According to Jewish law, all fish with fins and scales are kosher. The fish commercially sold as tuna fits into this category and may therefore be served in a Jewish home. Unlike meat or fowl, fish does not have to be slaughtered or salted.

However, you need to know that the fish in front of you is actually a kosher fish, and not the meat of a similar-looking non-kosher fish. (It is apparently common in the fish industry to substitute the meat of one fish for another. Also, many varieties of fish can go by the same name, even though one may be kosher and another is not.) This leaves you with two solutions:

  1. Purchase your fish from an establishment that is under rabbinic supervision.
  2. Purchase fresh, unprocessed tuna that still has the scales attached, ensuring that you are getting kosher fish. Ask the store employee to wipe the knife clean and cut your slice of fish on a fresh sheet of paper. You should then carefully wash the part of the fish that has been cut in water that is no warmer than room temperature.

All canned, smoked, pickled, or otherwise processed tuna must be certified by a reliable kosher agency.