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A King-sized Aquarium that Feeds a Family
You do not have to be an expert to raise fish successfully; basically, it is like managing an oversized aquarium. Fish are raised commercially in large artificial ponds or complex structures, but for individual homeowners and homesteaders a simple backyard tank can produce a significant proportion of a family's protein needs. An aboveground wading pool, 12 feet across and 2 feet deep, can yield 50 to 100 pounds of tasty trout, catfish, or other species in a single growing season of five to six months.
Good Water Is the Key to Productivity
The types of fish you can raise as well as the poundage you harvest depend on three factors: oxygen content of the water, water quality, and water temperature.
Oxygen content. Fish must have oxygen to survive. When oxygen dissolved in the water falls too low, the fish suffocate and die. Oxygen enters water by diffusion from the air and by the action of algae and other water plants.
Oxygen content drops on a sunless day, when plants photosynthesize slowly, and in hot weather, because warm water holds less oxygen than cold water. The fish farmer can get around natural deficiencies by using an aerator to supply needed oxygen. In fact, constant aeration can double the fish harvest, since fish are healthier and grow faster when they have plentiful oxygen.
Many models of aerators are sold by aquaculture supply houses. Some bubble air up from the bottom via perforated pipes or hoses; others spray a fountain of water up into the air. The latter type of aerator has the advantage of providing circulation as it splashes down on the surface of the tank. For a small-scale home operation a sump pump with a short hose attached to jet the water back into the tank can serve as an aerator.
Water quality. The pH (degree of acidity or alkalinity) and the presence of such impurities as heavy metals and organic waste play a part in determining water quality. Fish will not thrive in water with a pH much lower than 6 (acid) or much higher than 8 (alkaline). The ideal pH is 6.5 to 7.
Check the pH of your water regularly: add lime to reduce acidity; add gypsum to reduce alkalinity. Before setting up your tank, have the water tested for such heavy metals as iron, lead, and copper. Even in concentrations as low as three parts per million these substances are toxic to fish. If your water supply chlorinated, filter it through charcoal before using it.
Fish give off nitrogenous wastes in large quantities.
These must not be allowed to accumulate. Algae are effective purifiers in ponds and lakes; but if you are raising fish in a tank, particularly if you are raising trout you will need a recirculating filter. An efficient filter can be made at home from a clean 55-gallon drum filled with crushed rock, gravel, sand, seashells, or special plastic ringlets. Naturally occurring bacteria that grow on the filter medium convert the fish wastes to harmless substances. A small electric pump circulates water to the filter; gravity feeds it back to the tank.
Water temperature. Trout do best in water be-tween 54°F and 56°F, but they can survive lower temperatures as long as the water does not freeze. If the temperature rises to 85°F they will die. A steady supply of water from a cold spring is close to ideal. Catfish, in contrast, thrive at 80°F to 90°F and become torpid below 40°F. If your climate permits, raise trout in the colder months and catfish in the warm season. For best results, match your fish to the climate and let nature work for you.
Setting Up a Backyard Fish Tank
Breeding your own fish entails an extra investment in equipment and labor. Most fish farmers, from large-scale trout ranchers to backyard hobbyists, find it easier to obtain their stock from commercial hatcheries. Fish are purchased as 2- to 6-inch fingerlings and harvested after one growing season (it is seldom economical to carry them longer). The bigger the fingerlings, the bigger the fish you will harvest.
Backyard fish tank is easy to manage and produces plenty of fish for family use. The system requires few components. Tank can be built of cement block painted with waterproof epoxy compound. it can also be made from fiberglass or from wood lined with plastic sheeting.
Even a standard child's wading pool will serve.
1. set up your tank in a level area as close to a water outlet as possible. Fill the tank, then check that the filter and aerator are functioning properly.
2. Run the system for two weeks before the fish arrive to condition the water and permit waste-neutralizing bacteria to become established in the filter.
3. Fish will be delivered in water-filled plastic bags. To avoid thermal shock, place bags in tank until temperatures are equalized, then release fish.
4. Keep the water thoroughly aerated; a good oxygen supply is vital to the health of the fish. A small submersible fountain-type aerator is shown operating here.
5. Feed can be broadcast on the water, but a floating feed rack, easy to make at home, will provide better sanitation and will waste less feed.
6. Harvest fish with a dip net or by draining the tank. if the fish are in a pond, a drag net can be used to harvest large numbers of them at one time.
During the growing season water must be added to the tank regularly to replace water lost by evaporation. When the time comes to harvest the fish, drain out most of the water and scoop the fish up in nets. The fish can be frozen, eaten fresh, or preserved in a variety of other ways (see Preserving Meat and Fish).
If you lack experience in fish farming, plan on stocking about 1 pound of fingerlings for each cubic foot of water- more could overload the system. (Fish farmers think in terms of total fish weight, not numbers.) It is possible to stock more than one species together; in fact, studies show that poly-cultures out yield monocultures provided the species are selected so as not to compete with each other for food or living space. For a sustained yield in farm ponds experts recommend a mixture of 100 largemouth bass and 500 bluegill sunfish per surface acre. The bluegills feed on small water organisms, and the bass feed on the bluegills.
Some pond owners, however, stock bass only, since bluegills tend to over-breed.
The leading types of fish raised in the United States are trout and channel catfish. Both are best raised in monocultures, since they do not compete effectively with other species for food and oxygen. Under proper conditions both gain weight rapidly, and both are excellent for eating.
A tropical fish, the tilapia, holds promise for tank culture in temperate areas, but providing warm water (75°F) for the five-month growing season they need to reach a half-pound size can be a problem. Tilapia are tasty, cheap to feed (they can live largely on algae and garden waste), and tolerant of less-than-perfect water quality. Because they are prolific and might pose an ecological threat if they escaped, tilapia are banned in some states. However, since they die when the water temperature falls to 50°F, they are no problem in northern states.
Carp are also an excellent fish for tank culture. They were among the first species to be raised by man (ancient Chinese records describe their culture as long ago as 500 B.C.), and they are mainly vegetarian. Israeli carp and several species of Asian carp do well in poly-cultures. Since carp are banned in many states, check with your conservation officer before stocking them.
Feeding Your Fish
For intensive fish culture supplementary feeding is required. If the fish are to reach harvesting size (1/2 to 1 pound) in one growing season, trout and catfish need high protein rations. Commercial feeds supply protein, vitamins, and minerals in the correct proportions; fish scraps are an acceptable substitute. Experimenters have devised mixtures of chopped earthworms, soy flour, grain meal, and midge larvae. Tilapia and carp have been raised successfully on a diet of algae and grass clippings fortified by small doses of animal manure. Feed your fish at the same time every day, gradually increasing the rations as they grow so that they receive about 3 percent of their body weight daily. (Estimate a gain of about 1 pound for every 2 to 3 pounds of feed.) When feed is left over, use less the next day. Overfeeding can cause sanitation problems.
Sources and resources:
Bardach, John E., John H. Ryther, and William O. McLarney. Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms. New York: John Wiley, 1974.
Bennett, George W. Management of Lakes and Ponds, 2nd ed. Melbourne, Fla.: Krieger, 1983.
Huet, Marcel. Textbook of Fish Culture: Breeding and Cultivation of Fish. Cambridge, Mass.: Blackwell Scientific Publications, 1994.
Spotte, Stephen H. Fish and Invertebrate Culture: Water Management in Closed Systems. New York: John Wiley, 1979.
Yoo, Kyung H., and Boyd, Claude E. Hydrology and Water Supply for Pond Aquaculture. New York: Chapman & Hall, 1993.