Mahi mahi, also called dolphinfish, is one of the fish that's lower in mercury, so even pregnant women can safely consume up to six 6-ounce servings per month. The calories in mahi mahi are comparable to those in halibut, haddock, flounder and cod; it has fewer calories than salmon, mackerel and tuna. Mahi mahi is also lower in heart-healthy omega-3 fats than these fish, with only 118 milligrams per 3-ounce serving.

A 3-ounce serving of mahi mahi has 93 calories, almost all of which come from the 20.2 grams of protein it contains. Mahi mahi isn't a significant source of carbohydrates, and it contains only 0.8 grams of fat per serving. If you use oil to grill your mahi mahi, this will increase the fat and calorie content. For example, a teaspoon of olive oil contains 40 calories and 4.5 grams of fat.