Bay Soundings | volume five o number one | winter 2006         
  COVERING TAMPA BAY AND ITS WATERSHED      


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Aquaponics combines aquaculture and hydroponics, the cultivation of plants in a nutrient solution rather than soil. More than half of the waste produced by fish is in the form of ammonia, which is converted to nitrates by beneficial bacteria that live in water and soil. Plants readily absorb the nitrates in an aquaponic system, improving water quality for the fish as well as providing a sustainable, organically grown food source.

Home-grown Aquaponics

Home-grown aquaponic systems can provide families with hundreds of pounds of fish and fresh vegetables year-round. The system at the Morningstar facility, shown below, was built with easily available materials including concrete block and plywood, a waterproof tarp, a plastic barrel and PVC piping.

A complete aquaponic system can be built in approximately 150 square feet, although some larger systems cover many acres. The smallest pond is typically about 500 gallons. Under average conditions, three gallons of water are required for each fish, and every 10 gallons of water in the tank supports two square feet of growing area for vegetables.

Most aquaponic systems use tilapia, a warm-water fish native to Israel where it has been farmed for 2500 years, because theyâre extremely fast growing, tolerate poor water quality and use a wide variety of plant-based foods, including duck weed growing on the surface of the water.

A 500-gallon tank can produce about 150 pounds of fish per year, with fish typically harvested every six months at about 1.75 pounds. Tilapia are considered to be highly efficient fish, gaining approximately one pound for every 1.5 pounds of food they are fed. In most home systems, fish should be fed commercial fish food three to four times daily, but automatic feeders are available for families who arenât home during the day.

Systems designed to produce food, like that shown at left, typically consist of three separate chambers: a fish tank, a biofilter and a hydroponic growing area. The system should be designed so that water is pumped from the bottom of the fish tank into a biofilter (the barrel at the front of the photo) where solid waste is captured. Biofilters must be cleaned weekly, and those nutrients can be directly applied to plants growing in soil.

From the biofilter, water is pumped to the top of a slanted hydroponic growing area, most often constructed with PVC piping. The typical system uses an inert growing medium, such as porous clay pellets or rockwool, a spun glass wool made of volcanic rock, to hold roots in place while water moves through the system and overflows back into the fish pond.

The water in most aquaponic systems will have high levels of nitrates with lower levels of phosphate that encourages green leafy growth, so plants like lettuce, bok choy and herbs are particularly well suited. Vegetables and fruits, like cucumbers and tomatoes, can be harvested but may have more leaves and fewer fruits than those grown with more balanced nutrients.

Water should be tested weekly for pH, electrical conductivity and nutrients, but battery-powered test kits make testing simple. In most systems, 25% of the water should be changed on a monthly basis, siphoning it from the bottom of the tank to capture any remaining nutrients and biosolids.

Morningstar Fishermen offers one-day seminars on aquaponics throughout the year. For more information, visit www.morningstarfishermen.org or call 352-523-2722.