Narcinidae

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Numbfishes
Lesser electric ray, Narcine bancroftii
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Torpediniformes
Family: Narcinidae
Gill, 1862
Genera

Benthobatis
Diplobatis
Discopyge
Narcine

The numbfishes are a group of electric rays (order Torpediniformes) in the family Narcinidae.[1] Some sources include the sleeper rays, family Narkidae, as a subfamily of the Narcinidae.[2] They are bottom-dwelling cartilaginous fishes with large pectoral fin discs and long tails. They can produce an electric discharge for defense, from which their scientific name is derived (Greek narke, meaning "paralysis").[3]

Contents

[edit] Distribution and habitat

Numbfishes are found almost worldwide in warm temperate and tropical continental and continental insular waters. They are strictly marine and are absent from rivers and lakes. They occur in sandy beaches, muddy enclosed bays, estuaries, off coral reefs and river mouths, and on the upper continental slope to a depth of 1,071 meters.[4]

[edit] Description

Small to medium-sized rays, adult numbfishes range from 15 to 66 cm long, though most are less tha 50 cm. They have oval, rounded, or shovel-shaped pectoral discs and stout tails of equal or longer length. The snout is moderately elongated, rounded or rounded-angular, differing from the narkids in being supported by broad rostral cartilages. The mouth is straight, with stout, elongated, and highly protrusible jaws and a prominent groove around its periphery. The nostrils are just forward of the mouth and connected to it by a broad groove; the nasal flaps are short but merged into a broad nasal curtain that overlaps the mouth. The teeth are small have a single moderate cusp; the teeth and tooth bands are exposed when the mouth is closed (except in Diplobatis). There are two prominent dorsal fins of roughly equal size, and a large caudal fin.[4][5]

Numbfishes vary in color from whitish, yellowish, brownish, grey-brown, greenish, reddish, or black above, either plain or with small to large spots, blotches, bars or lines, sometimes forming complex eye-shaped spots or ocelli on the pectoral fins. They are usually white underneath, or black in deep-water species. The large, kidney-shaped electric organs are at the base of the pectoral fins and visible through the skin.[4]

[edit] Biology and ecology

Numbfishes are slow-swimming bottom-dwellers that feed on small fishes and invertebrates off the bottom; their protrusible jaws aid in removing prey from the substrate. They can generate a moderate shock if disturbed and contact is made with the electric organs; the electrical discharges of narcinids have been measured at 8-37 volts, much less than the electric rays of the genus Torpedo.[3] All species are ovoviviparous, with eggs hatching inside the mother.[4]

[edit] Species

There are approximately 27 species in four genera:

[edit] References

  1. ^ Narcinidae (TSN 564006). Integrated Taxonomic Information System. Retrieved on March 20 2006.
  2. ^ "Narcinidae". FishBase. Ed. Rainer Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
  3. ^ a b Martin, R. Aidan. Electric Rays. ReefQuest Centre for Shark Research. Retrieved on October 12, 2008.
  4. ^ a b c d Compagno, L.J.V. and Last, P.R. (1999). Narcinidae. Numbfishes. p. 1433-1437. In: K.E. Carpenter and V.H. Niem (eds.) FAO identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Rome: Food and Agricultural Organization.
  5. ^ Hamlett, William C. (1999). Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes. Baltimore and London: JHU Press. ISBN 0-8018604-8-2. 
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