Interesting tuna handling link

[Woody]

I know we think we are producing "Sushi Grade" Tuna by following our spike/bleed/chill/ice process, but would it pass the fish buyers test?

Tuna handling

[flapbreaker]

The link was slow so here is the text minus the illustrations.


INTRODUCTION
Sashimi is a traditional Japanese dish made from thin slices of premium quality raw fish. The most popular sashimi fish are the red meat
species, particularly tunas and skipjacks. “S ashimi” in fact means much more than just “raw fish”; the term implies specific requirements
regarding freshness, appearance, presentation, texture and taste.
Only genuine premium quality fish will fetch a good price on the sashimi market. Fish quality is determined by several factors, both
biological and non-biological:
• Biological factors such as species, age, size, degree of sexual maturity, and the presence of parasites or diseases, are not within the
fishing crew’s control. The size, species and stage of sexual maturity are very important because they influence the fat content of the
fish. The tuna with the highest fat content attract the best prices in the sashimi market.
• Non-biological factors are within the crew’s control. They include fishing method, and handling and chilling techniques used
after capture.
There are many ways of handling and packing fresh tuna, but only a few are suitable for exporting high-grade product to sashimi markets.
This booklet is primarily intended for crew members on tuna longliners, and attempts to describe in detail a handling and refrigeration
method that meets the exacting standards of the export fresh tuna market.
For certain stages of the handling process, alternative techniques are described because requirements may vary from importer to importer.
It is therefore essential that the fishing boat operator be aware of his buyer’s specific requirements.
Some fishing boat operators export to several international markets (e.g. the largest and highest-grade tuna are exported to Japan,
while others are exported to Hawaii or the US mainland); crew members may therefore need to handle each fish according to its
intended market.

THE ESSENTIAL TOOLS
Before hauling in the longline, the crew should prepare the necessary equipment so that the fish that will be hauled aboard
can be dealt with quickly.
• gloves, preferably cotton or nylon, for all handling purposes,
• two gaffs, to haul the fish aboard,
• a mat, a carpet or a foam pad to lay the fish on,
• a club to stun the fish,
• a spike to kill it,
• lengths of monofilament nylon or a stainless steel wire to destroy the spinal cord (“Taniguchi” method),
• a drop blood knife, with a very short blade, to bleed the fish,
• a sharp knife to gill and gut the fish,
• a stiff brush to scrub out the gill cavity,
• a seawater hose, to force the bleeding of the fish and to rinse away all blood and slime,
• elasticised cloth sleeves (or “socks”) or plastic body bags to protect the fish once in the slurry (chilled sea water - CSW) or in
the refrigerated sea water (RSW).

GAFFING AND LANDING
The tuna’s external appearance is one of the important factors that determines its market value. Always treat your fish with great care and
always wear gloves when you are handling it.1
• Always gaff the fish in the head (Fig. 3).
• Never gaff the fish in the body, the throat or the heart 2 (Fig. 4).
• Use two gaffs for big fish; insert the second gaff in the mouth (Fig. 5).
• If the boat doesn’t have a gate in the bulwarks, it is advisable to lift the fish by the tail to help haul it on board.
• The fish should be landed on a foam pad, a carpet or a mat.3
• Take care to fold the pectoral fins under the fish so that they are not damaged, especially when turning the fish from one side to
the other.
• Carry out all subsequent handling on the foam pad, carpet or mat.


KILLING
On arrival at the export market, each sashimi-grade tuna will be very closely inspected. Fish that have not been killed in the way
described below will be down-graded, and will lose value. To avoid this, the brain and the central nervous system (spinal cord) should
be destroyed in all tunas potentially exportable as sashimi-grade (yellowfin and bigeye w eighing over 25 kg).
Once aboard, you should kill the fish immediately:1
• Stun the fish with a sharp blow to the top of the head (between the eyes) using a fish club or other blunt instrument (Fig. 6).
Alternatively, you can calm a fish down by covering its eyes with a gloved hand or a piece of cloth.
• Use the fish club to remove the hook from the fish’s mouth.
• Stand over the fish, steadying it firmly with your legs braced just behind the pectoral fins.
• Locate the soft spot (Fig. 7) by running your thumb over the top of the head, between the eyes.
• Insert a spike into the soft spot at a 45° angle and push it down into the brain cavity. If the spike is inserted in the right place, the fish
will give one last shudder (the body will quiver, the mouth will fall open and the first dorsal fin will spread) before going limp (Fig.
8). If this does not happen, the soft spot should be spiked again.
• Move the spike around (to destroy the brain) until the body stops moving and the jaw goes slack. Make sure you don’t push the spike
too deep as it could damage the entrance of the neural canal.
• Some operators use a coring tool to destroy the brain and make a hole for the Taniguchi wire or nylon monofilament. The coring tool
is usually struck with a mallot

