Although sushi is on the whole a very safe food to eat, it is best to keep in mind a number of safety precautions when preparing and serving raw fish, as sea fish in particular can carry a number of bacteria.
Ensure fish is as fresh as possible when buying. With whole fish, check that eyes are bright and shiny and stand proud, rather than sinking in to the sockets. Flesh should be firm and spring back to the touch. The skin should also be shiny, with virtually no fragrance. Fillets should be firm, yet moist and appear freshly cut, with certainly no brown tinges.
When preparing, care must be taken to ensure that there is no cross contamination on chopping boards or knives, and work surfaces and utensils should be frequently and thoroughly cleaned. Once you have cut off a slice of filleted fish to use in a piece of sushi, it must never be placed back on the chopping board, as this may transfer bacteria to the serving dish. Sushi accompaniments such aswasabi and gari can also help promote hygiene.
Choose your supplier
In Basel area, the most reliable sources I found are the fish department in Manor, Globus or Migro Fishmarkt. I would always tell the fish seller it’s for sushi and he/she usually will gladly prepare a good piece for you. As for Salmon, I ask for skinless, it saves you a lot of time and hassle skining it yourself.
(Part Text source: http://www.eat-japan.com)