Chauliodus sloani
Sloan's fangfish

Chauliodus sloani, commonly called Sloane’s viperfish or Sloane’s fangfish, are known to inhabit almost all marine waters in the temperate and tropical zones. Their range extends from about 63 ° N to 50 ° S. There are a few regions in the Atlantic, Indian, and Pacific Ocean north of the equator where there have been no records of Sloane’s viperfish (Gibbs, 1984). Chauliodus sloani have been found in the Mediterranean and other adjoining seas as well (Gibbs, 1984). (Gibbs, 1984)

Chauliodus sloani are primarily bathypelagic fish. The bathypelagic region extends from 1000 to 2000 meters below the surface in the open ocean. They have been collected from a maximum depth of 2800 meters (Butler et al., 2001). Chauliodus sloani engage in asynchronous diel vertical migration which means that during the night they can be found in less deep regions such as the mesopelagic, which generally characterizes the depth range of 200 to 1000 meters (Sutton and Hopkins, 1996). It is thought that Sloane’s viperfish prefer regions of higher dissolved oxygen content because other relatives such as Chauliodus pammelas have more highly developed gills (Butler et al., 2001). (Butler et al., 2001; Sutton and Hopkins, 1996)

Sloane’s fangfish are very slender with a maximum length of 35 centimeters (Gibbs, 1984). These iridescent fish come in shades of blue, green, black, or silver. Chauliodus sloani have an adipose fin and a forked caudal fin and their dorsal fin is positioned right behind the head (Gibbs, 1984). Almost all of the fins contain soft rays. The first soft ray of the dorsal fin is elongated and extends to about half the length of the body (McGrouther, 2003). These fish have approximately 2.4 % lipid content in their body (Gibbs, 1984). This low lipid content and the fact that they vertically migrate indicate that Chauliodus sloani probably have some form of swim bladder (Gartner, Crabtree and Sulak, 1997). Members of the genus Chauliodus are believed to eat at least once every 12 days which suggests a relatively low basal metabolic rate (Butler et al., 2001). The lower jaw protrudes beyond the upper jaw and both are lined with fang-like teeth which give the fish its common name. There are rows of 24 or more photophores (light-producing cells) along the lateral and ventral surface of the fish (Butler et al., 2001). They are not sexually dimorphic. (Butler et al., 2001; Gartner, Crabtree, and Sulak, 1997; Gibbs, 1984; McGrouther, 2003)

The larvae of Chauliodus sloani are similar in appearance to the leptocephalus of eels and are approximately 6 millimeters long when hatched. When they double in size the pectoral and caudal fins begin to develop (Gibbs, 1984). It is not known how long Chauliodus sloani take to grow from the larval stage to the adult form. (Gibbs, 1984)

Due to the difficulty of studying them in the wild, there is very little data on the lifespan of Sloane’s viperfish. Studies of the bands in the otoliths (plates in the inner ear) have yielded an estimated longevity of 15 to 30 years for most deep-sea fishes. However, it's difficult to know whether these bands occur strictly at annual intervals (Haedrich, 1997). Chauliodus sloani specimens have been contained in captivity for as long as 12-18 hours (Christophe, Baguet and Marechal, 1979). (Christophe, Baguet, and Marechal, 1979; Haedrich, 1997)

Chauliodus sloani inhabit depths that make them very difficult to study. For this reason, very little is known about their behavior. As mentioned above, they vertically migrate during the night. Many fish do this to improve their chances of finding food and to avoid predators that could normally see them during the day. However, in an asynchronous diel pattern, only some individuals migrate and the depths of migration may vary. It is noted that larger specimens of Chauliodus sloani tend to reside at a greater average depth than smaller specimens (Butler et al., 2001). (Butler et al., 2001)

Home Range

Chauliodus sloani are not known to have a specific home range. This is due to the difficulty in studying them in their own environment.

