Overview
The Smalleye Pacific Opah (Lampris incognitus) is a magnificent, disk-shaped pelagic marine fish belonging to the family Lampridae. Formally described through comprehensive genetic revisions of the cosmopolitan ‘moonfish’ complex, this remarkable deep-water giant inhabits the vast open expanses of the Pacific Ocean. Renowned among marine biologists for its endothermic capabilities—possessing internal countercurrent heat exchange networks that make it functionally warm-blooded—it maintains elevated cranial and muscle temperatures while cruising cold mesopelagic depths.
Biology and Physical Characteristics
Lampris incognitus possesses an impressive, laterally compressed oval silhouette that gleams with iridescent steely-blue and rose-pink hues, profusely stippled with silvery-white spots. Its fins—including elongated falcate pectoral fins and a sweeping dorsal fin—are bright vermilion red. Internally, it features a specialized network of countercurrent blood vessels (retia mirabilia) embedded in its gill arches and pectoral musculature. These retia insulate warm metabolic blood generated by rapid pectoral swimming, keeping its eyes, brain, and heart up to 5°C warmer than ambient sea temperatures.
Behavior and Ecology
Unlike sluggish deep-water ambushers, the smalleye Pacific opah is an agile, active predator that flies through the water column by flapping its powerful red pectoral fins in a continuous sculling motion. Traveling between 50 and 400 meters depth, its warm eyes and enhanced brain processing allow it to spot fast-moving mesopelagic squids (such as Onychoteuthis and Histioteuthis) in near darkness, lunging with explosive speed to inhale prey through its toothless, highly protrusible jaws.
Conservation and Human Impact
The IUCN evaluates Lampris incognitus as Least Concern. Because opahs lead solitary lives in deep offshore open-ocean waters, they are rarely targeted directly by commercial fleets. However, they are frequently captured as prized incidental bycatch in pelagic longline fisheries pursuing bigeye tuna and swordfish in Hawaii and the eastern Pacific. Their dense, fatty meat—valued for its high oil content and diverse culinary textures—commands high prices in international seafood markets, warranting continued fishery monitoring.
Interesting Factoid
The Smalleye Pacific Opah is one of the only fully warm-blooded fish in the entire ocean: while almost all other fish take on the freezing temperature of deep water, the opah flaps its big red wings non-stop to keep its heart, brain, and eyes toasty warm like a bird!
Last updated: October 2026