KILLING (continued)
It is advisable to pith1 the fish (Taniguchi method) after killing it:
• Insert a length of rigid monofilament nylon2 or stainless steel wire into the brain through the hole made by the spike or the coring
tool, and push it as far as possible into the neural canal to destroy the spinal cord (Fig. 10). The fish should quiver again as the
Taniguchi tool goes down the neural canal.
• If using monofilament nylon, leave it in the neural canal, but cut it off to leave the last 2–3 cm emerging from the fish’s head3
(Fig.11).

BLEEDING
Bleeding the fish immediately after killing it1 improves the appearance of the flesh2 and extends its shelf life3. This is a vital stage for the
quality of the fish and its subsequent value on the sashimi market.
• Bleed the tuna by making a cut in its sides with a short-bladed knife, five to ten centimetres behind the base of the pectoral fins. The
cut, two centimetres deep at most, should be made perpendicular to and across the pectoral fin recess4, on both sides of the fish (Fig.
12). Blood should flow freely from these cuts.
• Leave the fish to bleed for three to five minutes. We recommend this bleeding technique for tunas exported to Japan.
• To accelerate the bleeding process, you can make a cut in the membrane between the gill collar and the gills. Place a seawater hose
in this cut to accelerate bleeding and rinse away all blood from the gill cavity (Fig. 13).
• Alternatively, use a hose with a short length of sharpened stainless steel pipe inserted in the end. S hove the pipe into the gill cover in
the region where a cut would normally be made. The pipe makes a hole and a seal to pressurise the gill cavity (Fig. 14).
• Another bleeding technique involves making a cut in the throat just in front of the heart and putting the seawater hose in the mouth.
Blood should flow freely from the throat cut (Fig. 15). This technique is acceptable for tunas exported to the US mainland and
Hawaii.
GILLING and GUTTING
The internal organs (intestines, gills, kidneys, etc.) contain bacteria that accelerate the deterioration process in fish. T hey should
therefore be removed as quickly as possible, in order to extend the fish’s shelf life.
• Make a cut, 5-10 cm-long1, in the fish’s belly, up to 1 cm in front of the anus. This cut should be made in the direction in which the
scales lie, in other words, towards the anus (Fig. 16).
• Pull the digestive tube through this cut.
• Cut off the end of the digestive tube near the anus (Fig. 17).
• We recommend another method called the “donut” cut. It involves making a circular cut around the anus2 (Fig. 18), without severing
the digestive tub. The resulting plug or “donut” is then pushed into the gut cavity.
• Insert a knife behind the gill cover and cut towards the eye until the knife hits bone (the skull) (Fig. 19). Repeat the procedure on the
other side3.

GILLING and GUTTING (continued)
• Cut the membrane between the gills and the gill collar along its whole length on both sides of the fish (Fig. 20).
• Cut the connection between the gills and the lower jaw (Fig. 21). Do not cut the connection between the throat and the lower jaw
(the isthmus). If this is cut or broken, it must be tied back to the jaw, using a short piece of line or rope, otherwise gaping1 will occur.
• Cut the connection between the gills and the base of the skull (Fig. 22).
• Remove the gills and internal organs in one piece through the gill opening (Fig. 23). This stage is sometimes difficult because of the
membranes connecting some organs to the abdominal wall. Remove the heart.
• Rinse thoroughly.

CLEANING
• Carefully cut the membrane attached to the gill collar. With the knife, scrape the edge of the collar until you get down
to white bone1 (Fig. 24).
• With a stiff brush, scrub the base of the skull and the vertebrae to remove all coagulated blood and kidneys (Fig. 25).
• Cut off all loose pieces of flesh and tendons inside the gill cavity.
• Carefully rinse the fish, inside and outside.
• Some buyers request that the long dorsal fin and anal fins of large yellowfin tunas be cut off at their base using a saw-edged knife or
a saw2 (Fig. 26).
• The fish is now ready to be iced (Fig. 27).
• If slurry (CSW) or refrigerated seawater (RSW) are used, the fish should be protected by an elasticised cloth sleeve (or “sock”) or a
plastic body bag 3 (Fig. 28).

