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Fish slaughter is the process of killing fish, typically after harvesting at sea or from fish farms.

TODO: Maybe change title to "Fish slaughter welfare" or "Welfare in fish slaughter" or something

Numbers

According to the Food and Agriculture Organization, a total of 156.2 million tons of fish, crustaceans, molluscs, and other aquatic animals were captured in 2011. This is a sum of 93.5 million tons of wild animals and 62.7 million tons of farmed animals. 56.8% of this total was freshwater fish, 6.4% diadromous fish, and 3.2% marine fish, with the remainder being molluscs, crustaceans, and miscellaneous.Cite error: A <ref> tag is missing the closing </ref> (see the help page).

say how many are slaughtered by what methods; make it clear that electric stunning isn't the norm worldwide

Welfare indicators

Research on fish suffering during slaughter relies on measures to indicate when fish are conscious and experiencing pain. Some indicators used by welfare studies include

• Behavior
  • Swimming, gill movement, eye movement in response to body reorientation, reaction when turned upside down, etc.
• Electrical measures
  • EEG, ECG, evoked responses, etc.
  • These are quite accurate but also require high levels of expertise.
• Haematic measures
  • Cortisol, plasma glucose, plasma lactate, haematocrit, etc.
• Tissue measures
  • Indicators of stress in the muscle tissue, like lactic acid, pH, and the catabolites of ATP.
  • These indicators typically also correlate with lower-quality meat.

Following electric stunning, as fish gradually resume consciousness, they begin to make rhythmic gill-cover movements. Based on EEG correlations, it's believed that if stunned fish have not yet resumed rhythmic gill patterns, they remain insensible. This can be used as a convenient assessment tool for the effectiveness of electric stunning.

Inhumane methods

Air asphyxiation

This is the oldest slaughter method and is very inhumane because fish die over a course of up to an hour. Meat quality and shelf life are also diminished.

Ice bath

Also called live chilling, this method involves putting fish in baths of ice water, where they chill and eventually die of anoxia. Because chilling slows metabolic rate and oxygen needs, it actually prolongs the duration until death, with some species taking more than an hour to die. On these grounds, the Farm Animal Welfare Council's 1996 report stated: "The cooling of live trout on ice after they have been removed from water should be prohibited." On the other hand, later research suggested that for warm Mediterranean species like sea bream and sea bass, the method might at least be preferable to regular asphyxiation, with fish showing lower stress indicators.

CO₂ narcosis

Most often applied for salmon and trout, CO₂ narcosis involves filling the fish water with CO₂ in order to produce acidic pH, which injures the brain. The procedure is apparently painful, as evidenced by fish swimming vigorously and trying to get out of the tank. CO₂ immobilizes the fish within 2-4 minutes, but the fish remain conscious until subsequent stunning.

Potentially more humane methods

Percussive stunning

Also known as knocking, percussive stunning involves hitting the fish's brain with a wooden or plastic club, called a priest. One or two blows done well can disrupt the brain sufficiently to render the fish insensible and potentially even kill it directly. However, applying this method properly requires training and effort. For some fish species, there are automated tools, like a pneumatic club for salmon. However, building an automated machine to process, orient, percussively stun, and bleed bulk quantities of small fish would be difficult.

The method must be applied one fish at a time and so is typically only used for large fish, like salmon and trout. If the operator is skilled, percussive stunning can be among the most humane methods and can also yield high meat quality. One comparison of slaughter methods found that percussive stunning had the best welfare performance as measured by low haematocrit, low plasma glucose, low lactate, and high muscle energy charge.

Spiking

Also known as ikejime, this method involves sticking a sharp spike through the brain of the fish. If done properly, it can kill quickly, though if the operator misses the brain, the results may be traumatic. Like percussive stunning, it happens one fish at a time and so is mainly done for large species like tuna and salmon.

Electrical stunning

Electricity can be relatively humane if applied correctly. Electricity may introduce bleedspots, so proper settings are required. If electrical parameters are not optimized, electrical stunning may produce immobility without loss of consciousness.

Ace Aquatec system

Jeff Lines and his collaborators attempted to improve electric stunning of fish. They observed that past stunning attempts had been either too aggressive (resulting in haemorrhages and broken bones that reduced meat quality) or else too lax (meaning that the fish likely were not rendered unconscious). Lines et al. determined that stunning for 60 seconds in an electric field of 250 V/m r.m.s. with a sinusoidal waveform of 1000 Hz was capable of rendering trout permanently unconscious without degrading meat quality.

In follow-up to the research of Lines, John Ace-Hopkins of Ace Aquatec Limited in the UK developed a commercial-quality stunning system called HS1 in 2003. The system includes an 18-meter tube into which the fish are fed. They're first stunned, and then they're passed along to maintenance tubes that keep them unconscious. The machine determines the appropriate voltage based on water conductivity. HS1 is designed to handle 6 tons of fish per hour. The machine was widely adopted in the UK, and now an estimated 80% of UK trout are stunned using it.

The UK Humane Slaughter Association (HSA) recognized this work by designating Lines and Ace-Hopkins as the joint recipients of its 2011 Humane Slaughter Award, which was presented at HSA's Centenary International Symposium by professor Temple Grandin. According to HSA's James Kirkwood: "Before ten years ago there was no way to humanely kill farmed fish en masse – they died slowly through suffocation when harvested from the water. This welfare benefit affects millions of fish."

TODO: - add HS2 and HS3 (http://www.aceaquatec.com/HS2.htm) - Keep reading Lines2003 starting from p. 145 - wild salmon direct thing

Current research

Regulations

• UK law?
• EFSA

Notes

1. ^ Poli, B.M. (2005). "Fish welfare and quality as affected by pre-slaughter and slaughter management". Aquaculture International. 13: 29–49. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
2. Kestin, S.C. (1995). "The effect of CO2, concussion or electrical stunning of rainbow trout (Oncorhynchus mykiss) on fish welfare". Proc. Int. Conf. Aquaculture Europe on Quality in Aquaculture, Gent, Belgium. European Aquaculture Society Special Publ. 23: 380–381. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
3. ^ Cite error: The named reference Lines2003 was invoked but never defined (see the help page).
4. Farm Animal Welfare Council. "Report on the welfare of farmed fish - Recommendations: trout". Retrieved 13 February 2014.
5. Poli, B.M. (2002). "Biochemical stress indicators changes in sea bass as influenced by the slaughter method". Proceeding of the ‘‘Aquaculture Europe 2002: Sea Farming Today and Tomorrow’’. 32: 429–430. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
6. Van der Vis, H. (2003). "Is humane slaughter of fish possible for industry?". Aquaculture Research. 34: 211–220. Retrieved 13 February 2014. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
7. "Pipeline Stunner". Ace Aquatec. Retrieved 29 March 2014.
8. "Awards Given For Dedication To Fish Welfare". The Fish Site. 5M Publishing. 13 July 2011. Retrieved 29 March 2014.

Further reading

External links