Aquaponics

 

The System

Aquaponics is a culture system that is specifically designed to combine aquaculture, the growing of fish, and horticulture, the growing of plants.  These systems exploit a (bacteria facilitated) symbiotic relationship that exists between fish and plants and is seen by some as a nearly ideal method of producing human food. Aquaponic systems can be scaled to virtually any size, micro to very large.

The Interest

The interest in small, backyard aquaponic systems is driven by many factors:

  • the lure of the obvious freshness of the food one has just picked or harvested;
  • the perception that home produced food is more economical and possible more nutritious than supermarket food;
  • the reduced carbon footprint left by homegrown food as compared to food that has been shipped across the country or around the world;
  • the personal gratification of producing at least part of your food yourself, and
  • food safety – when you produce something yourself, you know what’s on it, what’s in it, how it has been handled or treated, and by whom it has been handled or treated.

Although the United States has one of the safest food supplies in the world, news stories abound on the subjects of bacterial and chemical contamination and adulteration of the public food supply; food product recalls are commonplace.  These reasons and more are convincing many people to at least give aquaponics a try. Interest in commercial aquaponics is also growing.  Supermarkets, farmers’ markets, CSAs (Community Supported Agriculture), and up-scale restaurants are potential outlets for the commercial producer’s products.  The same factors that drive the backyard system also allow the commercial producer to demand premium prices for aquaponic products.

The Principles

The principles that drive an aquaponics system and make it work are basic. Diets fed to fish, if not converted directly to fish flesh exit the fish as waste. If allowed to accumulate, this waste would eventually increase to levels harmful to the fish. In aquaponics, these waste products – solid, liquid, and gaseous – are viewed as assets rather than as liabilities.  They are broken-down within the system by bacterial action and provide most, though sometimes not all, of the nutrients that plants require to grow and thrive.  Some, if not all of these nutrients, are taken-up through the plant roots and become concentrated in plant tissue, allowing for their easy removal from the system by simply harvesting the plants. In a properly designed, stocked, and managed system, this ‘nutrient harvesting’ cleans the water sufficiently to provide a healthy environment for the fish.  Since the fish and the plants are dependent on one another for their health and wellbeing, each must flourish if the other is to flourish.

The Management

Most aquaponic systems are managed in a way that allows for both a relatively constant nutrient input (amount of fish feed fed) and nutrient removal capacity (fish and plant harvesting).  Therefore, it is prudent that the design of the system allows for a balance between the amount of food fed to the fish and the amount of nutrients the fish and plants will be able to concentrate and remove at all times. Alternatively, variants of this simple system could incorporate an additional bio-filter and/or a mechanical waste removal system.  These systems, however, require additional infrastructure and waste treatment. An aquaponics system which maximizes the use of nutrient input (fish feed) within the system both reduces or eliminates the solid waste the culturist must put to other uses or dispose of and reduces the amount of make-up water needed by not flushing the system.  Although this amount of water is low, the system is no longer a ‘stand-alone’ system because it creates a byproduct that must be dealt with in some manner.  Possible uses for this waste include the making of compost, compost tea or fertilizer.  If ‘zero water exchange’ is the goal, this is another factor as the solid waste is removed from the system as an aqueous slurry. Unfortunately, most systems designed to utilize all of the fish waste internally produce relatively small quantities of fish compared to those systems designed to remove large quantities of solids.  It takes relatively little waste from fish fed a high quality, complete feed to supply the majority of nutrients a large area of plants can utilize. Most aquaponic systems can be described as ‘closed, recirculating systems’, meaning that the water is used, filtered, and used again and again with minimal flushing to remove excess solids.  Only water lost through evaporation from uncovered water surfaces, evapotranspiration from plant leaves, the removal of plants and fish containing water, the splashing of water by the fish, and minimal filter flushing need be made-up.

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