THE ANIMAL FILES

Giant oarfish

Regalecus glesne

A ribbon-shaped fish can swim upright with its tail pointing down.

Giant oarfish have extremely elongated, silvery bodies and a long dorsal fin with a raised red crest. Deep-water observations show undulating fin movement and vertical orientations. Rare sightings leave many parts of their lives unresolved.[1]

Follow the evidence ↓
Giant oarfish
Image: Sandstein · Commons · CC BY 3.0
Body
Long, ribbonlike and laterally flattened[1]
Movement
Undulating the dorsal fin[1]
Food evidence
Some stomach records contain krill[1]

A fin along the ribbon

The dorsal fin extends along much of the body, with elongated front rays forming the familiar crest. Skin lacks scales, and the mouth has no teeth. A striking silhouette need not imply pursuit of large prey; feeding records include small crustaceans. Many examined stomachs have been empty, limiting conclusions about the full diet.[1]

A fish filmed standing in the water

An ROV filmed a reliably identified individual in the Gulf of Mexico in a head-up, tail-down orientation. Dorsal-fin undulation permits movement. Other footage, attributed more tentatively to this species, also shows horizontal positions; vertical swimming should not be treated as its only possible posture.[1]

Uncertainty is part of the biology

Early stages have been identified using features and DNA barcoding, but observations remain scarce. Long historical size estimates are poorly supported compared with measured specimens. A stranded ribbon-shaped fish may provide anatomy, while underwater footage provides behaviour; neither alone supplies a complete account of breeding or feeding.[1]

A COMMON MIX-UP

Does vertical footage mean the fish can never swim horizontally?

No. Horizontal and vertical positions occur in footage attributed to this species, although not every filmed identification is equally certain.[1]

TRY A LITTLE REASONING

Why is a filmed living fish different evidence from a stranded specimen?

Reveal the explanation

Footage records posture and movement in context; a specimen provides anatomical inspection but not its undisturbed behaviour.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Regalecus glesne (adapted and translated; exact revision)
  2. NCBI Taxonomy — Regalecus glesne (identity and game lineage)

Last fact check:

One discovery leads to another

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