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Fish slaughter

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

Numbers

fishcount.org.uk


Mid-sized trout farms in the UK may process more than 10,000 fish per hour. They tend to be operated by just a few people, and it may be necessary to kill trout on short notice or even at night.


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
  • 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.

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.

Current research

Regulations

  • UK law?
  • EFSA

Notes

  1. ^ Lines, J.A. (2003). "Electric stunning: a humane slaughter method for trout". Aquacultural Engineering. 28 (3–4): 141–154. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ 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)
  3. Farm Animal Welfare Council. "Report on the welfare of farmed fish - Recommendations: trout". Retrieved 13 February 2014.
  4. 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)
  5. 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)

Further reading

External links