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FISHERIES AND MARINE SERVICE
Translation Series No. 4228
Jellied meat of fish
by S. Konagaya
Original title: ( not given)
From: • Sakana 15: 32-39, 1975
(Tokaiku Suisan Kenkyusho Gyoseki C Shu)
Department of Fisheries and the Environment
Fisheries and Marine Service
Vancouver Laboratory
Vancouver, B.C.
1978
17 pages typescript
ZZ
1
JELLIED MEAT OF FISH
Accidents of large fishes.
At the Tsukiji Fish Wholesale in Tokyo, the word "accident"
on a large sheet of paper will catch your eyes. The "accident"
does not mean traffic accident here. It refers.to an obstacle
in dealing with large fishes. When the abnormality of the large
fishes is found after being sold to.a large fish dealer (who cuts
the fishes into smaller portion's in order to sell to many
smaller dealers), it is called "accident". The fishes which
had the accident will be sold at a cheaper price depending on
the severity of the accident.
in the past the majority of the accidents were caused by
jellied meat which is called "azuki" (or red-bean) in yellowfin
tuna and broadbill swordfish or "sashi" in bigeye tuna. In
some cases a whole ship load of yellowfin was spoiled by
"azukil' where the_fish was ice-storaged after being caught in
the Banda Sea or the central south area of the Pacific. In
those severe cases the muscle was so fluidified that the contents
streamed out as soon as a cut was made to the fish by a knife.
A severe case like this.is..;rarelÿ reported these days
probably because freezing storage is replacing ice-storage in
tuna and swordfish fishing.- Jellied meat still:occurs often
in inshore fishing where. they ice-store the catch such as
yellowfin tuna or broadbill swodfish.
But thbir catches are
getting less and less every year, thus the "accident" scene is
becoming rare as whole.
2
There are several other forms of accident. "Shimi"(or stain)
which is caused by the blood.in the muscle is seen often in
the frozen,-broadbill swodfish and the incidence is increasing
due to the increaséd use of freezing storage. "Hoshi"(or star)
which resembles a pearl occurs in the muscle of;broadbill
swordfish which was kept either iced or frozen. The size of
"hoshi" is sometimes as big as a ping-pong ball or even a tennis
ball witl#hite-, brown or green color. "Hoshi" may be a changed
form of the muscle and the incidence occurs in other species of
fish.
Sometimes a fishing spear of a piece of wood is found in
the muscle. "yake"(or scorch) has an appearance of:;cooked
meat, and is seen often in yellowfin tuna and broadbill swordfish which are caught near Japan.
The abnormalities mentioned above are not limited to the
large fishes, though the problems are not reported on the small
fishes such as horse-mackerel and mackerel. The jellied meat
of the large fishes are taken here as an exampl,é because the
appearance is very drastic and the extent of financial damage
is large.
A general picture of the jellied meat problems was given
above.
However the/froblem is actually very complex because
thére are many forms of jellied meat. The fish dealers have
given them various names according to the peculiarities of the
problèms.
Those names vary from place to place and person to
person, giving inconvenience to those who are concerned.
The problem has been an interesting topic for,many researchers
in the past and many papers have been Published, but the problems
were described only as "jellied meat" without refering to which
3
one of the jellied meat problems.
This paper attempts to
clarify the jellied meat problems.
Types of jellied meat.
The jellied meat is described as "azuki" ("mitcha" in Osaka
and Kobe areas),
"sashi" ("umi" in Osaka, "butsu" in Kobe),
"mizusashi" or "nagare" ("gari" in Shimizu area),
"konnyaku"
('kobu" in Osaka, "aza" in Kobe), and "fukurobirame"
by the-
Japanese people and milky, messy,, - wormy or chalky in foreign
aiteratures.
The following definition may be appropriate for the jellied
meat: a jellied meat ds a softened tissue of the muscle of a fish,
which has nothing to do with theliormal deterioration of the
muscle after death;
fluidified.
•
or the tissue which became degraded and
The phenomenon is called jellification of the muscle.
Thus the jellied ,- Imeat may be classified into two types,
I) degradation and fluidification of the muscle tissue and II)
softened muscle tissue wïthout degradation and fluidification.
Type I can be called as a typical jellied' meat.
