THE INTEGRAL URBAN HOUSE

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If you are determined to raise fish in your urban back yard, some degree of intensiveness will be required to increase per area productivity to the point where it can make a significant contribution to the family's diet. The rewards are likely to be educational, symbolic, and gustatory rather than economic. However, if water from the pond is used in the garden, the fertilizer equivalent of the nutrients supplied should be considered as an additional benefit. Since it will probably cost at least $100 to construct a 100-square-foot pond and several hundred dollars more to build a pump and filter system, the initial costs are high . . . and if you can produce more than 25 pounds of fish a year from such a pond, you will be in the forefront of America's backyard aquaculture innovators.

By the use of technological means of aeration, waste removal, and temperature control it is possible to reach truly phenomenal productivities, exceeding a pound of fish per cubic foot of water per year . . . but these techniques are extremely energy-intensive, and the cost of electricity keeps going up.

It is probably the course of wisdom for the backyard aquaculturalist to use artificial supports only to promote growth, not to sustain life. This means settling for a moderate degree of intensity and a moderate level of production. Wind- or solar-powered support systems are adequate for this level of intensity. Fish under conditions too severe to allow growth may survive for extended periods of time if they are not too crowded. In such intermittent situations a pond will fluctuate between maintenance and growth.

The aquaculture system in the southwest corner of the Integral Urban House garden employs a unique device, called the Savonius Rotor, to prevent our pond from becoming stagnant and eutrophic. The rotor takes its name from J. Savonius, a Finnish engineer who studied the aerodynamic properties of S-shaped vertical (upright) axis turbines. [EDITOR'S NOTE: See MOTHER NO. 26, page 78 and No. 27, page 39.]

The Savonius can catch winds from any direction, and a gust of seven to eight miles per hour will start the machine moving. With linkage improvised from scrap metal and spare parts, we converted the rotational force to vertical strokes which activate a homemade diaphragm pump submerged in the pond.

The pump raises water to a biological filtration unit which is housed in a steel drum, the top of which is five feet above the surface of the water. Primary filtration of large particles is achieved by a felt bag located on top of the drum, and secondary filtration consists of a bed of crushed oyster shells that fills the drum. The toxic ammonia and growth-inhibiting hormones excreted by the fish are removed by bacteria lodged in the oyster shell bed of the filter. Filtered water passes through a faucet aerator to restore oxygen to the pond to complete the cycle.

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