Since the eyes are rather large in Sloane's viperfish, it is presumed that they have retained use of sight as a form of perception (Gartner, Crabtree and Sulak, 1997). Chauliodus sloani, like other deep-water fish, also probably make use of their bioluminescent photophores to communicate with other conspecifics (Christophe, Baguet and Marechal, 1979). (Christophe, Baguet, and Marechal, 1979; Gartner, Crabtree, and Sulak, 1997)

Sloane’s viperfish have some characteristics typical of deep-water fishes which aid in acquiring food in regions of low light. These features include a straight intestine and an elongated, distensible stomach (Gartner, Crabtree and Sulak, 1997). They also have a relatively large gape, and hinged fangs. This specialized dentition can rotate inward to prevent prey from escaping and ease its passage into the gullet (Gartner, Crabtree and Sulak, 1997). Another feature that is unique to the genus Chauliodus is a hinged connection between the skull and backbone that rotates the skull upward to allow further manipulation of large prey into the throat (Gartner, Crabtree and Sulak, 1997). Chauliodus sloani prey on a variety of nektonic, planktonic, and benthic organisms. This includes other bony fishes and crustaceans. Some examples of nektonic prey include Cyclothone, Bregmaceros, Diaphus, Lampanyctus, and Myctophum (Gibbs, 1984). Larger specimens of Sloane’s fangfish are believed to be exclusively piscivorous while the smaller or younger fish consume a higher ratio of marine arthropods (Butler et al., 2001). Chauliodus sloani are known to be able to prey on fish that are 63 % of their own body length (Butler et al., 2001). These fish acquire food by arching their elongated first dorsal ray over the head and in front of the mouth as a lure (Gartner, Crabtree and Sulak, 1997). They may use their photophores to attract prey as well (McGrouther, 2003). As asynchronous diel migrators, they are presumed to wait at depths that act as common passages for other vertical migrators and catch prey as they ascend to feed (Gartner, Crabtree and Sulak, 1997). (Butler et al., 2001; Gartner, Crabtree, and Sulak, 1997; Gibbs, 1984; McGrouther, 2003)

Chauliodus sloani are preyed upon by larger bathy- and mesopelagic nekton. Remains of Sloane’s viperfish have been found in the stomach of Coryphaena hippurus, some mammalian dolphins (Lagenodelphis, Stenella) and various sharks (Centroscymnus, Galeus). Many species of the family Merlucciidae have been known to prey on Chauliodus sloani as well (Gibbs, 1984). The dark colorings and lack of light at very great depths are the only known sources of protection against predators. These anti-predator characteristics couple with an asynchronous pattern of diel migration to help Chauliodus sloani avoid being eaten (Butler et al., 2001). (Butler et al., 2001; Gibbs, 1984)

Sloane’s fangfish function as higher-trophic level predators in their ecosystem (Gartner, Crabtree, and Sulak, 1997). They are considered to be very important contributors to the predation on myctophids (Butler et al., 2001). Chauliodus sloani serve as prey for the few types of organisms mentioned above. (Butler et al., 2001; Gartner, Crabtree, and Sulak, 1997)

Despite their fearsome appearance, Chauliodus sloani are considered to be harmless to humans. As noted above, this is due to the rare occurrence of contact with humans (Gibbs, 1984). (Gibbs, 1984)

Chauliodus sloani have no known positive impact on humans. Their deep water range limits any type of contact with humans on a regular basis other than the few that are caught in deep water trawls. Since they are among the most common stomiids caught, they provide an opportunity for research on bioluminescence in the deep sea and the behavior of other deep-sea fish (Sutton and Hopkins, 1996). (Sutton and Hopkins, 1996)

Chauliodus sloani are not on the IUCN Red List and are not known to have any specific conservation status (Gibbs, 1984). It would be suspected that due to the deep-water range of this stomiid, it is very difficult to characterize the overall population of this species. There is probably very little impact from humans that would cause any negative conservation status for Chauliodus sloani. (Gibbs, 1984)

Sloane’s viperfish were first identified by Bloch and Schneider in 1801 (McGrouther, 2003). The genus name Chauliodus (for which nine different species are known) comes from the Greek words chaulios which means “open-mouthed” and odous which refers to “teeth” (Gibbs, 1984). (Gibbs, 1984; McGrouther, 2003)