Sashimi is thinly sliced raw meat, usually fish, like salmon or tuna and it is served without rice.
Sushi is not raw fish, but rather vinegared rice mixed with other ingredients as well, which may or may not include raw fish. In some countries, the terms "sashimi" and "sushi" may be used interchangeably, however this is incorrect usage.
How many calories and carbs, or how much fat, fiber, or protein, is in a sashimi or sushi dish depends mostly on the fish or meat used in it. Usually, sushi has more calories and carbs because it uses rice and other ingredients, like mayonnaise for instance, and sashimi does not. Both dishes often use fish, so they tend to be high in omega-3 fatty acids.
Tuna and salmon are two of the most popular fishes used in sashimi, however there are a variety of other kinds of meat and fish used beyond them. Sea bream, mackerel, and yellowtail are common, as are some shellfish and mollusks, such as squid or octopus, shrimp, scallops, and clams. Salmon eggs and sea urchins can also be found. There are different types of sushi, however all contain vinegared rice. Sushi rolls are usually wrapped in dried sheets of seaweed, rice paper, or yuba (soybean skin). Some of the most common types of sushi include nigiri, gunkan (small dried seaweed cups filled with seafood), and temaki (nori seaweed "cones" containing seafood and vegetables).
Within the U.S., the main requirement for fish that is intended to be eaten raw is that it must first be frozen, as this minimizes the risk of foodborne illnesses.
Regardless fish is eaten raw or cooked, mercury and other heavy metal contaminants are a concern, therefore consuming considerable quantities of sashimi or sushi isn’t recommended. Also, women who are pregnant or those who have compromised immune systems are advised to avoid raw fish and to limit the consumption of certain cooked fish, including tuna.