ONBOARD STORAGE
Tunas are the most evolved species of fish in that they control their internal (body) temperature1. This internal temperature can even rise
to 30°C+, for short periods of time, under certain conditions (e.g. during a feeding frenzy or during capture). In order to keep the fish in
pristine condition, the internal temperature must be lowered as quickly as possible to 0°C and then maintained during onboard storage,
unloading, packing and transport.
To obtain a top-quality product, we recommend using the following two-stage procedure:
• Lower the internal temperature of the tuna by placing it in a slurry of flake ice and seawater (2 parts ice to 1 part seawater).
• After 24 hours, transfer the tuna to the fish hold and ice it. No further handling is required until you arrive in port.
Slurry or chilled seawater (CSW)
The main advantage of the chilled seawater is that the entire surface of the submerged fish (including the abdominal cavity) is in direct
contact with the cooling medium. This is the most efficient technique for rapidly lowering the core temperature of the fish.
• To prepare a slurry of flake ice and seawater in a fish box, use a ratio of 2 parts ice to 1 part seawater.
• The length of time the fish should be left in the slurry depends on its size: 6–12 hours is advisable for the smallest sashimi tuna (25
to 40 kg); larger fish should be left in the slurry longer (up to 24 hours) to be sure that they are chilled to the core. Although fish can
be left longer in the slurry, we recommend removing them after 24 hours at the most, otherwise their colour will begin to fade and
their eyes will go white.
• Use a large (2 m3 or more) insulated box with several compartments and a drainage hole. In heavy seas, the compartments will help
reduce the rocking of the fish inside the box. It is advisable to have two slurry boxes on board.

Some comments and advice
• Before placing them in the slurry, each fish should be individually wrapped in a cotton gauze “sock” or in a plastic body bag with
holes in it. This avoids damage caused by the fish rubbing against one another. This sock or bag is removed before the fish is packed
for export.
• Adding salt to the brine lowers the temperature by several degrees and makes it possible to chill the fish more rapidly. The
temperature of the slurry should not be lower than -2°C, temperature at which the fish start freezing.
• Check the slurry regularly and add ice whenever necessary. Stir the slurry often to keep it well mixed and to avoid pockets of
warm water forming.
• Too little ice in the slurry leads to poor cooling and loss of quality.
• Too many fish in a box also leads to poor cooling and loss of quality.
• A probe thermometer measures the fish’s core temperature (the temperature of the meat immediately surrounding the backbone). We
recommend using one as it makes it possible to check the core temperature regularly in order to transfer the fish to the hold at the
correct time (transfer to the hold should take place when the fish’s core body temperature is near 0°C).
Icing
• When the fish have been sufficiently chilled (0°C at the centre), they must be removed from the slurry box.
• Carefully transfer the fish to the fish hold. Avoid gaffing the fish, dragging them along the ship’s deck, or damaging their eyes.
• Cover the fish with ice in successive layers (a layer of ice, a layer of fish, a layer of ice, etc.). Whenever possible, have no more than
three layers of fish (otherwise, the fish at the bottom of the hold may become damaged from the weight of the ice and other fish
placed on top of them).
• The heaviest fish should be placed at the bottom of the hold.
• Once in the ice, no further handling is required until the unloading.
• Fish prepared in this way (placed in slurry, then stored in ice) can be left in ice for up to two weeks.

OTHER METHODS OF ONBOARD STORAGE
Direct icing
Some longliners do not use a slurry, but instead, ice their catch immediately. C ontrary to chilling in a slurry or in refrigerated seawater
(RSW), this method does not require the use of a gauze sock or a plastic body bag to protect the external appearance of the fish. S ashimigrade
tuna can be kept on ice for up to two weeks.
In order to use this method properly you should:
• Place one layer of fish, belly downwards, on a thick layer of ice. S urround each fish and fill its gill and abdominal cavities with ice.
• Avoid piling up more than three layers of fish.
• Avoid placing fish in contact with the edges of the fish box (or hold) or in contact with one another.
• Eliminate air pockets1 after 24 hours by repeating the icing procedure.
Refrigerated seawater (RSW)
Some longliners are equipped to store fish in refrigerated seawater (RSW). The water in a RSW system is usually a mix of 80 to 90 per
cent fresh water and 10 to 20 per cent seawater. S ashimi-grade tuna may be kept in RSW for up to two weeks.
• Monitor the temperature in the RSW tank several times per day, either with a built-in temperature gauge or with a handheld
thermometer. Temperature must be kept between –0.5° and –1°C.
• Protect the fish with a gauze sock or a plastic body bag.
• Place it carefully in the RSW tank so it doesn’t get damaged on the sides or bottom. Usually, a long tail rope is used to gently lower
the fish until it comes to rest (Fig. 29).
• Some RSW boats suspend the fish vertically in the tank by tail ropes (Fig. 30). Other boats have tank baffles so that fish’s movement
is minimised. No further handling is necessary once the fish are placed in a RSW tank.

