Editing Fish farming (section)

=== Intensive aquaculture ===
{{More citations needed section|date=February 2021}}
{| class="wikitable" style="float:right;"
|+ Optimal water parameters for cold- and warm-water fish in intensive aquaculture<ref>[http://fisheries.btc.ctc.edu/Manuals/Coldwater%20Fish%20Culture/Stress%20and%20Physiology.PDF "Stress and Physiology"] {{webarchive|url=https://web.archive.org/web/20110816103911/http://fisheries.btc.ctc.edu/Manuals/Coldwater%20Fish%20Culture/Stress%20and%20Physiology.PDF |date=2011-08-16 }} By Dr. BiIl Krise at Bozeman Technology Center, and Dr. Gary Wedemeyer at Western Fisheries Research Center. January 2002</ref>
! Parameter
! Optimal value
|-
| [[Acidity]] || pH 6–9
|-
| [[Arsenic]] || < 440&nbsp;μg/L
|-
| [[Alkalinity]] || > 20&nbsp;mg/L (as CaCO<sub>3</sub>)
|-
| [[Aluminium]] || < 0.075&nbsp;mg/L
|-
| [[Ammonia]] (non-ionized) || < 0.02&nbsp;mg/L
|-
| [[Cadmium]] || {{plainlist|
*< 0.0005&nbsp;mg/L in [[soft water]]
*< 0.005&nbsp;mg/L in [[hard water]]}}
|-
| [[Calcium]] || > 5&nbsp;mg/L
|-
| [[Carbon dioxide]] || < 5–10&nbsp;mg/L
|-
| [[Chloride]] || > 4.0&nbsp;mg/L
|-
| [[Chlorine]] || < 0.003&nbsp;mg/L
|-
| [[Copper]] || {{plainlist|
*< 0.0006&nbsp;mg/L in soft water
*< 0.03&nbsp;mg/L in hard water}}
|-
| [[Supersaturation|Gas supersaturation]] || {{plainlist|
*< 100% total gas pressure
*< 103% for salmonid eggs/fry
*< 102% for lake trout}}
|-
| [[Hydrogen sulfide]] || < 0.003&nbsp;mg/L
|-
| [[Iron]] || < 0.1&nbsp;mg/L
|-
| [[Lead]] || < 0.02&nbsp;mg/L
|-
| [[Mercury (element)|Mercury]] || < 0.0002&nbsp;mg/L
|-
| [[Nitrate]] || < 1.0&nbsp;mg/L
|-
| [[Nitrite]] || < 0.1&nbsp;mg/L
|-
| [[Oxygen]] || {{plainlist|
*6&nbsp;mg/L for coldwater fish
*4&nbsp;mg/L for warmwater fish}}
|-
| [[Selenium]] || < 0.01&nbsp;mg/L
|-
| [[Total dissolved solids]] || < 200&nbsp;mg/L
|-
| Total [[suspended solid]]s || < 80 [[Nephelometric Turbidity Units|NTU]] over ambient levels
|-
| [[Zinc]] || < 0.005&nbsp;mg/L
|}
{{See also|Intensive farming}}
In these kinds of systems fish production per unit of surface can be increased at will, as long as sufficient [[oxygen]], fresh water and food are provided. Because of the requirement of sufficient fresh water, a massive [[water purification]] system must be integrated in the fish farm. One way to achieve this is to combine [[hydroponic]] [[horticulture]] and [[water treatment]], see below. The exception to this rule are cages which are placed in a river or sea, which supplements the fish crop with sufficient oxygenated water. Some [[environmentalist]]s object to this practice.<!-- Explain why - adverse environmental effects, pollutioni -->
[[Image:Abstreifen.JPG|thumbnail|left|250px|Expressing eggs from a female rainbow trout]]

The cost of inputs per unit of fish weight is higher than in extensive farming, especially because of the high cost of [[Feeds for farmed fish|fish feed]]. It must contain a much higher level of [[protein]] (up to 60%) than [[cattle]] feed and a balanced [[amino acid]] composition, as well. These higher protein-level requirements are a consequence of the higher feed efficiency of aquatic animals (higher [[feed conversion ratio]] [FCR], that is, kg of feed per kg of animal produced). Fish such as salmon have an FCR around 1.1&nbsp;kg of feed per kg of salmon<ref>{{cite journal | last1 = Torrissen | first1 = Ole |display-authors=etal | year = 2011 | title = Atlantic Salmon (Salmo Salar): The 'Super-Chicken' Of The Sea? | journal = Reviews in Fisheries Science | volume = 19 | issue = 3| pages = 257–278 | doi=10.1080/10641262.2011.597890| s2cid = 58944349 }}</ref> whereas chickens are in the 2.5&nbsp;kg of feed per kg of chicken range. Fish do not use energy to keep warm, eliminating some carbohydrates and fats in the diet, required to provide this energy. This may be offset, though, by the lower land costs and the higher production which can be obtained due to the high level of input control.

