Thawing frozen fish for sashimi
I would not recommend Vixen's method. Here is how real sushi chefs do it. My wife is Japanese and we found several websites that explain (exact same way each website). You can go there and see for yourself if you can read Japanese. Anyway here are the steps:
1. Wash frozen fish with tap water
2. Prepare a bath of lukewarm (35-40C) water saturated with salt. It should be as salty as the sea. To confirm it is salty enough, the frozen fish should float, not sink.
3. Let the fish sit for 3-4 minutes. (it will not be thawed at this point)
4. Remove from the salt water and pat dry with paper towels.
5. Wrap the fish in paper towels and place in a plastic bag. Put in the refrigerator (15C) to thaw for about 5 hrs.
This will result in a finer color and better "umami" flavor.
Here is one of the Japanese websites.