Ahi is a form of tuna derived from either the yellowfin or bigeye tuna. It is frequently caught in warm Pacific waters and sold fresh. It is found in great numbers in both Hawaii and off the Pacific Coast of Mexico and Southern California.
This type of tuna is tremendously popular in sashimi, which is sushi containing raw fish. However, some ahi may not be good enough quality for sashimi, because especially the yellowfin can swim close to the surface of the water, causing the skin to burn. The resulting “burned” fish remains acceptable for cooked dishes, but most sushi chefs will reject it for use in sashimi.
Yellowfin ahi is particularly popular in sport fishing because the fish can be relatively large. They are sometimes also called cow tuna, but that is a bit of an exaggeration. There are, however, records of some ahi weighing over 200 pounds (90.71 kg). Bigeye tuna can also weigh up to 200 pounds, though average weight tends to be around 20 pounds (9.07 kg).
The flesh of ahi ranges from pink to deep red. Larger fish tend to have a deeper color. Larger fish also are higher in fat, which from a gourmet standpoint is preferable. In addition to its use for sashimi, many enjoy grilling or poaching the loin or fillets. Usually, 50% of a medium sized fish will yield fillet cuts.
Bigeye tuna as a source of ahi is generally preferable if the tuna must be shipped. It has a slightly longer shelf life than yellowfin tuna, so stays fresher longer. If one doesn’t live in an area where the fish frequents, many companies can ship the fish overnight, so it still remains fresh.
Bigeye tuna is a little less available than yellowfin, because bigeyes tend to swim very deep, often evading even the most practiced commercial fisherman. Both types of ahi tend to be fished in specific seasons and are most prevalent in October through April. Highly commercialized fishing has led to more catches of both types out of season, and these fish are still considered excellent for consumption.
Though most fish were once considered to be the best of health foods, scientists have become increasingly concerned about high levels of mercury contained in fish like ahi. Most health experts now recommend consuming fish no more than once weekly, and recommend even less for children and for pregnant women, as they are the most susceptible to mercury poisoning.