The first point here is that bad fish, fish that could give you an intestinal parasite or a bad case of food poisoning, is not considered bad sushi.
It is considered impossible sushi.
Seriously. If you ever eat sushi which makes you sick, don't ever go back to that purveyor again. It doesn't matter if this was "just once"--if a sushi restaurant ever makes people sick, it has forfeited its right to a second chance.
If you really want to be well-liked on a karmic scale, you might call your local Board of Health and make a complaint as well.
It should be said that I have been eating sushi at least three times a month for the past 27 years, and, although my stomach is not particularly iron-clad, I have never--gulp--so far--knock wood--gotten sick from sushi. And I eat supermarket sushi and Teriyaki Boy sushi.
I make my own sushi at home, of which I can proudly say that the rice tastes good, although nothing like the rice in sushi restaurants. But I never feel that I am capable of detecting "borderline" fish--like the marvelously fresh and plump specimens you see in New York's Chinatown, or in the fish markets out on the boroughs. Fresh and plump, yes, but suitable to be eaten raw? I just don't know. I do indulge in a tuna steak or a salmon fillet from these places, and especially a couple of low-priced lobsters when possible. But I cook these fish pretty thoroughly before I eat them.
In markets where there is an English-speaking person to answer questions, I always ask if any of the fish are sushi grade.
If the person says, "Sure, all of them," then he or she has misunderstood the questions. I have never heard of tilapia being served raw, although I don't know why it shouldn't be--but that's the whole thing--I don't know. Also, it's not possible that all the different types of salmon will be sushi grade; some come from further away than others. Some fish come from enormous fishing boats with cleaning and freezing facilities on board; these are the source of most of the sushi-grade fish you'll find in restaurants or markets. Oh, and I don't think I've ever heard of fresh trout being served as sushi. Or swordfish.
A good fishmonger will say, "The tuna's sushi grade, and the salmon fillet." Or he might say, "Nothing today." Don't argue with the man; he's the pro. Worst comes to worst, you can always boil the shrimp and use that.
Last night my Beautiful Daughter and i want to a new sushi restaurant in the neighboring townlet of Rhinebeck, NY. We had eaten there previously and had found the restaurant, which specializes in "Benihana"-style grillwork as well as sushi, to be a little over-elegant for the town, but the sushi chef was attentive and the sushi itself was very good.
Well, last night was realized that "over elegant" was actually "overextended". Maybe this resto will make a go of it as a hibachi joint--two or three table were filled with chefs flipping beef and customers ooing and ahhing at the show.
The sushi side of the operation was just plain sad. Along with the usual place-settings of soy sauce bowl, chopsticks, chopstick rest and wasabi dish, each seat at the sushi bar featured an individual Glade air freshener candle.
I am not making this up, and I don't even want to belabor the point. Sushi can be very bad without smelling very bad, but restaurants really shouldn't have ANYTHING in them that smells that bad. So the BD and I were a bit shocked, but we hid it well and ordered shrimp sushi and salmon sushi for her, and tuna tartar for me.
Both were okay--that is, they didn't make us sick, and they had a nice presentation--but the fish was nothing special. Not any deep flavor, special seasoning, exceptional richness or mouth feel. It was all very bland--except the seasonings, which were too harsh. It was mere fodder, at about $20 for the lot. And that IS a lot.
Three guys came in and sat next to us, and we started to feel sorry for them. Perhaps they noticed the Glade candles before we did, but something seemed to make them suspicious before they even ate anything. Was it the fact that all the fish was pre-sliced and saran-wrapped in the fish case? (This means that it's not as fresh as you might like, and that the chef who puts together the sushi is probably not trained well enough to slice the fish himself. Or that the proprietor really, really wants to limit the amounts of fish used per order.) The asked the chef what he recommended, and he said, brightly, "Bass?" Like trout and tilapia, bass is just not a sushi fish--and I thought it was endangered, anyway.
Then the chef asked the guys, "You use wasabi, in your soy sauce?"
The guys said, "Doesn't that destroy the taste of the fish?"
Well, it does, actually. And we all ought to know that. Especially those of us who are, you know, professional sushi chefs.
By that time Tracy and I were finished with our dinner, so we were leaving. We felt the other patrons might be close behind us.
So this is how a sushi restaurant fails--and, incidentally, how it succeeds, as well. Of course the fish is going to be fresh; that's not even a point. The restaurant also needs to have an imaginative and well-trained chef, access to fish which actually tastes good, and an absence of objects which give the impression that without them you'd be keeling over from the stink of the joint.
I don't think that's actually too much to ask.