Hawaii Seafood Buyers' Guide - Species Descriptions: Tuna

Aku - (Skipjack Tuna)

Aku (Katsuwonus pelamis)
Skipjack Tuna
French: Bonite A Ventre Raye
German: Echter Bonito
Italian: Tonnetto Striato
Spanish: Listado, Barrilete
Japanese: Katsuo
Hawaii names: Aku

I. Biological Description
Aku (Katsuwonus pelamis) is commonly known as skipjack tuna. Other names for this species include striped tuna, oceanic skipjack and katsuo. This near-surface schooling tuna is widely distributed across the Pacific Ocean.

II. Of Special Interest For Buying/Distributing

Availability and Seasonality: Aku is historically the most important single commercial fish species in terms of landed weight and value in Hawaii, as well as throughout much of the central and western Pacific. Hawaii's aku fishery, however, is characterized by wide annual and seasonal fluctuations in landings. Aku caught in Hawaii routinely range between 4 and 15 pounds in round weight, but larger fish (16 to 30 pounds in round weight), move into Hawaiian waters during the summer season of increased abundance (April-September).

Fishing Methods: Most of the aku catch in Hawaii is landed by commercial pole-and-line fishermen who induce aku to bite on feathered hooks by chumming with live bait. The pole-and-line catch is sorted according to fish size and is initially stored and sold in tubs head down so that blood drains away from the flesh. Trollers and longline boats land the remainder of the aku catch.

Distribution: Troll-caught aku is marketed through fish auctions in Honolulu and Hilo, through intermediary buyers on all islands, and by peddlers from the roadside. The pole-and-line aku, fleet, which is centered on the island of Oahu, markets its catch through intermediaries who sell to fresh fish outlets.

Substitution: Although ahi are often the preferred species for sashimi, aku can be substituted and, in fact, is preferred by some. When cooked, the red-fleshed aku lightens considerably in color, so it is interchangeable with ahi and a`u in broiled or fried forms. Aku, ahi, and a`u are also interchangeable for dried and smoked products, but due to their larger size, ahi and a`u offer better yields.

III. Of Special Interest For Preparation/Quality Control

Shelf Life And Quality Control: Even with the best care, aku has a relatively short shelf life as a high quality product and is generally consumed within 6-7 days after landing (See Table 3). Aku which has been caught by trolling or pole-and-line is fresher and, hence, has a longer shelf life than that caught by longline boats, which make longer fishing trips.

Aku keeps longer if it is stored whole (especially if head down) and is not filleted until shortly before use. Larger summer fish (16-30 pounds in round weight) keep better than smaller fish. The first evidence of deterioration is a transformation of the deep red color of the meat to a brownish-red or rainbow color, accompanied by loss of firm texture.

It is not uncommon to find small worms in the belly flaps of aku. Studies have shown that these parasites present little, if any, health hazard, and they can be easily removed or destroyed by cooking.

Product Forms And Yields: Aku is sold in various forms: whole fish, fillets, steaks, in raw fish preparations or as dried fish sticks. Much of the aku catch is sold fresh, but surpluses caught during the peak summer season are sometimes processed. Some of the excess summer fish are dried. The yield of fillet from whole fish varies from 45% for small aku to 60% for large aku (see Table 5).

Filleting Aku: Remove the dorsal fin, head, gills and guts. Cut into the fish from both sides to establish slits along the backbone. Join these slits at the narrowest part of the fish (the tail) and fillet along the bone all the way to the collar.

IV. Of Special Interest To Consumers/Foodservice Personnel

Color, Taste, Texture: Good quality aku has firm flesh that is deep red in color. Flesh color varies with the size of the fish, with smaller fish having a lighter red color than larger fish; hence, larger aku are preferable for raw fish preparations requiring a red flesh. Larger aku have a greater fat content than smaller aku and this is another desirable attribute for raw fish dishes. Cooking causes the flesh to become lighter in color.

Aku has a more pronounced taste than ahi or a`u. This is an advantage in satisfying local ethnic taste preferences, but it may not be as desirable in other markets.

Preparations: Aku is the preferred species for many ethnic seafood dishes, especially poke, raw fish served in bite-sized pieces with various spices and condiments. Many Japanese and Hawaiian consumers prefer sashimi prepared from large aku to that from ahi. "Aku bone" (the backbone of a filleted fish which retains thin strips of flesh) is a favorite food among certain ethnic groups in Hawaii, as are aku roe and dried aku.

Aku can be cooked in many different ways, but is usually broiled over hot coals, sauted or fried in a skillet. The meat cooks quickly and can easily dry out if overcooked.

