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Overview

Comprehensive Description

Biology

Found on open sandy or silty substrates of lagoon and seaward reefs. Often buries itself and easily overlooked. Uses pectoral fins to startle predators and shows color during courtship (Ref. 48635). Feeds on small fishes and crustaceans (Ref. 9710). The venom of this fish can be deadly to man. Its ability to camouflage itself by living half-buried presents a real danger. Solitary on sand and mud bottoms (Ref 90102).
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Distribution

Inimicus didactylus is widely distributed in the eastern Indian and western Pacific oceans; however, the species is more common in regions around the Andaman Islands, northern Australia, China, and the Phillipines.

Biogeographic Regions: oriental (Native ); australian (Native )

  • Wheeler, A. 1985. The world encyclopedia of fishes. London: Macdonald.
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Indo-West Pacific: Thailand to Vanuatu, north to the Ryukyu Islands (Ref. 559) and southeast China, south to Australia.
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West Pacific and southeastern Indian Ocean.
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Physical Description

Morphology

Inimicus didactylus has an elongate body and is without scales, with the exception of 13-15 buried in the lateral line. It is covered with skin glands that have the appearance of warts. No minimums or maximums in length are reported in the literature, but specimens seem to range approximately between 130 mm to 200 mm.

The species has a depressed head that is strongly concave on the dorsal side. The head is also covered with flaps of skin and raised ridges, and tentacles are present on the head, trunk, and fins. Its mouth points up almost vertically, and its eyes protrude visibly outwards. A raised knob at the end of its snout gives it the appearance of having an upturned nose.

The pectoral fins are large and their coloration is significant in identifying the different species of Inimicus. In I. didactylus, the underside of the pectoral fins bears broad dark bands (containing smaller, lighter spots) at the basal and distal ends. The lower 2 rays of its pectoral fins are free from the rest of the fin and used in "walking" along the bottom. This coloration is not sexually dimorphic. The caudal fin has dark bands at basal and subterminal positions. The dorsal fin is composed of 15 to 17 spines and 7 to 9 rays. With the exception of the first 3, the spines are almost entirely incised from membrane.

Other Physical Features: bilateral symmetry ; venomous

  • Herre, A. 1951. A review of scorpaenoid fishes of the Phillipines and adjacent seas. The Phillipine Journal of Science, 80: 381-482.
  • Mandritsa, S. 1991. New species of the genus Inimicus (Scorpaeniformes, Synanceiidae) from the Coral Sea. Journal of Icthyology, 31: 76-79.
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Dorsal spines (total): 15 - 17; Dorsal soft rays (total): 7 - 9; Analspines: 2; Analsoft rays: 10 - 12
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Size

Maximum size: 215 mm TL
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Max. size

25.0 cm TL (male/unsexed; (Ref. 48635))
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Diagnostic Description

Body colors highly variable and best identified by the patterns on the fins (Ref. 48635). Lower 2 pectoral rays are entirely free and used as "walking" legs and the inner face of the fin is brightly colored (Ref. 37816).Description: Characterized by dark mottling and spots on body; inner black zone with white streaks on inside surface of pectoral fin, with whitish middle zone and outer zone of grey to yellow with pale spots; first three dorsal spines broadly connected with membrane, remaining spines with membrane on less than basal one-third; slightly elevated eyes; absence of scales; longer snout than postorbital length; depth of body about 3.5-3.8 in SL (Ref. 90102).
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Body colors highly variable and best identified by the patterns on the fins (Ref. 48635). Lower 2 pectoral rays are entirely free and used as "walking" legs and the inner face of the fin is brightly colored (Ref. 37816).Description: Characterized by dark mottling and spots on body; inner black zone with white streaks on inside surface of pectoral fin, with whitish middle zone and outer zone of grey to yellow with pale spots; first three dorsal spines broadly connected with membrane, remaining spines with membrane on less than basal one-third; slightly elevated eyes; absence of scales; longer snout than postorbital length; depth of body about 3.5-3.8 in SL (Ref 90102).
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Type Information

Type for Inimicus didactylus
Catalog Number: USNM 98905
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Preparation: Illustration
Year Collected: 1909
Locality: Ragay Gulf, Canmahala Bay; Between Burias and Luzon, Luzon, Philippines, Philippine Archipelago, Canmahala Bay, Ragay Gulf, Pacific
Vessel: Albatross
  • Type:
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Ecology

Habitat

Depth range based on 17 specimens in 1 taxon.
Water temperature and chemistry ranges based on 9 samples.

Environmental ranges
  Depth range (m): 0.915 - 89
  Temperature range (°C): 23.246 - 28.954
  Nitrate (umol/L): 0.057 - 1.738
  Salinity (PPS): 33.821 - 35.568
  Oxygen (ml/l): 4.191 - 4.855
  Phosphate (umol/l): 0.080 - 0.336
  Silicate (umol/l): 0.987 - 6.358

Graphical representation

Depth range (m): 0.915 - 89

Temperature range (°C): 23.246 - 28.954

Nitrate (umol/L): 0.057 - 1.738

Salinity (PPS): 33.821 - 35.568

Oxygen (ml/l): 4.191 - 4.855

Phosphate (umol/l): 0.080 - 0.336

Silicate (umol/l): 0.987 - 6.358
 
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This species is found in tropical marine regions, particularly brackish water. It is a benthic species that generally occupies moderately deep waters up to 70 m, although it has been reported at depths as shallow as 5 m and as deep as 450 m. It is associated with mangrove swamps and coral reefs.

Range depth: 5 to 450 m.