Jellifi-
cation may proceed after death of a fish. Type I can be
further divided into three categories - according to the appearance
of the symptoms, azuki-type, sashi-type and fukuro-type.
Myxosporidia are found in the azuki-type but not in the sashi-
type and the fukuro-type, but this needs further study and is
not used here as a criterion of the classification.
All the other jellied meat which, do not qualify for type
I iqblassified as type II.
Consequently the type II includes -
various forms of jellied meat problems.
4
A characteristic of type II is that the softining of the muscle
starts while the fish:is still alive.
The above is a very rough classification. The characteristics of each of the categories are briefly described below
with some actual examples.
I. The type where muscle tissue is degraded and fluidified.
1) Azuki-type
"Azuki" in yellowfin tuna and broadbill swordfish is .
described here.
In its early stage of development, the cross
section of the muscle reveals some scattered spots which are
as big as a rice grain.
The length of the spot is twice as long
its width. Compared to the normal muscle, the côlor of the spot
is rather whitish.
The center of the spot is transparent which
gives an impression that the center is fluidified (Photo 1).
The tissue which haâ, - those spots becomes gradually jellified
and susceptible to pressure from:outside. You can push, your
finger into the muscle without effort.
In more advanced stage of jellification, the muscle may
become jelly and eventually fluidified, which is refered to
.
as "azuki nagare" (or flux of red-bean).
cation is quite rapid.
The rate of jellifi-
It takes only one to two days for a fish
to become jelly in ice-storage.
The brown colored part of the
muscle does not become jelly.
The symptoms which are described as milky, wormy, messy
or patty in foreign literatures may belong to azuki-type.
The
kind of myxosporidia is specific to the fish. The fishes which
are closely related share the same myxosporidia. These facts
5
,-, •
Wevl_pl.11,-
ge2ee
t,h,ee
: -,.,, ,,,e,r4
1,1. '-'..e•fL,---1
.
-
:w v.:,z7'.e,A,,,i:eg.",c;.1%
Z:,- ,.•:i+z
Phato. 1
.:M
Early stage of "azuki" in yellawfin (cross
section of the milscle).
1 9., s
1 0 11
'
Fig. 1
A: Hexacapsula neothunni isolated from "azuki" in
yellowfin tuna (frm katsumoto)
B: Chloromyxum thyrsite isolated from milky barracuda
(from Wills).
6
that myxosporidia is related to the/jellied meat éither directly
or indirectly:
Fig. 1 shows some examples of the spores isolated
from "azuki" of yellowfin tuna and "milky" in barracudas.
2) Sashi-type
This type has fluidified vacuoles in the muscle. The
vacuoles contain jelly-like substances.
The size of a vacuole
is as big as a faba bean. The vacuole may be found isolated
in the muscle or several of them may become clustered as the
'symptom advances causing an extensive destruction in the
muscle.
However, the destruction does not occur to the whole
fish as in the case of azuki-type, but the affected tissues remain
rather scattered in the muscle.
The spores of myxosporidia which were found in azuki-type
were not found in the sashi-type (in broadbill swordfish and
sk'ipjack).
Matsumoto (Tokyo Public Health Laboratories) states
that lack of the spores is the characteristic of sashi-type.
Since pearl-like and soft sprh^rical substance is often found in
the vacuoles in early stage of the symptoms, so called !'hoshi"
(or star) is thought to be ralated with jellification in sashitype.
I have observed jellification of the tissue around
"hoshi" in unfrozen broadbill swordfish which was left at about
20°C for 20 hours.
Tliere are two kinds in "hoshi", soft one and hard one. YOu
can tell them apart by touching them. Matsumoto identified the
hard one (probably in broadbill swordfish) as the sporangium
of the myxosporidia which belongs to chlorom}r.xum which is a
parasite of the fish muscle. He did not see, however, any
7
relationship between the hard "hoshi" and jellification of the
muscle.
Relationship between soft and hard "hoshinis not also
mentioned.
If soft "hoshi" is quite different from hard one
in nature, then what is hard "hoshi" which causes jellification?
"HOshi"-like substances (diameter 3
-
7mm) have also been
found in the muscle of 30 - 40% Of the salmon caught in the
north Pacific.
