In a message of 19 April Stephen Grabacki asked about bleeding of 'dead' and
'live' salmon. Literature in fish technology recommend bleeding of fish soon
after capture or harvesting in order to improve the colour and appearance of
fillets cut from the fish. For example see the passage in Connell's book
'Control of Fish Quality', (pp 60/61 in the current, 4th edition). There he
writes that blood in vessels and organs remain fluid for up to about 30
minutes after capture and recommends that fish should be bled within this
time. Botta and colleagues looked at the effect of delays before bleeding on
the quality of cod fillets, (Effect of bleeding/gutting procedures on the
sensory quality of fresh raw Atlantic cod (Gadus morhua), Canadian Institute
of Food Science and Technology Journal, 1986, 19, 186_190), but I do not
have a copy of the paper to check the findings.
The main burden of Stephen's message though is the comparison between
bleeding 'live' and 'dead'. There is a difficulty here in knowing when the
fish are dead. In typical trawling practice most of the fish from the trawl
are dead when discharged to the deck in the sense they are not moving and
are flaccid. Death has occurred by anoxia because crowding in the cod end
prevents movement of the opercula. It is likely that the hearts in these
fish are still beating, but it does not matter since good gutting practice
will remove the heart and the blood still drains away during subsequent
storage in ice. The common practice of slaughtering of farmed salmon is to
stun the fish by a blow to the head with a club, percussive stunning, or by
CO2 anaesthesia, followed by cutting of the gills. Death is due to the
exsanguination. There is a good summary of slaughtering practices for farmed
fish and the related causes of death in the chapter by Robb, 'The
relationship between killing methods and quality' in: Farmed Fish Quality
(edited by S.C. Kestin & P.D. Warriss). Oxford, UK: Fishing news Books, pp
220-233.
It seems clear to me that the answer to Stephen's questions are: yes, there
is definitely a benefit to the appearance of the fillets of salmon,
especially smoked fillets, in allowing the fish to bleed before filleting
and processing; and no, it does not matter - not taking account of humane
considerations - if the fish are technically alive or dead when the bleeding
occurs so long as it is soon after slaughter.
Evert Liewes in his message of 19 April refers to prospective legislation in
the Netherlands requiring that farmed fish be instantaneously killed by
electric shock, and suggests that supermarkets will ask for guarantees that
fish have been instantaneously killed. Is instantaneous killing possible,
and is it required in humane slaughter? My interest in the slaughter of
farmed fish is in its interaction with the quality of the subsequent product
as food, not in the physiology of death, but in my reading of the literature
on slaughtering, (much of this literature emanates from a group at the
Veterinary School of the University of Bristol and in the last few years
there has been collaboration between this group and the DLO-RIVO laboratory
cited by Evert), I note that the physiologists refer to the initial step in
the slaughtering process as stunning, not killing. My understanding of the
slaughtering of land animals is that the initial stage is stunning by the
captive bolt or by electric shock and death follows by exsanguination. This
non-instantaneous killing process of land animals is accepted by
supermarkets, and animal welfare bodies seem to accept the 2-stage
slaughtering process as humane. In Britain the 'Report on the welfare of
farmed fish' from the Farm Animal Welfare Council recommended, in respect of
slaughter that: 'If a fish is to be stunned, the stun must cause immediate
loss of consciousness which lasts until death', and 'A fish must not be
stunned until it can be bled or otherwise killed without delay'. Going back
to the original question, it would seem that bleeding is not only good
practice for the quality of the product, but is also a required step in the
slaughtering process.
Peter Howgate
----- Original Message -----
From: <graystar@alaska.net>
To: "Seafood Internet" <seafood@ucdavis.edu>
Sent: Saturday, April 19, 2003 12:53 AM
Subject: bleeding salmon
> Greetings from Alaska -- I know that bleeding a live Pacific salmon
(Oncorhynchus spp.) can improve the quality of the flesh, but how about
"bleeding" a dead salmon? Is there any benefit to allowing blood to drain?
For example, maybe the fish might appear dead, but the heart might still be
pumping a bit. Or, even after the heart has stopped, maybe the blood
coagulates slowly enough to make slitting the throat or the gill rakers
worthwhile. Is it safe to assume that the blood is well-coagulated by the
time the fish goes into rigor? Thank you, in advance, for your guidance.
Regards, -- Steve
>
> Stephen T. Grabacki, FP-C
> President
> GRAYSTAR Pacific Seafood, Ltd.
> P.O.Box 100506
> Anchorage, Alaska
> 99510-0506 USA
> phone: (907) 272-5600
> fax: (907) 272-5603
> graystar@alaska.net
>
>
This archive was generated by hypermail 2b29 : Fri Apr 25 2003 - 04:19:55 PDT