V. Historical Note

Aku figures prominently in Hawaiian legends. According to one legend, while voyaging to settle in Hawaii from the south seas, a chief and his party were caught in a storm which threatened to swamp their canoes. In response to the prayers of the sailors, a school of aku appeared and calmed the rough waters. To honor this fish, it was forbidden for Hawaiians to eat aku for a few days each year.

Ahi - Bigeye

Ahi, Bigeye (Thunnus obesus)
Bigeye Tuna
French: Thon Obese
German: Grossaugenthun
Italian: Tonno Obeso
Spanish: Patudo
Japanese: Mebachi
Hawaii names: `Ahi po`o nui; `Ahi

I. Biological Description

Bigeye tuna (Thunnus obesus) is one of two species known in Hawaii simply as ahi. Similar in general appearance to yellowfin tuna (the other species known as ahi), the bigeye may be recognized by its plump body, its larger head and its unusually large eyes.

Adult bigeye tuna are the deepest occurring of all tuna species, with the depth range of greatest concentration at 150 to 250 fathoms. Smaller bigeye (20-30 pounds) may be encountered in shallower waters in the vicinity of seamounts or floating objects, including fish aggregation buoys.

II. Of Special Interest For Buying/Distributing

Availability And Seasonality: The availability of bigeye tuna in Hawaii has increased as a result of an expansion of the domestic longline fleet and an extension of the fleet's fishing range to as far as 800 nautical miles from port.

The peak in Hawaii's landings of bigeye tuna occurs during the winter season (October-April), which is the off-season for harvesting other tuna species.

Fishing Methods: Bigeye tuna is harvested in Hawaii primarily by longline boats which set hooks at the deep swimming depths of this species. Bigeye tuna is a minor component of the catch made by the small-boat handline (ika-shibi) fleet off the island of Hawaii. It is rarely caught by trollers.

Distribution: The longline catch of bigeye tuna is marketed primarily through the Honolulu fish auction. Most of the handline (ika-shibi) catch is sold through the fish auction in Hilo and through the intermediary buyers on the island of Hawaii. Virtually all bigeye is sold fresh.

Substitution: Caught in deeper, cooler water, bigeye tuna typically has a higher fat content than yellowfin and is preferred over yellowfin by more discriminating sashimi buyers. For less discriminating raw fish consumers, the two species are interchangeable. They are also interchangeable with other tuna and marlin species for grilling purposes.

III. Of Special Interest For Preparation/Quality Control

Shelf Life And Quality Control: Bigeye tuna has a longer shelf life than yellowfin tuna, and the natural red flesh is slower to discolor after exposure to air. Longline-caught bigeye rarely develop the "burnt" flesh problems often found in yellowfin taken on handline and trolling gear.

Some longline boats which catch bigeye tuna remain at sea for up to 10-12 days, but with proper care, the fish will retain a high quality for over two weeks after capture (see Table 3). Although not as old when landed, the quality of handline-caught bigeye is more variable due to differences in handling by small-boat fishermen.

In bigeye which have been stored too long after harvest, the entrails burst, releasing stomach acids and bile into the gut cavity. The gut cavity is stained greenish-yellow as the acids attack the stomach wall and eventually cause the flesh to deteriorate.

Product Forms And Yields: Bigeye tuna landed in Hawaii range from 20 to over 200 pounds in round weight. The smallest fish are usually caught around fish aggregation buoys and over seamount summits, whereas the largest are usually caught in deep open ocean waters. The larger fish are preferred for their typically higher fat content and greater yields. These fish often enter the sashimi market. Smaller fish of good quality may also be used for sashimi, but there is a growing demand for fresh bigeye in the 20-50 pound size range for grilling in up-scale restaurants on the U.S. mainland.

Fresh bigeye may be sold already prepared as sashimi, and it is also marketed as loins, loin sections, or steaks at fish markets or markets with fish counter service or self-service counters. It is usually exported in dressed (headed and gutted) form or as loins. The yield of fillet from a whole ahi varies from 55-65%, depending on fish size (see Table 5).

Quartering Ahi: Remove the ahi's head by sawing beneath the gill plate and through the bone. Next, with the tip of a sharp knife, cut through the thin layers of intermuscular bone laterally connected to the spine. Once these bones have been severed, a clean fillet can be made without tearing the flesh. Fillet cuts should be made as close to the bone as possible.

IV. Of Special Interest To Consumers/Foodservice Personnel

Color, Taste, Texture: Bigeye tuna of good quality has reddish-pinkish flesh color. When exposed to air, bigeye tuna flesh will begin to discolor (although at a rate slower than yellowfin flesh). For this reason, bigeye is usually not loined or filleted until shortly before use.

Larger bigeye typically have a higher fat content than smaller bigeye, but even a fish as small as 25-30 pounds may be rich in fat.