They have been identified aè the spoegium of
Henneguya salmicola. Though the muscle is not the only place
where the sporangium is found, the sporandium has been found.
in "sashi" (2 x 3mm).
Since the case with salmon will probably
belong t‘o sashi-type according to Patashnik's description,
the relationship between myxosporidia and jellification can not
be denied.
Since the jellification mechanisms or the causes of the
jellifiction are not known in the sashi-type jellied meat no
clear relationship is established between jellificatïôn 'and
myxosporidia. However, it is easy tojtell sashi-type from
azuki-type by their appearance. "Sashi" occurs in broadbill
swordfish, skipjack, silver salmon and sometimes in iellowfin
.
tuna.
.3) Fukuro-type •
This type of jellied meat occurs in halibuts and "fukurobirame"(or "fukuro" affected halibuts) is well known in Japan.
The skin is easily separated from the muscle dùe to destriction
of the muscle giving the appearance of a bag---this is probably
the reason for its name, "fukuro"(or a bag) (Photo 3).
Unlike .
the
Pazuki",fro-bame"lcksyxoprida.Hwve,
8
Table 1 Fishes reported to be affected by àzuki-type
jellied meat.
Fish
xbnormalitv
Sorozoa
yellowfin tuna
"azuki"
Hexaca-nsula neothunni
swordfish
"a zuki "
Chl.oromvxum musculoliguefaciens
barracuda
milky barracuda
Chloromyxum thyrsite
stockfish
milky stockfish
Chloromyxum sp.
hake
milky hake
Chloromyxum sti.
lemon sole
milky lemon sole
Ghloromuxum sp.
jellied meat
Neochloromyxu_m. cruciformum
flyingfish
jellied meat
dolfin
jellied meat
Pacific halibut mussy halibut
wormy halibut
(patty halibut)
Unicansula muscularis
r
Photo 2"Sashi" in bigeye tuna (cross section of the muscle)
9
Photo 3 "Fukuro-birame (from Matsumoto)
10
myxosporidia has been found in the messy halibut which is theht
to be identical with our "fukuro-birame".
Though myxosporidia has not been found in "flikuro-birame",
a possibility of finding it in future can not be denied. It
may also be true that there are several types in the jellied
meat in halibut, such as "azuki" and sashi" .(similar to those
in bigeye tuna and skipjack)and the type where the muscle is not
degraded (jellied American plaice), which will be discussed later.
But it should be proper to say at this moment that the jellied
meat in halibut, where tissue is degraded and fluidified, is
called "fukuro" in (ye country.
H. The type where the muscle tissue is softened without being
) Chalkiness
This is an abnormal muscle of Pacific halibut caught in
the Pacific.
The muscle of a chalky Pacific halibut is white
in color and very soft in severe cases.
The affected-muscle has 70 - 80% water content, whereas
that for normal tissue are 17 - 80%.
The amounts of protein
and fat in the abnormal tissue are 17 - 22% and 2.2 - 5.8%
respectively which are higher than those of normal muscle whose
corresponding figures are 12 - 18% and 0.15 - 0.59%.
What
causes this is unknown and there is no evidence that this is
a disease.
2) "Jelly" (jellied American plaice)
"Jelly" occurs in halibut.
The fillet which was affected
by this abnormlity is shiny and milky white in color and tends
11
to shake when touched by a finger.
The connective tissue of
the muscle becomes loose and the muscle is readily separated.
The abnormal muscle has 4% higher water content but 4% lower
protein (actomyosin) content than normal muscle.
intercellular space in the muscle.
There is
Myxosporidia was not found
in "jelly".
The cause for this abnormality has been considered to be
a result of protein consumption in the muscle during spawning
activities in cold water (-1 - 0 ° C).
ILIEnEEE.U121 "
This type occous frequently in large sized bluefin tuna.
The affected muscle ià reddish in color and has less fat. The
texture resembles that of a hard jelly.
The quality of "konnyaku"
muscle for "Sashimi"-dish (sliced fish eaten raw with soysauce
and Japanese horse-radish, a very popular dish in Japan*) is very
poor.
.
A skinny-looking fish (the Japanese often calls it scallion
bulb (Allium bakeri*)) usually belongs to this type. This occurs
during a short period of perhaps 20 days right after the spawning
then desappears as the fish recovers from the exhaustion.
