Elusive and alien-looking, the oarfish has a thin, eel-like body with squiggly iridescent markings that glow blue in the video. It also has a long dorsal fin that stretches the length of nearly half its body, and large round eyes rimmed in silver.
That bright white blob you see in the fish's spiny dorsal fins is a parasitic isopod -- sort of like an ocean version of the roly poly bug -- that has attached itself to the fish. It is a common parasite of marine fish, but it is the first time one has been seen on an oarfish, said Mark Benfield, a marine biologist at Louisiana State University.
Benfield is the lead author of a paper describing the oarfish video, published in a recent issue of the Journal of Fish Biology.
Despite its great size, the fish orients itself vertically, with its head toward the ocean surface, and its blunt tail hanging down. This allows the fish to scan the water above for the krill and other small crustaceans that it eats, and may help it appear smaller to predators who are lurking below, said Benfield.