What is "crestfish"

Crestfishes, family Lophotidae, are lampriform fishes found in most oceans. It consists of two extant and one or two extinct genera.

They are elongated, ribbon-like fishes, silver in color, found in deep tropical and subtropical waters worldwide. Their scientific name is from Greek lophos meaning "crest" and refer to the crest (part of the dorsal fin) that emerges from the snout and head; this structure gives them their other name of unicorn fishes.

The extant genera all possess ink sacs that open into their cloacae from which they can produce a cloud of black ink when threatened (as in many cephalopods).