I. Biological Description
Ahi refers to two species, bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares). In Hawaii, shibi is another name for yellowfin tuna. The yellowfin gains its name because the soft dorsal and anal fins and finlets are bright yellow in color. The dorsal and anal fins lengthen with age. Yellowfin range from the ocean surface to depths below 100 fathoms.
II. Of Special Interest For Buying/Distributing
Availability And Seasonality: Caught year-round in Hawaii's waters, yellowfin tuna is usually most abundant during the summer season (May-September). There are wide fluctuations in the annual catch of yellowfin, depending on whether ocean surface temperatures and other oceanographic conditions favor the migration of ahi schools to within fishing range of the Hawaiian Islands.
Fishing Methods: Yellowfin tuna is landed in Hawaii by commercial and sport fishermen. A large part of the commercial catch is harvested by longline boats, which may search for tuna concentrations up to 800 nautical miles from port and set hooks in deep waters. Landings by the handline (ika-shibi) fleet, based largely on the island of Hawaii, are impressive during some years. Trollers contribute the remainder of the commercial catch of yellowfin, as well as all of the recreational catch. Trophy-sized yellowfin tuna are prized catches in gamefishing tournaments held in Hawaii.
Distribution: The longline catch and some of the handline (ika-shibi) catch of ahi is marketed through the Honolulu fish auction. The majority of the handline catch is sold through the fish auction in Hilo and through intermediary buyers on the island of Hawaii. The troll catch may be marketed through fish auctions, intermediaries on all islands, or directly to stores and restaurants, or it may be shared with family and friends.
Most ahi is sold fresh, but surpluses caught during the peak summer season are sometimes dried and smoked.
Substitution: Yellowfin and bigeye tuna are completely interchangeable for sashimi and other raw fish preparations. Yellowfin is also interchangeable with other tunas and with a`u for grilling. Yellowfin is processed, interchangeably with ahi and a`u, into smoked and dried products.
III. Of Special Interest For Preparation/Quality Control
Shelf Life And Quality Control: Yellowfin is more perishable than either bigeye or albacore tuna (see Table 3). Although the yellowfin's flesh tends to be firmer than that of bigeye tuna, it does not retain the natural red pigmentation as long. The quality of yellowfin caught off Hawaii varies considerably with fishing method, care in handling and other factors.
Seasonal, cyclical changes in flesh characteristics occur in many fish species, but they are very noticeable in mature yellowfin tuna landed in Hawaii. Yellowfin caught near the ocean surface during the summer season frequently have some portion of flesh that lacks the typical bright red pigmentation and is more watery and softer than normal ahi flesh. Fish in this condition are often referred to as "burnt" tuna. The condition may be related to spawning, to overheating as a result of frenzied activity on handlines and trolling lines or to handling techniques by small-boat fishermen after capture.
Burnt flesh reduces the value of a fish in the sashimi market. Except in extreme cases, however, burnt tuna can be cooked without tasting the effects of this condition. This has led many fish buyers to recognize only two grades of yellowfin tuna -- sashimi-grade and other -- without differentiating between normal and burnt tuna flesh for the purposes of grilling. In fact, there are considerable differences between normal and burnt flesh in terms of fat content and nutritional value. Up-scale restaurants which recognize the differences between normal and burnt yellowfin flesh say that burnt flesh is more likely to dry out on the grill.
Product Forms And Yields: Yellowfin tuna landed in Hawaii range from 3 to over 200 pounds in size. The smallest fish are usually caught around fish aggregation buoys, whereas the largest are often caught by handline. Longlining harvests a wide range of fish sizes, from 20 to 200 pounds or more. The larger yellowfin (over 100 pounds in round weight) are preferred for several reasons: (1) greater yield of finished products - up to 65% (see Table 5); (2) redder flesh pigmentation (if not "burnt"); and, (3) greater fat content than smaller ahi.
Fresh yellowfin is sold already prepared as sashimi, poke (bite-sized pieces of raw fish seasoned with spices and condiments), or smoked strips. It is also marketed as loins, loin sections, or steaks at fish markets or markets with fish counter service or self-service counters. Small ahi may be sold in the round to retail consumers who prepare their own raw fish dishes or smoked fish.
Large quantities of fresh yellowfin are exported, mostly as dressed (headed and gutted) or loined products, from Hawaii to U.S. mainland.
IV. Of Special Interest To Consumers/Foodservice Personnel
Color, Taste, Texture: Yellowfin tuna has flesh coloration that varies from pink in smaller fish to deeper red in larger fish. Larger fish typically have a higher fat content than smaller fish, and this is a desirable attribute for raw fish products, as well as for broiling.
Fresh yellowfin undergoes oxidation of pigmented protein when exposed to air, so exposed flesh changes from a red to a brown color in a matter of days. For this reason, yellowfin is usually not loined or filleted until shortly before use.
Preparations: Yellowfin tuna is widely used as raw fish dishes, especially sashimi. This fish is also excellent for grilling and has become very popular in "blackened" fish preparations featured in Cajun cuisine. With its mild flavor and firm texture, yellowfin adapts well to numerous applications.
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