UNLOADING
These rules should be followed during unloading.
• Do not twist or bend fish when removing them from the ice, as there is a risk of making the fillets an odd shape, which causes gaping
and damages the fish’s external appearance.
• Handle fish gently. Do not throw them or drag them along the deck or the ground.
• Do not leave fish too long in the open air or sunlight. P ut fish on ice or pack them for export as soon as possible.

[5 Salt]

Interesting Read - I must be the only one not fishing today.


I wonder what the logic is behind pithl (Taniguchi method) - running heavy mono into spinal cavity - is?

[Ling Sling]

I was curious of the same thing. The footnote on the pdf said that it stops certain biochemical reactions that can lead to flesh deterioration, but I wonder if it would make that much of a difference for a fish that was quickly cooled. It seems like that would make the most difference.

[judyfish99]

How interesting!! Since there is no illustrations, I would like to see in person how this is done...I think I will go for sushi today :grin:

[corrirod]

Hey Judy, there are illustrations if you click on the link on the first post.

[judyfish99]

Thanks, corrirod!! :grin: Lack of sleep here..had to use the broom handle ceiling trick on the upstairs neighbors at 1:15a. :depressed:

[Mark Mc]

The wire in the spine completely shuts down the central nervous system. Otherwise, the temperature regulation system is still pumping out enzymes (trying to regulate temperature). The enzymes create histamines which cause spoilage.

[Orca]

What size mono are we talking about here? Something like the heavy string trimmer cord?

[skein]

Last year I just left my bled and gutted fish in the slurry unless I needed to make room for more fish, at which point I filled the body cavity with ice and layered them in the tote, putting ice all around and on top of them. I was admonished to not leave them in the slurry as the water could effect the taste. Sounds like it may be all right after all.

Another thing I'm probably going to do this year is wait until the next morning to cark them. On the good tuna days the carking stations are usually plugged up and often it's way after dark by the time the fish are taken care of. I watched some guys leisurely carking their tuna about 10:00 one morning, and realized they not only were rested after the day before's battle, they had the carking station to themselves. Sweet!

Skein

[ron m]

Thanks for the link, some interesting info in this, anything we can do to make the quality higher is a good thing to know. I now know a better way to bleed them, also will handle even more carefully. How many of us have a "tuna rug" for our deck? Yeah, I hear it coming, some folks want tuna so thick on the deck that they have a crpet of tuna!

ron m

[Boatdog]

Ummm, uhhhhhh, duhhhhhhh, slobberrrrr.... after "stirring" their brain with a spike, is the string/wire "spinal-ectomy" really necessary? you mean after that they're really still trying to regulate temp? Seems like a losing battle in a chill tank. Especially for a 20-40 pound immature Albacore. I'm not a commercial Sashimi grade TUNA provider, but that is another level of perfection. I know I ain't perfect.

The information was very interesting however!

[Double G]

Skein, my tuna mentor in Florence taught me that you always wait until the next day to cark tuna since the colder they are the better. Being well past 50 (closer to 60) it appeals to me since I'm damn tired after a day at sea.

Thanks for all your input here on ifish.

[Woody]

Last year, I kept one gutted, gilled, fish to show off to some buddies at work. I kept it packed in ice for about 48 hrs. When I finally did get around to carking it, it was cold to the bone, so cold it hurt. It was MUCH easier to loin and skin than a fish fresh off the boat. The flavor was just as good and the texture was firmer.

[ron m]

--

[tracker]

Woody I hope you read the most important part! It states to use a gaff or two. On the other hand it does say to gaff in the head. I read nothing in there about yarding them in!