Fish Culture, the breeding, rearing, and distributing of fish. Fish culture, also called aquaculture, fish farming, and pisciculture, is important in maintaining the supply of food and game fishes, and in extending the area in which they may be caught. Through fish culture, a number of species have been introduced successfully into new areas. The brown trout of Europe, for example, has been naturalized in North America and the North American rainbow trout in New Zealand.

One form of fish culture is the profession and hobby of raising goldfish and tropical fish. Other forms include raising minnows for bait and raising other fish for planting in private waters. In many parts of the world fish are cultured in large quantities, much as a crop for commercial sale. Few species, however, can be successfully raised in this manner; those that can include catfish, yellowtail, carp, and trout.

One of the most important forms of fish farming is practiced by government agencies that raise such fish as salmon and trout to stock public waters. In the United States, both federal and state governments raise and distribute fish. The federal and provincial governments of Canada also breed various species of fish.

Breeders sometimes use selective breeding techniques to produce hybrids that incorporate the best qualities of two or more species. Breeders can improve such important traits as growth rate, disease resistance, tolerance to crowding, and reproductive performance. In some types of fish, hormone injections are sometimes used to increase growth rate and vaccines to prevent disease.

Hatching and Rearing

The places where workers raise fish are called fish hatcheries. Mature fish may be kept at a hatchery, or they may be caught and transferred to a hatchery in the breeding season. There are two main methods of obtaining eggs—the stripping method and the breeding-pond method.

Stripping

The eggs of salmon, trout, and some other fish species are obtained by stripping the fish. In this process the eggs of a number of females are squeezed into a pan by gentle pressure on the bellies of the fish. The milt (sperm) from a male is then squeezed into the pan and mixed with the eggs. A little clean, cold water is then added to the eggs, and the pan is set aside for a short time to allow the milt to fertilize the eggs. The excess milt is washed from the fertilized eggs, and the eggs are placed in cold water to harden. When hardened, the eggs separate, and they can be handled safely.

Hatching Eggs. The eggs of trout and salmon are hatched in trays with wire-mesh bottoms. The trays are placed in tiers in canals (called raceways) or long tanks. Water is admitted at one end and runs off at the other.

The semibuoyant eggs of whitefish and some other species are hatched in large, round-bottomed glass jars. Water enters each jar through a tube that extends to the bottom. Excess water overflows at the tops of the jars. The flowing water keeps the eggs in constant agitation, and carries infertile and diseased eggs to the surface, where they are removed.

Raising Young Fish. For a few days after they hatch, the young fish, or fry, live on the contents of the food sacs below their bellies. The fry are then fed ground beef liver until they become fingerlings, one inch (2.5 cm) or more long. They are then transferred to rearing ponds, where they are fed a less expensive food mixture, such as ground fish, soybeans, and corn meal. Each species is kept separate in the rearing ponds, and fish of the same size are kept together.

Breeding-pond Method

Black bass, catfish, and some other fish species cannot be successfully stripped. Breeding ponds are provided for pairs of these fish. The male bass scoops out a shallow nest with its tail. For catfish, a large can or jar is set in the bank as a nest. The males of both bass and catfish guard the eggs and the fry. When the fry have absorbed the contents of their food sacs, they are transferred to rearing ponds.

How Fish Are Distributed

Some fish are distributed in lakes and streams while they are still fingerlings. Others are not transferred until they are more fully grown. Many trout are not planted until they are of legal size—large enough for fishermen to keep.

In some states, large numbers of trout fingerlings are distributed among conservation and sportsmen's clubs, which raise them in rearing ponds until they are of legal size. The states provide food for the young fish.

Fish are usually carried to lakes and streams in tank trucks provided with air compressors, by which the water can be constantly aerated. In areas difficult to reach by land, fingerlings may be dumped into lakes from airplanes or helicopters.