costco is mass produced food. The fish for sushi should be wild (not farm raised) and not frozen and then thawed. I doubt they have this at Costco and I wouldn't trust the 'consume by' dates as they won't reveal when the fish was last swimming, just the last day you can eat it before it makes you sick. The whole art of sushi is having the freshest ingredients. You should go to your local fish market and find cuts of fish that have been flown in that morning. You have to be very careful of bacteria. Do lots of google searches for how to prepare Sashimi (as the sushi ones skip over where to get the fish from) to find out what kinds of fish are the safest and how to slice them. If you are freindly with your local sushi chef talk to them. It's an ancient craft that takes years to really master. Not that you can't do it for parties, just that it's not as simple as getting an OK piece of fish and slicing it up. Whole Foods is not a bad choice either. Ideally buy the fish from the Asian department at WF not the fresh fish section as the sushi is different. What can be delicious if you can get very fresh fish is Tuna, Yellowtail Tuna, Salmon, and Swordfish. Also, you need a VERY sharp knife, preferably a Sashimi knife and the general rule is that the harder the flesh of the fish is, the thicker you need slice it (eg: Swordfish 1/16th of an inch).