Similar observations have been made on yellowfin tuna,
bigeye tuna and black marlin.
4) "Hotchari"
A salmon which has finished the spawning activities is
called "hotchari" (both male and female). Their muscle is soft
* Inserted by translator
•
12
and easily brakable.
this muscle.
Even the salting process does not harden
The muscle at the back of the'fish looks melted
in a extreme case.
Water content of the muscle of the affected fish is 10%
higher than that of normal fish but prôtein.content is about 7%
lowër.
The affected fish has less salt-soluble'protein (actomyosin).
The ratio of actomyosin over toatal protein is 39 - 40% for. normal
fish and 35 -38% for "hotchari". However, l'hotchari" dissolves
more easily in 10% NaCl solution (45 -46% for normal fish and
50% for "hotchari"), which makes "hotchari" unsuitable for salting.
Enzymatic activity for autolysis in the affected muscle (optimum
pH is 3.6, probably cathepsin D) is about 6.5 times higher than
thât in the normal muscle.
5) Muscle dystrophia.
This problem occorred in cultured yellowtail in the winter
of 1973.
The incidence was reported as a kind of jellied meat.
The mildly affected fish is skinny and blackish. The muscle has
lost its lustre and.comes off easily from the bone when pushed
with fingers. In more advanced cases the fish gets skinnier
and the muscle losses its elasticity. In very severe case the
muscle looks melted and becomes more transparent due to the
increased fat content.
The muscle also becomes separated easily
from the bone.
Histological examination suggests that the abnormality is a
progressive muscle dystrophia.
13
Causes of jellification,.
Since there is on1y a few reported cases where causes fpr
jellification are identified I had to classify—the jellied meat
according to its appearance. However, there must be a different
cause for a different type of jelliedmeat, namely type I where
the muscle becomes degraded and fluidified and type II where
the muscle becomes soft but not degraded and fluidified.
Among those which belong to the type I myxosporidia has not ,
been found in "sashi" of bigeye tuna and skipjack and "fukurcibirame", Myxosporidia have been found in many of other cases.
A myxosporidia has been specific to a species of fish.
These
facts suggest, as I had mentioned previously, that myxosporidia
is associated with jellied peat.
Wills stated that the :iellification.of the fish muscle was
a result of tissue digestion by a powerful proteinase secreted
by a myxosporidia.
However, the secretion of the prpteinase by
the myxosporidia has not been proven yet. Bis theory is doubted
by some because it can not explain the jellification in bigeye
tuna and skipjack and "fukuro-birame".
I do not think that there
is only one factor which causes all kinds of jellied meat which
belong to the type I. Tsuchiya has observed that the extracted
juice from "azuki" of swordfish had a higher gelatin hydrolysis
activity at pH 4 than that from normal muscle. Patashnik has
reported a proteinase activityjin terms of hemoglobin hydrolysis
activity, at pH 3 - 4 in the fluidified vacuoles of Pacific
halibut and lemon sole but not in the normal muscle around the
vacuoles.
Asagawa failed to notice a clear cut difference in the
similar enzyme activities in "azuki" of yellowfin tuna.
However,
I have observed that a proteinase activity was about 3.5 times
higher in any part of the muscle of a "-azuki" fish than in that
of normal fish. The optinum , PH‘for the enzyme activity was 3,
suggesOting that the enzyme is cathepsin D.
The fact that the jellied meat has a higher proteinase
activity supports the thecey of Wills. The question remains wheather
A
the myxosporidia secretoSthe proteinase. Once the proteinase is
isolated and charactzed the question would be resolved easily.
My own investigations have shown so far that the jellification is associated with cathePsin D-like enzyme. Jellification is
most severe in the
center of a fish and negligible in the sub-
cutaneous tissue and caudal portion, but enzyme activities were
high in any portion of the affected fish.
The difference in the degree of jellification at the different
part of the fish is due to the different rate of jollification,
which, in turn, can be explained by the different temperature
distribution of the fish.
The temperatures of subcutaneous tissue and caudal portion
of the fish immediately after being caught are close to that of
the sea water, whereas the temperature at the center of the fish
is several degrees ( Q C) higher than the water temperature. TIE
difference sometimes reaches more than leC.
The maximum
difference in the temperatures was 32°U. The temperature drops
very slowly in the center of the fish.
