The Discolouration of Halibut
From CANDADIAN FISHERMAN
Under the auspices of the Bi
ological Board of Canada, and
working at the Pacific Biologic
al Station, Prince Rupert, Di
rector D. B. Finn, Dr. F. C. Har
rison of McGill University and
Professor W. Sadler of the Uni
versity of British Columbia,
spent the summer working on
the discolouration of halibut.
This trouble has existed for
some time, and scarcely a cargo
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of nanout landed at Prince Ru
pert is altogether tree from the
discolouration. ine cuscoioura
tion is of a pale yellow or yenow
green coiour, located on tne un
der surface of tne fish; at times
the slime that covers tne fisn is
alone infected, out at otner
times it seems Ditten into the
skin. Naturally, this discolour
ation is not desireabie from the
aeaier’s or consumer’s stand
point; it detracts from tne good
appearance of the fisn, and sug
gests early deterioration, in
iact, this is in many cases a jus
tifiable assumption for the mi
cro-organisms causing the
trouble are decomposition of
flesh or protein, and can grow
through the skin and affect the
meat. Many such fish are soft
and not firm to thee touch, and
are often thrown aside by the
graders.
Direct infection experiments
of transferring a sman amount
of the discoloured slime to a
perfectly white fish, showed that
the trouble could be transferred
and subsequently the organisms
directly concerned were isolat
ed. These pure cultures inocu
lated on the white halibut
showed the peculiar discoloura
tion in less than twenty-four
hours, and isolations from the
artificially inoculated fish show
ed that the same organisms
as were originally inoculated
were present in practically pure
culture.
The next step was to trace or
find out the habitat of the or
ganism causing the trouble, and
this was found in the ice and
fresh water used for keeping the
fish cool or for washing purpos
es. Practically all ice supplied
contained this organism in
greater or less numbers, and all
ice sources with one exception
were examined. Furtnerr the
organisms have been repeatedly
isolated from the holds of the
fishing vessels, biiqre water,
landing net, landing platforms,
—in fact from every place that
comes in contact with the fish.
The organisms, of which a num
ber of varieties have been iso
lated, is PSEUDOMONAS FLU
ORESCENS, a well known fresh
water organism. It can grow
well at very low temperatures—
of 34-38 degrees Fahrenheit, and
a few degrees higher—with rap
idity.
Examination of fresh halibut
by samples obtained before the
fish were taken off the hook
and before they touched any
part of the boat, showed that
this organism (Pseudomonas
liuorescens) was not present, but
these examinations showed that
the slime and under surface of
the halibut contained numer
ous organisms. Se water at
depths of thirty to forty fath
oms also contained bacteria, but
not the organisms responsible
for the green yellow discoloura
tion.
As over two hundred pure cul
tures have been isolated, it is
necessary to work these out in
detail, and this work is now go
ing on, together with other ex
perimental work on the biology
of the microorganisms of water,
ice, sea water and halibut and
the Biological Board will publish
these results.—Canadian Fish
erman.
And Same Tail
Teacher: Come here Henry.
This essay of yours on ‘Our Dog’
is word for word the same as
your brother’s.”
Henry: “Sure. It’s the same dog