Don Tuma
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Joined: 4 November 2006
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Re handling freshly caught live tuna (the Scombridae Family). The Japs seem to have perfected a technique that others might do well to copy. Here is the sequence:
1. A live tuna is decked and de-hooked, the gill arches severed and a shallow cut made either side of the caudal peduncle (near the start of the tail fin). This means that the arterial pathways are opened at head and tail.
2. The live tuna is then placed into an open tank big enough to allow the fish to swim while fresh seawater is pumped into the tank causing it to overflow onto the deck and out the scuppers. This allows the fishes heart to pump the blood out of the muscle tissue while actively using the muscles employed in swimming. The amount of blood lost in this way is nothing short of amazing.
3. After 10-20 minutes, depending on how busy the crew may be, the fish or fishes are taken out of the tank. The head is left intact, but the tail lopped off at a point where the tail base is about 2-3 inches in diameter. The head is left on and punctured centrally, slightly above and behind the eyes. A fairly stiff wire about the diameter of a common coat hanger is inserted into the head and fed down along the spinal column sheath that contains bundled nerve endings. This nerve-stripping process causes all kinds of obvious involuntary muscle spasms, the effect of which not only delays the onset of rigor mortis, but diminishes the extent to which it occurs. At this stage the fish is regarded as "moribund" which I suppose is equivalent to being clinically dead or something like that.
4. The fish is then hosed and scrubbed clean with special attention paid to removal of the gill arches and their branchiae. Next is the first stage of the freezing process that removes the latent heat from the fish by contact with an ice-slurry bath. The second stage takes the fish down to -18 C, presumably by air-blast freezing, and the third stage further reduces the temperature to around -30 C. I am told that the quality of such fish when thawed at the central Tokyo fishmarket is unsurpassed.
The best methods of chilling and handling fresh, live finfish is somewhat less involved than for the tunas. Here is the procedure that I would recommend based on observing heaps of commercial fishers at sea:
1. If the fish is large (difficult to handle) don't let it bash itself about on the deck. Organise a killing box or tub of some kind where the fishes head, at least, can be held under water. Cut gill arches and let the fishes heart do the job of bleeding out. Next is the iki-jime trick using a spike or carpenter's awl to penetrate the brain. You'll know from the muscle contractions when the brain has been zapped.
2. Immediatly after iki-jime, place the whole fish into a slurry of freshwater ice and seawater. The usual proportions are 1 part seawater to 3-4 parts flaked or crushed ice.
Leave the fish immersed (covered) in the slurry for 1 to 1.5 hours. This is sufficient to chill the flesh of most species down their backbone. Large, thickset species like rockcod or grouper may take longer. Use a thermometer to check that the slurry temperature is maintained between -1 and 0 degrees Centigrade. Add more ice/seawater as necessary. Don't worry if the slurry is discoloured by blood after awhile, it matters not.
3. After chilling you can pack the whole fish in ice for transport to land or process the fish to whatever stage you wish. If you are filleting or steaking, remember to separate flesh from direct contact with ice by a layer of gladwrap or whatever.
Remember that it is the meltwater of ice that does the cooling, if the ice isn't melting, its not cooling the fish. Drain used meltwater out the scupper while travelling, unless you're into catching sharks.
4. Some species need to be kept separate from others because of their ability to produce endless amounts of mucus or slime even after death which seems to signal the mucus cells to go into panic mode. These guys are best filleted and skinned straight away.
5. I should mention that not all species of fish benefit by the same degree because of having been bled at point of capture. Certainly all pelagic species must be bled and also other swimmers that build up lactic acid in their musculature. I've never seen fishers take the time to bleed estuarine species like whiting, bream, flathead, garfish etc etc. and I doubt whether it would have any affect on the quality of their flesh provided they are otherwise properly handled.
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Iki Jimi - how does it affect the flavour ? - 
RE: Iki Jimi - how does it affect the flavour ? - 
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