The above mentioned expanation reauires a hypothesis that
jellification occurs only after death.
The facts that no "azuki"
was found in yellowfin tuna right after being caught or those
15
of,
which were frozenee fishing boat support the explanation.
The following should be interesting as a research topic.
1) How does a myxosporidia (a foreign organism) increase the
activity of cathepsin which exists in the fish tissue (assuming
that the proteinase which showed a high activity in the jellied
meat is actually cathepsin D which exists in the normal fish
tissue).
2)Cathepsin may play a role in the softening of muscle of a dead
animal.
If that is true, what is it that becomes the substrate
In the muscle tissue ? The study may become more interesting
if it is done parallel
a similar study such as maturation
of animal meat or mec4ism of softening in the fish muscle.
The following is my own theory for the jellification in
azuki" of yellowfin tuna.
A proteinase, which may be small in quantity, first attacks
the connective tissue and a wall of cells (perimysium) which .
has an important role to keep the structure of the muscle tissue.
.
When they are attacked by the proteinase, though partially
r
it may be, the tissue structure becomes destroyed.. Then a bunch
of muscle fibrils is cut in places. This is the early stage of
jollification and the spots of fluidified vacuoles begin to show.
When this condition spreads to 1/3 - 1/2 of the entire muscle,
the muscle appears to be fluidified. Though the muscle seems
to be fluidified, more than 505 of the tissue is keeping its
original structure and the Protein molecules of the muscle fibrils
will not be brokendown.
No evidence is rerorted to support or possitively ammend
the Wills' theory for the cause of other types of jellied meat.
16: -
The causes for the ^ellifi cation of the type II jellied meat
were described above. "konnyaku" in tunas,
"jelly" in xmerican
plaice and "hotchari" in salmon were attributed to the muscle
softening caused by the protein consumption during the•snawning
activities.
A histological examination of AnÈrican nlaice s'nowed that
the muscle cells became thin creating space between cells, which
supports the theory mentioned above. however, if it is the case
how do you explain the fact that the consumed protèin was the
muscle fibril protein (actomyosin-type orotein) and not a water
soluble protein Y 'Nhy is it that the protein which constructs
the structure of the muscle fibre was chosen as an energy source
As it was reported that activity of a proteinase (-n?-o bably
cathepsin D) is high in "hotchari°", the consumption of the muscle
fibril -protein may have something to do with cathepsin. If the
muscle fibrils are cut and digested by a proteinase, the process
must be very orderly. Otherwise it would be impossible, once
they are digested at random, to restore the orderly structures
of the muscle fibrils and filaments. If our hynothesis on the
muscle softening during spawning is correct,'a relationship
between the sDftening process and
_ metabolic turnover of the
muscle proteins, especially the muscle fibril protèin, would
make an interesting research topic.
Jellied meat and food hygiene,
It is diff,cult for me to talk about general food hygiene'
Gt Yc
in relation to the jellied meat not only because therenmany
causes for jellied meat but also because I am not a f"ood hygiene
17
specialist.
Apart .from its taste, the physiological jellied meat such
as "jelly" in American Plaice, "konnyaku" in tuna and "hotchari"
in salmon is safe to eat.
Is it safe to eat the jellied meat caused by myxosporidia
without cooking it (i.e. in "sashimi")?
Since the practice of immediate freezing in the ship after
catching has become a standard the problem of "azuki" in yellowfin
tuna has disappeared from the fish market.
However the Potential
cause for jellification still exists in the muscle.
There is no
evidence that freezing will kill the myxosporidia.
Fortunately no one has reported so far that a myxosporidia
has caused a disease symptom in human. That is plobably because
the reported hosts of myxosporidia which include Uhloromyxum
henneguya are limited to fish and reptiles and no warm-blooded
animals are reported to be its host.
be regarded as safe to human.
Therefore, nyxosporidia may
But it is desirable to have more
positive evidence..
The research on the abnormalities of fish muscle has been
desultory and very shortcoming. Recently the fish market in
Japan is having a lot of "new faces" and it is Possible to have
a new type of muscle abnormality. It is desirable to have a
correct understanding of the muscle abnormalities by collecting
the available information and knowledge on the subject, which
will also enable us to prepare for the possible new problems.