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In the discussion of this topic it is necessary to differentiate 'pithing'
and 'spiking'. Spiking, described in Ken's message, is the process of
destroying the brain by passing a spike through the skull into the brain.
Pithing goes further than this and is the process of inserting a wire into
the spinal column of the fish to destroy the spinal cord either through the
skull after spiking or from a deep cut through the vertebral column behind
the head, described in the original message from Richard Lord. Spiking
renders the fish unconscious so that it does not struggle and a similar
effect is caused by giving the fish a hard blow to the head, a method of
stunning farmed salmon on harvesting. Though the fish is rendered
irreversibly unconscious by spiking of by stunning, all muscle activity does
not cease. The muscle at least twitches, if not occasionally flaps. Pithing
stops all muscle activity. The various methods of killing fish, or letting
fish die, affects the time taken for the fish to enter rigor mortis, and to
some extent the time in rigor. I shall not try to summarise the biochemistry
of the rigor process and the way the killing methods affects the
biochemistry, but pithing does maintain glycogen levels in the muscle as
Richard recalls. It should be noted that when different methods of
slaughtering fish are compared, all of the glycogen is ultimately converted
to lactic and the post rigor pHs of the flesh are the same; what is
different between the killing methods is the time course of the glycogen
depletion and lactic acid formation.
Delaying the onset of rigor is important for some uses, for example, for
sushi products, and there is an advantage in pithing fish. For other
outlets, for example, production of fillets, there is no advantage, and some
disadvantages, in delaying onset of rigor. Where the effects of killing
methods on subsequent spoilage have been studied, there has been no effect
of killing method on storage life.
I had not come across the effect of spiking in reducing the time to cool
down described by Ken Hildebrand. I wonder if it the result of inhibiting
twitching of muscle and the consequent heat generation, or is there some
other effect on the biochemistry of the fish.
I am intrigued by Peralta's message. How do you pith a cuttlefish, and what
aspect of quality is preserved?
Peter Howgate
Some references:
Amano, K., Bito, M. & Kawabata, T., 1953, Handling effects upon biochemical
change in the fish muscle immediately after catch I. Difference in
glycolysis in the frigate mackerel killed by various methods. Bulletin of
the Japanese Society of Scientific Fisheries, 19, 487-498.
Ando, M., Banno, A., Haitani, M., Hirai, H., Nakagawa, T. & Makinodan, Y.,
1996, Influence on post-mortem rigor in fish body and muscular ATP
consumption by the destruction of spinal cord in several fishes. Fisheries
Science, 62, 796-799.
Azam, K., Mackie, I.M. & Smith, J., 1989, The effect of slaughter method on
the quality of rainbow trout (Salmo gairdneri) during storage in ice.
International Journal of Food Science and Technology, 24, 69-79.
Boyd, N.S., Wilson, N.D., Jerrett, A.R. & Hall, B.I , 1984, Effects of brain
destruction on post harvest muscle metabolism in the fish kahawai (Arripis
trutta). Journal of Food Science, 49, 177-179.
Iwamoto, M., Yamanaka, H., Abe, H., Ushio, H., Watabe, S. & Hashimoto, K.,
1988, ATP and creatine phosphate breakdown in spiked plaice muscle during
storage, and activities of some enzymes involved. Journal of Food Science,
53, 1662-1665
Jerrett, A.R. & Holland, A.J., 1998, Rigor tension development in excised
"rested", "partially exercised" and "exhausted" chinook salmon white muscle.
Journal of Food Science, 63, 48-52.
Mochizuki, S. & Sato, A., 1996, Effects of various killing procedures on
post-mortem changes in the muscle of chub mackerel and round scad. Nippon
Suisan Gakkaishi, 62, 453-457.
Nakayama, T., Matsuhisa, M., Yamaura, M., Sumiyoshiyama, T. & Ooi, A., 1997,
Delayed example in rigor mortis of spinal cord destroyed plaice detected by
measurements of isotonic contraction and isometric tension. Fisheries
Science, 63, 830-834.
Nakayama, T., Toyoda, T. & Ooi, A., 1996, Delay in rigor mortis of red
sea-bream by spinal cord destruction. Fisheries Science, 62, 478-482.
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