To better document the potential impacts of aquaponics , performance metrics need to be clearly defined and relevant to both economic, environmental, and management objectives. For fish, one of the most important performance parameters is the feed conversion ratio (= amount of feed supplied/increase in weight of fish). While much less common, it is also possible to define a FCR for plants (= amount of feed supplied/increase in weight of plants). This parameter measures how well the wastes from the fish are converted into plant tissue.
In contrast to the , a theoretical value of for nitrogen and phosphorus can be estimated from (a) the composition of feed and plants, and (b) the nutrient retention values:
While it is possible to estimate for both nitrogen (Equation 1) and phosphorus (Equation 2 ), there is only one value for the system. The element with the largest w ill be the controlling element for the aquaponic system. The largest will result in the smallest .
Only 50% of the experimental values fell within this theoretical range. This analysis indicates substandard performance of the plant components of many aquaponics systems. This reduced performance may be due to (a) low nutrient and micronutrient concentrations, (b) suboptimal pH and temperatures, and (c) build up of salts. It is strongly recommended that the value be reported in all future research.