Bonito / Tongol Tuna
[Island Skipjack, Black Skipjack, Kawakawa (Hawaii), Tongol Tuna, Little Tuna, Mackerel Tuna (English); Tulingan (Philippine); Tongkol (Malay); Euthynnus affinis]
This small Indo Pacific tuna is found from the east coast of Africa to Hawaii and is an important commercial fish. Unlike the Skipjack proper (Katsuwonus pelamis) it stays fairly close to shore. It can grow to 39 inches and over 30 pounds, but the photo specimen was 19-1/2 inches and 3-1/4 pounds, about typical for Southern California markets. Photo © cg1.
This fish is not currently considered endangered, IUCN Red List status is NE (Not Evaluated). The Monterey Bay Aquarium rates this fish as "Good Alternative" if it comes from Malaysia, or pole / troll caught anywhere, otherwise "Avoid" due to uncontrolled bycatch problems. Now how you're supposed to tell how a frozen bonito in an Asian fish market was caught, I haven't a clue.
More on Varieties of Fish (very large
Some sports fishermen say Bonito tastes like a "grilled football", and others say it's delicious. Clearly the difference is in how it's cooked. Bonito are very well regarded in regions that know how to cook fish, particularly Japan, Southeast Asia and Spain.
In all prep and cooking matters this fish is practically identical to the deep ocean Bonito / Skipjack (Katsuwonus pelamis). The flesh is dark red, darker than any beef, nor does it want to be served with white wine but rather a substantial red. The flesh is very tender raw but becomes quite firm when cooked. Use where fresh tuna is called for and you don't mind it being dark meat, or use in place of mackerel (it's a bit milder). Commercially this fish is sold canned or frozen, and sometimes dried, salted and smoked.
Buying: This fish is usually available in the Asian markets here in Los Angeles and is quite economical, often selling for US $1.99/pound. If Tongal isn't available Skipjack probably is.
Scales: This fish has a few scales, up at the head end and supposedly by the dorsal fin though I've only found them near the head. Just these few are sufficient to make the fish kosher.
Cleaning: This is a very messy fish to clean - there will be blood, dark blood, and lots of it. Far more blood than you'd ever expect from a fish - have plenty of cold running water to rinse it away. The gill arches hold pretty hard so it's convenient to cut them away at the ends. The innards will need to be cut off at the head end as they don't pull out easily. The gills are very large but soft and cut out fairly easily with kitchen shears.
Fillet: Island Skipjack is not particularly difficult to fillet, except for all that blood. There are bones to follow, but you'll need to cut around the hard surround at the dorsal and anal fins. I first cut off the head - slant your knife strongly under the collar to get as much flesh as possible. When I get to the rib cage I cut the ribs from the backbone with kitchen shears and pull them from the fillet with long nose pliers, they rake back very sharply so need to be pulled out almost straight forward. There are lots of centerline spines that should be pulled, quite long at the very front but getting very short and soft as you work toward the tail. As you do, you'll notice prominent tendons - something you don't see in most fish. They can be left in.
Some instructions say to cut out the "blood line", the darker, stronger tasting flesh along the centerline - but if you do you won't have much fish left. If you don't like the strong flavor, use a different fish.
Skin: The skin has moderate shrink and blisters off the flesh, so it can be left on for pan frying, where it's relatively high oil content and stronger flavor are an asset rather than a liability. For other cooking methods it should be removed. It is relatively thick at the tail end and becomes very thick at the head end. It does not adhere well over most of the fish so it's not hard to remove using the usual long knife and cutting board method. It is soft in the middle so the knife has to be held at as neutral an angle as can be managed without taking off significant flesh. Skin will remain on the skirt, it's thin and adheres very well there.
Yield: A 3 pound 4 ounce fish yielded 1pound 13-3/4 ounces of skin-on fillet (57%) and 1 pound 10-3/8 ounces skin-off (51%). The skirts are small and thin, and the lining membrane shrinks severely and unrelentingly, so I usually cut them off and toss them in the soup pieces bag in the freezer or just fry them up as a small snack.
Stock: The head, fins and bones, after initial ugliness, make a surprisingly clear and very fine soup stock. Bring to a boil in an open pot. As it comes to a boil there will be a lot of ugly reddish brown scum which you should skim off. Simmer for 1/2 hour, then strain and separate the oil using your gravy separator.
Health and Nutrition: There have been reports of ciguatera poisoning in tropical reef regions. Since it's a small tuna it doesn't pose a mercury hazard.