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Black swallower

Black swallower

Deep-sea fish that eats prey larger than itself

Photo: Unknown author, Public domain, via Wikimedia Commons

The black swallower is a small deep-ocean fish found in tropical and subtropical waters worldwide. It is famous for swallowing bony fish and cephalopods much larger than its own body using a highly expandable stomach.

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  • Swallows prey up to 10 times its own mass
  • Found at depths between 700 and 2,745 metres
  • Teeth are loose in sockets to help chew prey
  • Most specimens found dead after floating to surface

What it is

This species is a small, scaleless fish with an elongated and compressed body. It appears uniform brownish-black in colour. The head features a blunt snout, moderate eyes, and a large mouth where the lower jaw extends beyond the upper. Both jaws hold a single row of sharp teeth that can depress and interlock. The first three teeth on each side are enlarged into canines. Two dorsal fins sit on its back, along with small pelvic fins and long pectoral fins. A continuous lateral line runs along its sides.

Where it lives

It inhabits tropical and subtropical waters across the globe. This fish lives in the deep ocean, specifically within the mesopelagic and bathypelagic zones. Its typical depth range spans from 700 to 2,745 metres. It is a widespread and common organism in these dark waters. Within its genus, it is the most frequently encountered species in the North Atlantic region.

How it lives

The diet consists mainly of bony fish and cephalopods. It captures these animals and swallows them entirely. The stomach is highly distensible, allowing it to ingest prey more than twice its length and ten times its mass. The upper jaws connect to the skull in a way that lets them swing down to encompass large objects. It may seize prey by the tail and work its jaws over the body until the meal is coiled inside.

Breeding and life cycle

Reproduction occurs through egg-laying. The eggs are pelagic, meaning they float in the open water column. Each egg measures about 1.1 to 1.3 mm in diameter and holds a clear oil globule. Six dark pigment patches are visible inside, which later distribute along the larva's body. These markings fade as the young fish matures and turns black. Eggs are often found in winter off South Africa, while juveniles appear near Bermuda in spring and summer.

Black swallower
A drawing made by EveryFish from what this page says. It is a diagram, not a picture of the real fish.

Fish and people

Most known specimens were collected after dying and floating to the surface. This happens when gases from decomposing prey build up in the stomach. In 2007, a dead specimen off Grand Cayman contained a snake mackerel four and a half times its own length. Such events provide researchers with rare opportunities to study the feeding habits of this deep-sea creature.

A specimen of the black swallower Chiasmodon niger, caught in the NE Atlantic. The large mouth and sharp teeth are visible, as is the dark skin (though this is damaged in some places). Note: the stomach is distended, how
A specimen of the black swallower Chiasmodon niger, caught in the NE Atlantic. The large mouth and sharp teeth are visib. Photo: HulloThere, CC0, via Wikimedia Commons
Black Swallower (after having swallowed a large fish)
Black Swallower (after having swallowed a large fish). Photo: G.H.Ford (1809-1876), Public domain, via Wikimedia Commons

Questions people ask about Black swallower

How big does the black swallower get?

It is a small fish that averages between 15 and 20 cm in length. The maximum recorded size for this species is 25 cm.

What does the black swallower eat?

It feeds on bony fish and cephalopods. It swallows these prey items whole, often choosing animals much larger than its own body size.

Why do they float to the surface?

If prey is too large to digest quickly, it decomposes in the stomach. The resulting gas buildup forces the fish to float up, where it often dies.

Good reading and sources

Where this page comes from

The facts on this page come from the Wikipedia article "Black swallower", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.

It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.

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Photo credits on this page

The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.

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