[[Aeration]] of the water is essential, as fish need a sufficient oxygen level for growth. This is achieved by bubbling, cascade flow, or aqueous oxygen. Catfish in genus ''[[Clarias]]'' can breathe atmospheric air and can tolerate much higher levels of pollutants than trout or salmon, which makes aeration and water purification less necessary and makes ''Clarias'' species especially suited for intensive fish production. In some ''Clarias'' farms, about 10% of the water volume can consist of fish [[biomass]].

The risk of infections by parasites such as fish lice, fungi (''[[Saprolegnia]]'' spp.), intestinal worms (such as [[nematodes]] or [[trematodes]]), bacteria (e.g., ''[[Yersinia]]'' spp., ''[[Pseudomonas]]'' spp.), and protozoa (such as [[dinoflagellates]]) is similar to that in [[animal husbandry]], especially at high population densities. However, animal husbandry is a larger and more technologically mature area of human agriculture and has developed better solutions to pathogen problems. Intensive aquaculture has to provide adequate water quality (oxygen, ammonia, nitrite, etc.) levels to minimize stress on the fish. This requirement makes control of the pathogen problem more difficult. Intensive aquaculture requires tight monitoring and a high level of expertise of the fish farmer.

[[File:Aufzuchtbecken.JPG|thumb|right|Controlling [[roe]]s manually]]

Very-high-intensity recycle aquaculture systems (RAS, also Recirculating Aquaculture Systems), where all the production parameters are controlled, are being used for high-value species. By recycling water, little is used per unit of production. However, the process has high capital and operating costs. The higher cost structures mean that RAS is economical only for high-value products, such as broodstock for egg production, fingerlings for net pen aquaculture operations, sturgeon production, research animals, and some special niche markets such as live fish.<ref>{{cite journal | last1 = Weaver | first1 = D E | year = 2006 | title = Design and operations of fine media fluidized bed biofilters for meeting oligotrophic water requirements | journal = Aquacultural Engineering | volume = 34 | issue = 3| pages = 303–310 | doi=10.1016/j.aquaeng.2005.07.004| bibcode = 2006AqEng..34..303W }}</ref><ref>{{cite journal | last1 = Avnimelech | first1 = Y | last2 = Kochva | first2 = M |display-authors=etal | year = 1994 | title = Development of controlled intensive aquaculture systems with a limited water exchange and adjusted carbon to nitrogen ratio. | journal = Israeli Journal of Aquaculture Bamidgeh | volume = 46 | issue = 3| pages = 119–131 }}</ref>

Raising ornamental coldwater fish ([[goldfish]] or [[koi]]), although theoretically much more profitable due to the higher income per weight of fish produced, has been successfully carried out only in the 21st century. The increased incidences of dangerous viral diseases of koi carp, together with the high value of the fish, has led to initiatives in closed-system koi breeding and growing in a number of countries. Today, a few commercially successful intensive koi-growing facilities are operating in the UK, Germany, and Israel.

Some producers have adapted their intensive systems in an effort to provide consumers with fish that do not carry dormant forms of viruses and diseases.

In 2016, juvenile Nile tilapia were given a food containing dried ''[[Schizochytrium]]'' in place of [[fish oil]]. When compared to a control group raised on regular food, they exhibited higher weight gain and better food-to-growth conversion, plus their flesh was higher in healthy [[omega-3 fatty acid]]s.<ref>{{Cite web|url=http://www.gizmag.com/microalgae-fish-oil/43707|title=Scientists take the fish out of fish food|last=Coxworth|first=Ben|date=June 6, 2016|website=www.gizmag.com|access-date=2016-06-08}}</ref><ref>{{Cite journal|last1=Sarker|first1=Pallab K.|last2=Kapuscinski|first2=Anne R.|last3=Lanois|first3=Alison J.|last4=Livesey|first4=Erin D.|last5=Bernhard|first5=Katie P.|last6=Coley|first6=Mariah L.|date=2016-06-03|title=Towards Sustainable Aquafeeds: Complete Substitution of Fish Oil with Marine Microalga Schizochytrium sp. Improves Growth and Fatty Acid Deposition in Juvenile Nile Tilapia ( Oreochromis niloticus )|journal=PLOS ONE|volume=11|issue=6|pages=e0156684|doi=10.1371/journal.pone.0156684|issn=1932-6203|pmid=27258552|pmc=4892564|bibcode=2016PLoSO..1156684S|doi-access=free}}</ref>