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Uses of Rearing Ponds

Rearing ponds are pools where newly hatched fish (fry) are introduced and allowed to grow in a protected environment. Ponds are free of larger fish that would usually predate fry. They are commonly covered with netting, giving protection from animals and birds. Ponds are fertilized to increase food plants and plankton. Fry also receive supplemental feed, which produces superior growth and rapid maturation. Rearing pools may be man-made structures at hatcheries or natural pools utilized in the wild.

Pond Rearing Method
- Brood fish are milked of eggs and sperm; fertilized eggs are incubated in small tanks until larvae hatch. This step increases hatchling survival rates from 10 percent under natural predated conditions to almost 100 percent. Fry are transferred to warm, shallow rearing ponds for up to one year. After this time, they are termed "fingerlings." Fingerlings are transferred to further ponds until attaining marketable or game-fishing size. Quarantining ensures freedom from disease or parasites at every stage.
Artificial Rearing Ponds
- Man-made rearing ponds may be either natural-looking ponds dug into the ground or plastic or fiberglass holding tanks. Tanks provide greater control over ambient conditions and monitoring of feeding and growth. Some species require different conditions at each growth stage. Fry in tanks can readily be "graded" into different sizes. Separating different sizes into different rearing ponds prevents them from eating one another. Rearing ponds in the ground remain the world's most common commercial fish-rearing method.
Using Natural Ponds
- Well-stocked natural pools are unsuitable as rearing ponds -- the inhabitants will eat the fry. Ponds can be used "opportunistically" when fish populations are depleted after a hard winter. Alternatively, inhabitant fish may be deliberately killed before introducing fry. This measure is controversial. Traditionally it involves poisoning fish with rotenone, a plant extract. Fertilizing natural ponds to induce algal bloom and plankton growth is likewise controversial, since it alters the natural balance, impacting other wildlife.
Food Production
- Rearing ponds are used to raise food fish including salmon, snapper, tilapia, sturgeon, catfish and cod. They are also used in mollusk and crustacean production -- for example, clams, abalone or oysters. In Third World countries, aquaculture can provide high-protein food and vital income to impoverished communities. Villagers near the Tungabhedra Reservoir in India have been raising carp fry in rearing ponds since about 1980. Carp fry have precarious survival rates in the wild. Protecting fry in rearing ponds, then releasing them into the reservoir has boosted the catch available to local fishermen.
Sports Fishing
- Commonly in the United States rearing ponds are used for raising game fish. Walleye, rainbow trout, bass, salmon or other sport fish fry are introduced into rearing ponds in spring. Fingerlings are released into lakes and streams each fall. Ideally, rainbow trout should be 10 to 12 inches long before release. Steelhead are released at 6 to 9 inches; salmon at about 5 inches. Walleye survive better if released while still under 2 inches.
Conservation
- Rearing ponds can also help replenish endangered fish. Pond-raised fingerlings can be reintroduced into the wild after the environment has been cleaned up and over-fishing halted. Farmed salmon both replaces wild salmon on restaurant menus and provides new stock for rivers.
  
  There is some concern, however, that pond-reared fish may have lost characteristics needed for survival in the wild. In conservation work, quarantining for disease and parasites is especially essential.

Animals & Science