Editing Fish farming (section)

== Slaughter methods ==
{{main|Fish welfare at slaughter}}

Tanks saturated with carbon dioxide have been used to make fish unconscious. Their gills are then cut with a knife so that the fish bleed out before they are further processed. This is no longer considered a humane method of slaughter. Methods that induce much less physiological stress are electrical or percussive stunning and this has led to the phasing out of the carbon dioxide slaughter method in Europe.<ref>[[Victoria Braithwaite]] (2010). ''Do fish feel pain?'' Oxford University Press, p. 180</ref>

=== Inhumane methods ===
According to T. Håstein of the National Veterinary Institute (Oslo, Norway), "Different methods for slaughter of fish are in place and it is no doubt that many of them may be considered as appalling from an animal welfare point of view."{{sfn|Håstein|2004|pp=224}} A 2004 report by the [[EFSA]] Scientific Panel on Animal Health and Welfare explained: "Many existing commercial killing methods expose fish to substantial suffering over a prolonged period of time. For some species, existing methods, whilst capable of killing fish humanely, are not doing so because operators don't have the knowledge to evaluate them."{{sfn|European Food Safety Authority|2004|pp=22}} Following are some less humane ways of killing fish.
* Air asphyxiation amounts to suffocation in the open air. The process can take upwards of 15 minutes to induce death, although unconsciousness typically sets in sooner.{{sfn|Benson|pp=23}}
* Ice baths or chilling of farmed fish on ice or submerged in near-freezing water is used to dampen muscle movements by the fish and to delay the onset of post-death decay. However, it does not necessarily reduce sensibility to pain; indeed, the chilling process has been shown to elevate [[cortisol]]. In addition, reduced body temperature extends the time before fish lose consciousness.{{sfn|Yue|pp=4}}
* [[Hypercapnia|CO{{sub|2}} narcosis]]
* Exsanguination without stunning is a process in which fish are taken up from water, held still, and cut so as to cause bleeding. According to references in Yue,{{sfn|Yue|pp=6}} this can leave fish writhing for an average of four minutes, and some catfish still responded to noxious stimuli after more than 15 minutes.
* Immersion in salt followed by gutting or other processing such as smoking is applied to eel.<ref name="Fishcount">{{cite web|url=http://fishcount.org.uk/farmed-fish-welfare/farmed-fish-slaughter|title=Slaughter of farmed fish – fishcount.org.uk|access-date=30 January 2016}}</ref>

=== More humane methods ===
Proper stunning renders the fish unconscious immediately and for a sufficient period of time such that the fish is killed in the slaughter process (e.g. through exsanguination) without regaining consciousness.
* Percussive stunning involves rendering the fish unconscious with a blow on the head.
* Electric stunning can be humane when a proper current is made to flow through the fish brain for a sufficient period of time. Electric stunning can be applied after the fish has been taken out of the water (dry stunning) or while the fish is still in the water. The latter generally requires a much higher current and may lead to operator safety issues. An advantage could be that in-water stunning allows fish to be rendered unconscious without stressful handling or displacement.{{sfn|Yue|pp=7}} However, improper stunning may not induce insensibility long enough to prevent the fish from enduring exsanguination while conscious.{{sfn|European Food Safety Authority|2004|pp=22}} Whether the optimal stunning parameters that researchers have determined in studies are used by the industry in practice is unknown.{{sfn|Yue|pp=7}}