Pretty sure most of the japs eat frozen tuna sashimi, its just whether you reckon the handling was up to scratch for sashimi.

Most Sashimi you get commercially have been frozen. Its the handling chain thats the concern. If it is labelled as Sashimi grade then should be OK.

Its pretty hard to cut tuna neatly when fully defrosted. I place mine in the freezer until just half frozen, firm and with a japanese Sashimi knife (Just a Mundial one - not the true ones, I think they start at some ridiculous price) it does a very neat semi-pro job.

If it is your own, you know what you have done to it, so if you where messy, dont do it. If you prepared it hygienically from the start it is just the freshness you are bothered with. Freezer time spoils good sashimi.

Neels

This is the stuff we caught the other day. it was bleed right, guts out, on ice straight away and put in the freezer yesterday after a night in a slurry. I just rather eat it raw than cooked. If we defrost it, should that be done in the fridge over a few days? or on the bench for an hour or so and cut it semi frozen then?

If you want to eat it later, defrost in the fridge. If you want it soon defrost it on the bench, or even in water provided it not in direct contact to "wash away the flavours".

I get Sashimi grade Tigers from the Fishtruck here in karratha. If I want some tomorrow I let it defrost O/nite in the fridge, want it tonight, bench, want it now Water. By the way this Sashimi grade tigers if you can get some is spectacularly nice. Piss easy to prepare and delicious Raw.

 Some countries (I think Canada may be one?) require all sashimi to be frozen for health reasons (i.e. to kill parasites). From the YFT i've had vac packed and frozen, I cant say it looks all that nice frozen, let alone thawing it for sashimi...
May snap freeze the ones where its required by law though?

90% of fresh tuna sushi and sashimi in Perth is frozen before being used here, We get bugger all fresh sushi as the price of a fresh YFT fish is mega times the price of frozen sashimi portions to a top resturant.

It's all in the bleeding and chilling straight after capture that makes the difference.

Me, I spike the spinal collumb after cutting the head off ASAP and straight into a slurry ice bath to cool off the meat, then slice the pieces into strips about 1 inch x 1inch by 5 icnh in length, vac pack and freeze with in less than 6~10 hours of capture, then they defrost perfect. When defrosting, keep in the fridge on top shelf and let it defrost that way. Not in sunlight or under heat.

You'll be fine. I have a bit of frozen YF and Dogtooth that has been cryovaced and is the reserve when I haven't had a chance to get out. As long as it has been looked after in the boat (and by the sounds of it it has) it will taste every bit as good as straight off the fish.

the japs freeze their bluefin to about -50 using 2 stage compressors etc, as the more oily (read expensive/tasty) tunas otherwise dont freeze well.

This is due to the oils not completely freezing at -20 and hence turning rancid over time. Less oily tunas such as yellofin freeze ok such as how Tony has said.

Proper commercial kill/process technique is-

1/ Land fish as quick as poss

2/ 2-3 fingers behind pectorals, pointy knife in about an inch

3/ some do a small cut just in front of the tail

4/ Stand it on its belly, make a hole in the forehead with an apple corer type tool and feed a 5mm braided SS wire down the spinal cord to tail to kill all nerves.

5/ On its side lift gill plate and make a one inch cut deep at about 5o'clock in the shinyish bit near heart.

6/ inside small hose/deckwash into cut at heart and pump all the blood out of the fish, takes a couple of minutes

7/ 40mm circle cut around asshole, push it in with your finger :-)

8/ cut gills from carcass, push guts free from cavity and pull all out through gill plate in one piece

9/ scrub cavity, chuck a bit of ice inside, place in slurry.

Doing these for yourself of course this can be much simplified as Tony showed than if you need to show it to a Jap. The bleeding part if youve got a deck wash is interesting-if anyone is interested I'll post a pic of the correct spot for the cuts?

Yellowfin up north especially get very hot inside from vigorous activity on the surface and "cook" themselves from a long fight. Having said that only the japs would really notice and then to beat you down on price.

Thawing seafood safely should be done in a temp less the 4.5 (i forget exactly but its around there) degrees. its a slow process but i was told it was safe. Health department came into my shop and gave me info on all that as I have to thaw my seafood everyday for my business. Apparently washing up surfaces like prep areas without cross contaminating food with chems like sprays and detergents, ideally you're supposed to wash and rinse with 75 degree water. I learnt that too =)