Butterfish look unremarkable, a small, round, silvery disc of a fish, but any tuna angler will tell you they are one of the most consequential baits in the ocean. When bluefin tuna key on a thick body of butterfish, they can become almost impossible to catch on anything but the real thing, a phenomenon known as the butterfish bite.
What they are
Butterfish are deep-bodied, round and thin, bright silver, and small, a perfect, easy mouthful. They school in open water and over structure, sometimes in huge concentrations, and a wide range of predators eat them, but their outsized reputation comes from their effect on bluefin.
The butterfish bite
When there is an enormous amount of butterfish in the water, tuna feed lazily and selectively, sipping the naturals and refusing lures, bars and anything that stands out. This is the classic match-the-hatch problem on a grand scale, and the solution is a real butterfish drifted naturally on a light leader. The technique has its own page: see bluefin on butterfish.
Tip If you are marking tuna that will not eat a thing, check what is in the water. A boat surrounded by butterfish means it is time to stop throwing hardware and match the hatch with the real bait, drifted drag-free.
How anglers use them
Butterfish are fished as dead or live bait, dead-drifted in a slick or on a light leader, and they are also a common chunk and slick bait for chunking. When fish are keyed on them, presentation and a light leader matter more than anything.