Editing Fish farming (section)

=== Integrated recycling systems ===
{{Main|Aquaponics}}
[[File:Unifish fish farm.JPG|thumb|Aerators in a fish farm ([[Ararat plain]], [[Armenia]])]]
One of the largest problems with freshwater pisciculture is that it can use a million gallons of water per acre (about 1 m<sup>3</sup> of water per m<sup>2</sup>) each year. Extended [[water purification]] systems allow for the reuse ([[recycling]]) of local water.

The largest-scale pure fish farms use a system derived (admittedly much refined) from the [[New Alchemy Institute]] in the 1970s. Basically, large plastic fish tanks are placed in a greenhouse. A [[hydroponic]] bed is placed near, above or between them. When tilapia are raised in the tanks, they are able to eat algae, which naturally grow in the tanks when the tanks are properly fertilized.<ref>{{Cite web |title=Tank culture of tilapia |url=https://thefishsite.com/articles/tank-culture-of-tilapia |access-date=2022-07-11 |website=thefishsite.com |date=November 2005 |language=en}}</ref>

The tank water is slowly circulated to the hydroponic beds, where the tilapia waste feeds commercial plant crops. Carefully cultured microorganisms in the hydroponic bed convert [[ammonia]] to [[nitrate]]s, and the plants are fertilized by the nitrates and [[phosphate]]s.Other wastes are strained out by the hydroponic media, which double as an aerated pebble-bed filter.<ref>{{Cite web |title=Aquaculture |url=https://www.environmentalleverage.com/Aquaculture.htm |access-date=2022-07-11 |website=www.environmentalleverage.com}}</ref>

This system, properly tuned, produces more edible protein per unit area than any other. A wide variety of plants can grow well in the hydroponic beds. Most growers concentrate on [[herb]]s (e.g. [[parsley]] and [[basil]]), which command premium prices in small quantities all year long. The most common customers are [[restaurant]] wholesalers.<ref>{{Cite web |last1=Pap |first1=Dawn |last2=rea |date=2019-05-22 |title=What are the Different Types of Restaurant Suppliers? |url=https://upserve.com/restaurant-insider/what-are-the-different-types-of-restaurant-suppliers/ |access-date=2022-07-11 |website=Restaurant Insider |language=en-US}}</ref>

Since the system lives in a [[greenhouse]], it adapts to almost all temperate climates, and may also adapt to [[tropical climate]]s.
The main environmental impact is discharge of water that must be salted to maintain the fishes' [[electrolyte]] balance. Current growers use a variety of proprietary tricks to keep fish healthy, reducing their expenses for salt and wastewater discharge permits. Some veterinary authorities speculate that ultraviolet ozone disinfectant systems (widely used for ornamental fish) may play a prominent part in keeping the tilapia healthy with recirculated water.{{Citation needed|date=February 2021}}

A number of large, well-capitalized ventures in this area have failed. Managing both the biology and markets is complicated. One future development is the combination of integrated recycling systems with urban farming as tried in Sweden by the [[Greenfish recirculation technology|Greenfish Initiative]].<ref>Berggren, Alexandra (2007) [http://www.stockholmresilience.org/download/18.aeea46911a31274279800082877/Berggren+NGG+07+Thesis.pdf Aquaculture in Sweden towards a sustainable future?"] Master's Thesis, Stockholm University</ref><ref>McLarney, William ''Freshwater Aquaculture: A Handbook for Small Scale Fish Culture in North America''</ref>