by an arrangement of partitions is made to flow from below upward through the tiers of eggs, thus bathing them, and flowing out at the opposite end of the trough. During development in these trays constant attention is necessary to avoid too strong currents through the troughs, thereby shifting the eggs, and especially to remove the dead eggs, which are attacked by a fungus, and, if allowed to remain, will speedily contaminate the whole lot.
Semi-buoyant eggs, as those of the whitefish, are hatched successfully in the McDonald jar. This has a rounded bottom, and the water is introduced by a glass tube extending through the lid to near the bottom. The water entering slowly keeps the eggs in slow motion, to prevent them from ‘banking’ or gathering in lumps. The water escapes through the top by a tube or a sort of
