Lean fish have significantly less fat than other protein-rich foods, and the fattier fish have a fat content similar to lean meats. To get a good general idea of the fat content of most fish species, look at the color of the flesh. The leanest species such as cod and flounder have a white or lighter color and the fattier fish such as salmon, herring, and mackerel will have a much darker color. The fat content of fish and shellfish can vary considerably over time. Fat levels are also influenced by the type of food that is eaten, so fish of one species may have either more or less fat than the same species taken from another location.
Fat levels tend to be lower during spawning or reproduction, and when food is less plentiful.
The following table groups a selected variety of fish and shellfish according to their average amount of total fat and percent calories from fat to assist in comparing common seafood choices. When evaluating a food it's important to consider both the total amount of fat and the kind of fat that it contains. Monounsaturated and polyunsaturated fats are two types of unsaturated fat. Current dietary recommendations suggest that we decrease the amount of saturated fat that we consume to less than 10 percent of our total calories, and that we increase the proportion of fat that is unsaturated in our diet. For most seafoods, less than 10 percent of the total calories are from saturated fat.