I've heard the argument that since everything in sushi is raw (assuming there are no non-kosher ingredients), and that since the rice is cooked in a rice cooker that is used only for rice, it's OK to eat. Is this true?
This article by the CRC discusses this issue at length.
In short, the answer is: No, it is not okay to eat non-certified sushi. See the article for details, but some of the problems include:
- The sides, such as wasabi, soy sauce, and pickled ginger are suspect (for artificial coloring, manufacture with non-kosher products, and utensils used with davar charif respectively, along with other concerns).
- Cooked rice requires bishul yisrael, which must be certified.
- There is a possibility (albeit unlikely) that a certain type of seaweed paper for which bug-infestation is common, was used.
- The fish may have been soaked in brine to preserve color and flavor.
Per the CRC-Chicago.
There are various halachik questions in relation to Sushi and why you may not buy even raw Sushi from a non-certified establishment.