I was sure if he ran a restaurant, he'd be cited for health violations by not using sushi grade fish for sashimi, but after a Google search, it seems that no one - not the FDA, not local health inspectors, not any governing body - knows what sushi grade means! Yep, there's no regulations, as long the fish has been frozen for a period of time to kill parasites. I suppose it's comforting that even when self-regulated, at least seafood vendors care about whether we get tapeworms.
Basically, "sashimi" is just a sexy marketing term to mean any fish that can be eaten raw. Of course, the fresher the fish, the better the taste and texture, so these fish should be killed and iced ASAP. Here's more info from Sushifaq, Cooking Stack Exchange, and Beyond Salmon.
After more Googling (yeah yeah, so I trust online strangers' opinions more than my own boyfriend's) using Costco fish for sashimi is not uncommon. From personal experience, their salmon quality is actually quite decent. B is very picky about the package date being the same day to ensure absolute freshness, so he only trusts Costco (Ok, I know this is the second post in two weeks waxing eloquently about Costco, but my boy is in love with that place), and does not recommend getting the salmon from any random Chinatown market.
Update to some FAQs in the comments: The salmon is fresh (not frozen), and the day you buy the salmon should be the day you make this recipe - don't let it sit in your fridge for days!
N: I want you to make this salmon sashimi for my family when you visit us!
B: Oh you know how to make sashimi now, so you can do it for them.
N: Well, I'm afraid I'll poison them, so I'll let you make it!
B: Great, so if anything goes wrong, I'm the fall guy, eh?
The Gentleman's Sashimi
fresh salmon filet (check the packing date - the day you buy = packing date = day making the recipe)
salt, to rub
rice vinegar, diluted in water (optional)
1 sushi cup rice, recipe below
Rinse and rub a generous amount of salt onto your salmon (both sides). Let sit in fridge for 2 hours. Afterwards, take out salmon from fridge and rinse with water.
Submerge your salmon in diluted vinegar (preferably rice vinegar but white works as well). You use pure vinegar or dilute the vinegar up to 1:10 (ie 1/2 cup vinegar and 4 1/2 cups water) if you want a less vinegar taste.Let sit in fridge for 1 hour. Remove from fridge and rinse thoroughly.
Pat it dry. Wrap salmon in saran wrap and put it in the freezer over night
The day you want to eat it, remove it from the freezer and let it thaw in the fridge. This should take 6-8 hours; do not try speed it up by leaving it outside. Cut the sashimi with a sharp knife in a slicing motion. Mold rice with your hands, dab with wasabi, and cover with your sashimi.
The Gentleman's Sushi Rice
This serving size here is for 1 person. The lady and I do not like too much rice in our nigiri.
1/2 cup sushi rice
1/2 cup water
1 tablespoon rice vinegar
3/4 tablespoon sugar
1/2 teaspoon salt
1/2 tablespoon mirin
Rinse the rice only 3-5 times (water does NOT have to run clear) and drain in a strainer. While rice is draining, combine vinegar, sugar, salt and mirin together in a bowl and mix well.
Add rice to the pot. Bring quickly to a boil and then reduce to a simmer.
Cover the pot and DON'T touch it until the end, NO PEEKING. Put something heavy on the lid like another pot. The more pressure the rice is cooked under, the better it tastes.
Cook for 15 minutes before removing the pot from the heat but keep the lid CLOSED. Let rice rest for 10 min and then remove the cover.
Place in a glass dish to cool and lightly fan the rice while adding the vinegar mixture. Mix rice gently, being careful not to break it. Enjoy!
Doc Uy's notes: As a caveat, Costco does not claim to sell sushi grade fish, but if you freeze it per FDA guidelines (pg 69), you should be ok from parasites. As a doctor in training, I must also recommend taking FDA precautions if you're pregnant, old, sick, etc! Please be diligent in making sure your fish is good quality, don't eat fish that has never been frozen, and treat the fish with salt and vinegar for safety.