Which Tuna is Which?

Biologists regard the tunas as members of the mackerel family. To a big tuna this must sound like a demotion, if not a downright insult.

We all know that mackerels are mostly long and skinny while tunas are fat and sometimes huge. Science, nevertheless, insists on referring to the whole bunch as mackerels.

The main feature common to both sub-groups is a row of finlets running between the dorsal fin and the tail, and a similar row on the underside. No other kinds of fish sport those finlets, and so it’s obvious that the mackerels and tunas are close relatives. But wouldn’t “finlet fishes” be a better label for this widely individualistic family than “mackerels?” Just asking.

Anyway, the finlets do help with identification, because the common names of “blackfin” and “yellowfin” derive from the color of those finlets, and not from the color of the more prominent fins. For some reason, though, this naming system did not extend to the bluefin tuna, whose finlets are yellow.

Because not every species of tuna has its own finlet color, other clues to identity must be sought. Following is a list of the Florida/Bahamas tunas with their main identifying features.

ALBACORE—Although rare in local waters, this one is easy to spot by its very long pectoral fins, which extend past both the dorsal and anal fins.

BIGEYE TUNA—Because it stays very deep nearly all the time, this tuna is not often seen. Although the finlet color—yellowish with dark edges—is much the same as that of the yellowfin, the bigeye is distinguishable by its short dorsal and anal fins. Yes, the eye is indeed bigger, but not so much that you’re likely to tell the difference without a side-by-side comparison. The bigeye can be the most difficult of all our tunas to identify. Even biologists sometimes need to examine the liver to make sure.

BLACKFIN TUNA—Its relatively small size and gold or brassy tones make it easy to distinguish. Confusion with a small specimen of yellowfin tuna is possible, but here the finlets ride to the rescue. Those of the blackfin are, well, black, and of the yellowfin, yellow.

BLUEFIN TUNA—Giant bluefins need no identifying marks, but, occasionally, some juvenile schoolies show up off Florida. Their finlets are yellow with dark edges as on the yellowfin, but the overall color of the bluefin is dull blue or dark gray, and the fins are shorter.

BONITO, ATLANTIC—This small fish has longitudinal stripes above the lateral line.

LITLE TUNNY (Florida Bonito)—The only “bonito” with spots, it is also marked with a wavy pattern on the upper rear sides.

SKIPJACK TUNA (Oceanic Bonito)—On this fellow, the longitudinal stripes are found below the lateral line.

YELLOWFIN TUNA—Very long streamers trailing from the dorsal and anal fins identify many larger specimens. With fish small enough to be confused with large blackfin tuna, look for a vague vertical pattern on the sides, with a gold or silvery sheen on the lower sides and underside. If still not sure, fall back to finlet color.

FS