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October 26, 2001

Butterfly Tuna

This New Zealand fish is actually a mackeral.

Q: I saw this dark, large-scaled fish, more than 5 feet long, being unloaded from a longliner in Tauranga, New Zealand. They called it a "butterfly fish," but it looks like a cross between a bluefish and a tuna to me. Can you tell me anything about this fish? - David Gong, San Francisco, California

A: It's a butterfly mackerel (Gasterochisma melampus) - sometimes called butterfly tuna, butterfly kingfish or scaly tuna - an oceanic species occasionally caught by longliners or found washed ashore in New Zealand and southeastern Australia. It's easily distinguished from other mackerels and tunas by its large scales. Young butterfly mackerel have an unusual, extremely large ventral fin extending down from the "neck" of the fish like a long scarf, which can be folded into a groove along the fish's belly when it swims. The ventral fin decreases in size as the fish gets older. The butterfly mackerel is a deepwater fish growing to about 6 feet long, but little is known of its life history.