Dear Kosher Spirit,
In a previous issue of Kosher Spirit (Tishrei 5768), the article on kosher fish mentioned that not all varieties of tuna are kosher. How is this possible and what varieties are not kosher?

The OK responds:

Depending on where you are in the world, fish names are surprisingly interchangeable! In one country a certain fish is called “tuna”, while in another country it is called “mackerel”. This is especially common in the “cod” family of fish.

Tuna, mackerel and kingfish are part of the same family of fish species. A specific mackerel, called “snake mackerel” is NOT a kosher fish, but depending on the country, it may be referred to as “mackerel” or “tuna”. In addition, many fish in the tuna, mackerel and kingfish family have scales that fall off as the fish leaves the water, making it very difficult to discern the kosher status of the fish.

Therefore it is important to buy only tuna with a reliable kosher certification and mashgiach temidi.