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It would be remiss in this chapter not to mention earthworms and their introduction into aquaponics, and thus this chapter concludes with a brief résumé of these detritivore invertebrates and their abilities to convert organic waste into fertilizer. It is said that worms and the way that they digest matter were of interest to Aristotle and Charles Darwin as well as the philosophers Pascal and Thoreau (Adhikary 2012) and they were protected by law under Cleopatra. Earthworms are valued in agriculture and horticulture as they are 'vital to soil health because they transport nutrients and minerals from below to the surface via their waste, and their tunnels aerate the ground' (National Geographic).
Modern vermiculture is attributed to Mary Appelhof, who in the early 1970s and 1980s produced a number of publications on composting with worms. Contemporary vermicomposting occurs on large and small scales with the objective of getting rid of organic waste and producing fertilizer in the forms of compost and 'worm tea'. Worm tea can be produced by soaking worm casts or by leaching the nutrients from the compost through wetting or natural wetting leachate from precipitation.
Vermiponics uses the worm casts of mainly red wriggler worms also known as tiger worms (Eisenia fetida) or (E. foetida) to provide nutrients in a hydroponic system. When worms are introduced into an aquaponic system, we suggest that the system is termed 'vermi-aquaponics' to differentiate the systems. It is thus the introduction of worms into the growing beds of the plant parts of an aquaponic system. It should be noted that vermi-aquaponics is in its infancy and mainly practiced by hobbyists and in research laboratories. The worms are introduced mainly into the plant growing media, usually gravel beds, where they can help to break down any solid waste from the fish and any detritus from the plants and additionally provide additional nutrients for the plants, and they can also be fed to carnivore fish. In most instances the beds are of a flood and drain type, so that the worms are not constantly under water.
Acknowledgements The authors thank National Council for Scientific and Technological Development-CNPq (Project Number 455349/2012-6) and Scientific and Technological Research Foundation of Santa Catarina State-FAPESC (Project Number 2013TR3406 and 2015TR453).