Muslims that follow the dietary restrictions of their religion, Islam, are forbidden from eating certain types of food. Often guidelines in the holy book the Koran are quite clear as to what is considered 'clean' to eat or not. However, with the emergence and spread of new types of food, it can become confusing what is considered acceptable to eat or not. Sushi is a form of Japanese cuisine that makes use of a host of ingredients that might not be commonplace in traditionally Muslim countries.
Fish is perfectly acceptable in Islam, and there is nothing to suggest raw fish is forbidden from being eaten. Most Islamic scripture regarding the safe preparation of meat is concerned with the presence of blood, which is not a concern with fish meat due to their unique circulatory system.
Meat in Sushi
Although not a traditional ingredient in authentic Japanese sushi, many westernized takes on sushi rolls use chicken, duck and beef as ingredients. The manner in which these animals have been slaughtered will determine whether they are considered 'halal' or not. Many restaurants these days cater to halal diets and even prefer sourcing halal meat as they are keen not to lose an important percentage of their customer base. You can easily inquire about the sourcing of the meat used at your local sushi restaurant by either dropping by and asking in person, or obtaining their phone number beforehand and giving them a call to find out. Alternatively you can simply choose to enjoy the huge range of seafood and vegetarian sushi available.
It is not very common to find sushi with pork as an ingredient, but obviously if it did appear on a sushi menu, a Muslim diner would probably not want to order it.
Mirin, sake and rice-wine vinegar
There is some debate about the use of alcohol in cooking and where Islam stands on that. Alcohol content is reduced considerably when brought to a high temperature, and some Muslims argue that by the time Sushi reaches your plate, the amount of alcohol remaining from the creation process is so negligible it cannot be considered haram or forbidden.
On the other hand, some followers of Islam will choose to err on the side of caution and refuse to eat sushi altogether because or the rice-wine vinegar used in treating the rice, and the presence of sake and mirin (another type of sweet rice wine) in various sauces such as Teriyaki sauce.