Q: I always assumed that the baitfish we catch are thread herring. But I looked through a copy of the venerable Atlantic Coast Fishes from Peterson Field Guides, and it shows thread herring having tails with no spotting of any sort. Yet, as this image clearly shows, this common baitfish has black tips on its tail fin. In fact, none of the herring shown in the Peterson Guide have black tips on the tail. So I'm wondering just what we're catching down here?

Freddy Figleheimer
Miami, Florida

A: From what I can see in your photograph, you're catching Atlantic thread herring, Opisthonema oglinum, also called threadfin herring, greenies or greenback herring. A field guide can't possibly show or describe all color variations that can occur in a species. I checked the description of O. oglinum in a much more detailed publication, Fishes of the Western North Atlantic, published by the Sears Foundation for Marine Research, Yale University. The section on O. oglinum, written by the late, noted ichthyologist Samuel F. Hildebrand states, "Back bluish-green in life, the rest of body silvery. A dark shoulder spot usually present. Rows of scales on back with more or less definite dark lines. Fins chiefly translucent, the dorsal and caudal lobes generally with dark tips." The illustration that accompanies Hildebrand's description also depicts an individual with distinctly pigmented tips on its dorsal and caudal fins. However, as one can tell from Hildebrand's description, not all Atlantic thread herring have dark shoulder spots and/or dark dorsal and anal fin tips. Thus, while your fish is a typical example of O. oglinum, the fish illustrated in Atlantic Coast Fishes appears to be a bit atypical, although its pigmentation is still well within the range of variation reported for this species. — Ray Waldner