Rhadinesthes decimusSlender snaggletooth

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Geographic Range

Specimens of Rhadinesthes decimus have been collected in the tropical Indian Ocean, the southern Atlantic Ocean, the eastern and western south Pacific Ocean, and the central north Pacific Ocean. In the south Atlantic Ocean, the range of Rhadinesthes decimus seems to stop around 27 degrees south of the equator. In the North Pacific, the range of this animal seems to be to the east of 21 degrees west and to the north of 20 degrees north. (Fugii, 1984; Gibbs, 1984; Gibbs, 1990)

Habitat

Rhadinesthes decimus is known primarily as a mesopelagic ocean fish living at depths around 500 m. According to Gibbs (1990), it is characteristic of members from this family (Stomiidae) to live at depths deeper than 500 m during the day and to migrate closer to the ocean surface during the night. (Gibbs, 1984; Gibbs, 1990)

Rhadinesthes decimus has been found in both tropical waters (i.e. the Indian Ocean) and temperate waters (i.e. the northern and southern Atlantic and Pacific Oceans). (Bigelow, et al., 1964; Gibbs, 1984; Gibbs, 1990)

  • Range depth
    100 to 600 m
    328.08 to 1968.50 ft
  • Average depth
    500 m
    1640.42 ft

Physical Description

The body of Rhadinesthes decimus is described as long and slender, reaching lengths of up to 410 mm (Gibbs, 1990). This species is distinguished from other closely related members of the family Stomiidae by the line of luminous material that begins behind the post-orbital organ and continues along the side of the body for most of its length. Rhadinesthes decimus also has a barbel that extends about half the length of the head and has photophores and luminous material near the stem. (Bigelow, et al., 1964; Fugii, 1984; Gibbs, 1984; Gibbs, 1990)

The dorsal fin on this fish has 11 to 13 rays. The fin's origin is relatively far behind the pelvic fin insertion. There is no dorsal adipose fin present on Rhadinesthes decimus (Bigelow et al., 1964). The ventral adipose fin is long and low, extending from the back of the pelvic bone to the anus. The lower caudal rays are also greatly elongated. The color of Rhadinesthes decimus tends to be black except for the line of luminous material. (Bigelow, et al., 1964; Fugii, 1984; Gibbs, 1984)

There are no fangs present in the mouth of this fish. Rather, the teeth of Rhadinesthes decimus tend to be relatively small. On the upper jaw, these teeth are widely spaced and some are slightly curved. There are usually between 10 and 12 teeth on the premaxillary and between 14 and 30 teeth on the maxillary. Rhadinesthes decimus also has small gill teeth. (Bigelow, et al., 1964; Fugii, 1984; Gibbs, 1984)

  • Range length
    79 to 410 mm
    3.11 to 16.14 in

Development

We have no information about the development of Rhadinesthes decimus.

Reproduction

We have no information about mating behavior in Rhadinesthes decimus.

We have very little information about reproduction in this species. One source (FishBase 2004) classifies this species has having low reproductive resilience, meaning that the time it would take for a population of these fish to double is between 4.5 and 14 years. There is little additional information available. ()

We have no information about parental investment by Rhadinesthes decimus.

Lifespan/Longevity

There is currently little or no information about this topic regarding Rhadinesthes decimus.

Behavior

There is currently little information about the behavior of Rhadinesthes decimus.

The species is suspected to migrate vertically, moving up at night and down during the day, presumably following its prey. Specimens of other related species have been taken in shallow waters at night. (Gibbs, 1984)

Communication and Perception

While there is little known about the communication and perception of Rhadinesthes decimus, several sources state in the physical description of this animal that it has a line of luminous material on its body as well as luminous material at the stem of the barbel near its mouth. Though no sources make an effort to explain these luminous structures, we presume that they are used to communicate, perhaps to lure prey, confuse predators, or signal other individuals of R. decimus.

The species has fairly large eyes, so we can presume that vision is important, and all fish use chemical senses to some extent, but further details on sensory information in this species are not documented. (Bigelow, et al., 1964; Gibbs, 1984)

  • Communication Channels
  • visual

Food Habits

According to Gibbs, the feeding habits of Rhadinesthes decimus are still poorly known, but it is assumed that they feed on midwater fishes and crustaceans (1984). (Gibbs, 1984)

  • Animal Foods
  • fish
  • aquatic crustaceans

Predation

There is currently no published information about predators of Rhadinesthes decimus. It's possible that the bioluminescent structures on these fish are used to confuse or distract predators.

Ecosystem Roles

Rhadinesthes decimus is an intermediate predator. It's relations with other species in the deep-water pelagic ecosystems have not been studied.

Economic Importance for Humans: Positive

There is currently little or no information about this topic regarding Rhadinesthes decimus.

Economic Importance for Humans: Negative

There is currently little or no information about this topic regarding Rhadinesthes decimus.

Conservation Status

The wide distribution of occurrences of this species suggest that it may occur in large populations, but there are no studies determining the actual population size of Rhadinesthes decimus, much less its conservation status. Given this absence of information, it is not surprising that the species is not listed on any major lists of threatened or endangered species.

Other Comments

Rhadinesthes decimus was first formally described in 1911 by Erich Zugmayer.

Many classification systems put Rhadinesthes decimus in the family Astronesthidae. However, according to Fink, the most appropriate classification scheme puts Rhadinesthes decimus in the Stomiidae family (1985). Furthermore, common synonyms for Rhadinesthes decimus are Rhadinesthes jacobssoni, Rhadinesthes lucberti, and Astronesthes decimus. All of these synonyms describe the same species Rhadinesthes decimus (Bigelow et al., 1964 and Gibbs, 1984). (Bigelow, et al., 1964; Fink, 1985; Gibbs, 1984)

Contributors

George Hammond (editor), Animal Diversity Web.

Michael O'Neill (author), University of Michigan-Ann Arbor, William Fink (editor, instructor), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

photic/bioluminescent

generates and uses light to communicate

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Bigelow, H., D. Cohen, M. Dick, R. Gibbs, M. Grey, J. Morrow, L. Schultz, V. Walters. 1964. Fishes of the Western North Atlantic. New Haven: Sears Foundation for Marine Research, Yale University.

Fink, W. 1985. Phylogenetic Interrelationships of the Stomiid Fishes (Teleostei: Stomiiformes). Ann Arbor, MI: The University of Michigan.

Fugii, E. 1984. Rhadinesthes decimus. Pp. 437 in H Masuda, K Amaoka, C Araga, T Uyeno, T Yoshino, eds. The Fishes of the Japanese Archipelago. Tokyo, Japan: Tokai University Press.

Gibbs, R. 1990. Astronesthidae. Pp. 300-307 in J Quero, J Hureau, C Karrer, A Post, L Saldanha, eds. Check-list of the Fishes of the Eastern Tropical Atlantic (Clofeta I). Paris, France: UNESCO.

Gibbs, R. 1984. Astronesthidae. Pp. 325-335 in P Whitehead, M Bauchot, J Hureau, J Nielson, E Tortonese, eds. Fishes of the North-Eastern Atlantic and the Mediterranean. Paris: UNESCO.