I’ve been looking at hydro/aqua-ponics lately and ran across Azolla. The only real economic reason for the fish is nitrogen. Azolla would be a possible substitute for the fish—need to figure out conversion ratios and space. Would think growing plants has to be more effective then feeding fish but might take up more space.
Azolla’s significance comes from its partnership with several species of bacteria that can manage a trick no plant finds possible by itself: extracting nitrogen from the air and “fixing” it into chemicals such as ammonia, so that it is available to make proteins. Asian rice farmers have known of Azolla’s fertilising properties for at least 1,500 years, and in many places the fern is encouraged to grow alongside rice in paddies—a sort of aquatic version of alfalfa. Dr Pryer’s primary pitch, therefore, is that understanding the genomes of Azolla and its associated bacteria (which she proposes to sequence at the same time) might assist the improvement of this process, and maybe aid its transfer to other plants.
Would work well for cleaning up water on dairy farms as well—solves the surplus phosphorous issue.
…grow at great speed – doubling its biomass every two to three days. The only known limiting factor on its growth is phosphorus, another essential mineral. An abundance of phosphorus, due for example to eutrophication or chemical runoff, often leads to Azolla blooms.”