Black swallower

Black swallower
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Chiasmodontidae
Genus:	Chiasmodon
Species:	C. niger
Binomial name
Chiasmodon niger Johnson, 1864
Synonyms
Ponerodon vastator Alcock, 1890

The black swallower, Chiasmodon niger, is a species of deep sea fish in the family Chiasmodontidae, notable for its ability to swallow fish larger than itself (for which it is sometimes named the "great swallower").

It has a worldwide distribution in tropical and subtropical waters, in the mesopelagic and bathypelagic zones at a depth of 700-2,745 meters (2,300-9,000 ft).^[1]

Description

This is a small fish, with a maximum known length of 25 cm (10 in).^[1] The body is elongated and compressed, without scales, and is a uniform brownish black in color. The head is long, with a blunt snout, moderately sized eyes, and a large mouth. The lower jaw protrudes past the upper; both jaws are lined with a single row of sharp, depressible teeth, which interlock when the mouth is closed. The first three teeth in each jaw are enlarged into canines.

There is a small lower spine on the preoperculum. The pectoral fins are long, with 12-15 (usually 13) rays; the pelvic fins are small and contain 5 rays. There are two dorsal fins; the first is spiny with 10-12 spines, and the second is longer with 1 spine and 26-29 soft rays. The anal fin contains 1 spine and 26-29 soft rays. The caudal fin is forked with 9 rays. The lateral line is continuous with 2 pores per body segment.^[2][3]

Feeding

The black swallower feeds on bony fishes, which are swallowed whole. With its greatly distensible stomach, it is capable of swallowing prey over twice its length and ten times its mass.^[4] Its upper jaws are articulated with the skull at the front via the suspensorium, which allows the jaws to swing down and encompass objects larger than the swallower's head. Theodore Gill speculated that the swallower seizes prey fishes by the tail, and then "walks" its jaws over the prey until it is fully coiled inside the stomach.

Black swallowers have been found that had swallowed fish so large that they could not be digested before decomposition set in, and the resulting release of gases forced the swallower to the ocean surface. This is, in fact, how most known specimens came to be collected.^[4][5] In 2007, a black swallower measuring 19 cm (7.4 in) long was found dead off Grand Cayman. The stomach of the swallower contained a snake mackerel (Gempylus serpens) 86 cm (34 in) long, or four times its length. It is unclear how the swallower managed to avoid being eaten by the larger snake mackerel, itself an aggressive predator.^[6]

Reproduction

Reproduction is oviparous; the eggs are pelagic and measure 1.1-1.3 mm (0.04-0.05 in) in diameter and contain a clear oil globule and six dark pigment patches, which become distributed along the newly hatched larva from in front of the eyes to the tip of the notochord. These patches eventually disappear and the body darkens overall to black. The eggs are mostly found in winter off South Africa; juveniles have been found from April to August off Bermuda.

The larvae and juveniles are covered in small projecting spinules.^[7][8]

References

1. ^ ^{a b} Froese, Rainer, and Daniel Pauly, eds. (2009). "Chiasmodon niger" in FishBase. March 2009 version.
2. ^ Jordan, D.S. and Gilbert, C.H. (1883). Synopsis of the Fishes of North America. Government Printing Office. 
3. ^ McEachran, J.D. and Fechhelm, J.D. (2005). Fishes of the Gulf of Mexico: Scorpaeniformes to Tetraodontiformes. University of Texas Press. ISBN 0292706340. 
4. ^ ^{a b} Jordan, D.S. (1905). A Guide to the Study of Fishes. H. Holt and Company. 
5. ^ Bullen, F.T. (1904). Denizens of the Deep. F. H. Revell Company. 
6. ^ Boxall, S. (Oct. 9, 2007). "Small fish takes big bite". CaymanianCompass. Cayman Free Press, Ltd.
7. ^ Connell, A. Chiasmodontidae: L II AS. Marine fish eggs and larvae from the east coast of South Africa. Retrieved on March 11, 2009.
8. ^ Richards, W.J. (2006). Early stages of Atlantic fishes: an identification guide for the western central North Atlantic. CRC Press. ISBN 0849319161.