Preparations: Bigeye tuna is one of the preferred species for the preparation for sashimi. With a high fat content, bigeye is also among the most desirable species for grilling. Its mild flavor adapts well to numerous applications.

Tombo

Tombo (Thunnus alalunga)
Albacore Tuna
French: Germon
German: Weisser Thun
Italian: Tonno Bianco, Alalonga
Spanish: Albacora, Atun Blanco
Japanese: Bincho; Binnaga; Tombo
Hawaii names: `Ahipalaha

I. Biological Description

Tombo ahi (Thunnus alalunga) is commonly known as albacore tuna. Other names for this species include Pacific albacore, tombo, and "white meat" tuna. The tombo ahi caught in the vicinity of the Hawaiian Islands are large (over 40 pounds in round weight) adult fish. Smaller, immature tombo migrate extensively throughout the North Pacific far north of the Hawaiian Islands.

II. Of Special Interest For Buying/Distributing

Availability And Seasonality: Commercial landings of tombo ahi have increased in Hawaii. Tombo ahi is seasonally available in significant quantities, but is scarce in the off-season. The peak in landings usually occurs from May through September. There are also wide fluctuations in the annual catch of tombo ahi. Availability is greatly influenced by oceanographic conditions. Tombo ahi is believed to migrate along ocean temperature "edges" rich in food, hence, disruption of ocean-wide current systems, such as brought about by "El Nino" weather, may affect catch rates in Hawaii.

Fishing Methods: Most of the tombo ahi catch in Hawaii is landed by commercial longline boats which set hooks at the swimming depths of the large tombo (75-150 fathoms). A small portion of the catch is made by the small-boat handline (ika-shibi) fishery based on the island of Hawaii.

Distribution: The longline catch and much of the handline (ika-shibi) catch of tombo ahi is marketed through the Honolulu fish auction. The remainder of the handline catch is sold through the fish auction in Hilo and through intermediary buyers on that island.

Most of the albacore caught in Hawaiian waters consist of mature fish, 40 to 80 pounds in round weight. Most of this fish is sold fresh, but surpluses caught during the peak summer season are sometimes smoked.

Substitution: Despite having a pinkish rather than reddish flesh, tombo ahi occasionally substitutes for other species of ahi or for aku in raw fish preparations. It is completely interchangeable with other ahi or a`u species in broiled or sauted forms, although it may be more susceptible to overcooking than the other species. Tombo is also interchangeable with other tuna and marlin (a`u) for dried and smoked products.

III. Of Special Interest For Preparation/Quality Control

Shelf Life And Quality Control: Some longline boats which catch tombo ahi are at sea for up to 10-12 days, but with proper care, the fish will retain a high quality for three weeks after capture (see Table 3). Although not as old when landed, the quality of handline-caught tombo is more variable because of differences in handling by the small-boat tuna fleet.

Product Forms And Yields: The preferred market size of tombo ahi for use in fresh or processed products is greater than 50 pounds in the round. The larger fishes have several advantages: (1) greater yield of finished product -- 60-65%, (see Table 5); (2) pinker flesh coloration; and, (3) greater fat content than smaller tombo.

Fresh albacore is also marketed as loins, loin sections, or steaks at fish markets or supermarkets with fish counter service or self-service counters. Tombo is one of the preferred species for gourmet smoked fish products.

IV. Of Special Interest To Consumers/Foodservice Personnel

Color, Taste, Texture: Tombo ahi has flesh that varies from whitish-pink in smaller fish to deep pink in larger fish. Larger tombo ahi have a greater fat content than smaller fish, and this is a desirable attribute for raw fish products, as well as for broiling.

As raw fish, tombo is softer than other ahi or aku and, hence, more difficult to slice into sashimi. The flesh becomes much firmer when cooked than when in the raw state.

Preparations: Restaurants usually grill tombo ahi, but other cooking methods will work as well. Tombo has a tendency to dry out quickly, so it is important to avoid overcooking.

V. Historical Note

Albacore is the only tuna species which can be canned as "white meat" in the U.S. The west coast albacore fishery began in the early 20th century as canning techniques were perfected. However, it was twenty years before albacore became recognized as a premium canned product. With recent cannery closures on the U.S. west coast and wide fluctuations in cannery prices for tombo ahi, an increasing quantity is entering the fresh and fresh frozen restaurant market.

Yellowfin - Ahi

Ahi, Yellowfin (Thunnus albacares)
Yellowfin Tuna
French: Albacore
German: Gelbflossenthun
Italian: Tonno Albacora
Spanish: Rabil
Japanese: Kihada
Hawaii names: `Ahi

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.

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.