Habitat Regions: tropical ; saltwater or marine

Aquatic Biomes: reef ; brackish water

Wetlands: swamp

  • Munro, I. 1967. The fishes of New Guinea. New Guinea: Department of Agriculture, Stock, and Fisheries.
  • Myers, R. 1999. Micronesian reef fishes: a field guide for divers and aquarists. Barrigada, Territory of Guam: Coral Graphics.
  • Weber, M., L. de Beaufort. 1962. The fishes of the Indo-Australian archipelago. Leiden, Netherlands: E.J. Brill.
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Environment

reef-associated; brackish; marine; depth range 5 - 80 m (Ref. 37816)
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Depth range based on 17 specimens in 1 taxon.
Water temperature and chemistry ranges based on 9 samples.

Environmental ranges
  Depth range (m): 0.915 - 89
  Temperature range (°C): 23.246 - 28.954
  Nitrate (umol/L): 0.057 - 1.738
  Salinity (PPS): 33.821 - 35.568
  Oxygen (ml/l): 4.191 - 4.855
  Phosphate (umol/l): 0.080 - 0.336
  Silicate (umol/l): 0.987 - 6.358

Graphical representation

Depth range (m): 0.915 - 89

Temperature range (°C): 23.246 - 28.954

Nitrate (umol/L): 0.057 - 1.738

Salinity (PPS): 33.821 - 35.568

Oxygen (ml/l): 4.191 - 4.855

Phosphate (umol/l): 0.080 - 0.336

Silicate (umol/l): 0.987 - 6.358
 
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Depth: 5 - 40m.
From 5 to 40 meters.

Habitat: reef-associated.
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Trophic Strategy

Inimicus didactylus is mainly piscivorous. It lies partially buried in the seafloor with its eyes protruding above the substrate waiting to ambush smaller fishes. Its natural coloration allows it to blend in seamlessly with its environment, making it more difficult for its prey to visually spot it. Rows of teeth lining its jaws and vomer facilitate in feeding I. didactylus.

Primary Diet: carnivore (Piscivore )

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Found inshore (Ref. 75154).
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Associations

Inimicus didactylus acts as a predator in its ecosystems. It is likely that is is host to a multitude of parasites, but there have been no investigations on this subject for this particular species. Given the sensitivity of host specificity in many parasitic organisms, few conjectures can be made across species concerning the parasites of the commercially popular Inimicus japonicus and I. didactylus.

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Like other Synancejidae, I. didactylus possesses a powerful venom that is stored in glands at the bases of its dorsal spines that can be injected upon contact. As described above, this species also flashes the undersides of its pectoral fins when disturbed as a warning signal. These, in addition to its natural camouflage, discourage other organisms from feeding on it.

No known predators of I. didactylus are listed.

Anti-predator Adaptations: aposematic ; cryptic

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Life History and Behavior

Behavior

Inimicus didactylus flashes the bright undersides of its pectoral fins as a warning to predators when disturbed. Specialized for its benthic habitat, it has 2 feeler rays on its pectoral fins that probe the seafloor and allow it to "walk" along the bottom. Its eyes and nostrils are located above its dorsal profile as another benthic specialization.

Perception Channels: tactile ; chemical

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Life Cycle

In I. didactylus juveniles, the distinctive pigmentation of the pectoral fins does not appear until they have reached a length of about 50 to 60 mm.

Additional information concerning the development of I. didactylus is unavailable, however there are details on the juvenile stages of the larger order, Scorpaeniformes. When larvae hatch, they come equipped with fully developed eyes, range in length from 1.5 to 2.3 mm, and have large yolk sacs. As the larvae develop further, they take on the characteristics of two general morphs: preflexion and postflexion. The former is more elongate and slender than the latter with larger development of the pectoral fins.

  • Leis, J., D. Rennis. 1984. The Larvae of Indo-Pacific Coral Reef Fishes. Honolulu: University of Honolulu Press.
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Life Expectancy

Lifespan of this species has not been measured.

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Reproduction

There is little information available on the mating systems of I. didactylus.

There is little information on the reproductive cycle of this species; however, reef scorpaenids generally lay small (0.7 to 1.2 mm) clusters of spherical or slightly ovoid eggs in gelatinous sac-like structures. (An exception to this is Inimicus japonicus, which lays larger, single eggs.)

There is little information on parental investment in I. didactylus.

  • Leis, J., D. Rennis. 1984. The Larvae of Indo-Pacific Coral Reef Fishes. Honolulu: University of Honolulu Press.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Inimicus didactylus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1
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Conservation

Conservation Status

Little is known about the abundance of this species, but it is not generally considered in need of special conservation efforts. This species is not listed in IUCN's Red List.

US Federal List: no special status

CITES: no special status

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Threats

Not Evaluated
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Relevance to Humans and Ecosystems

Benefits

Inimicus didactylus is feared by those who come in contact with it due to its painful, venomous spines and resemblence to more deadly stonefishes. Because it is so well concealed, swimmers or divers may accidentally brush against it. It is also commonly caught by prawn trawlers.

Negative Impacts: injures humans (bites or stings, venomous )

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Not enough information has been gathered on this species' effect on the ecosystem to evaluate its impact.

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Importance

aquarium: commercial
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Wikipedia

Inimicus didactylus

Inimicus didactylus, also known as Demon Stinger or Devil Stinger, is a member of the Inimicus genus of venomous fishes, closely related to the true stonefishes. It can reach a body length of 25 cm (10 in) and is irregularly surfaced with spines and a knobby appearance. The fish has venomous spines to ward off enemies. The fish are nocturnal, and often dig themselves partially into the sandy seabed during the day. The body is red or sandy yellow and well camouflaged on sandy and coral seabeds.

Physical description[edit]

Inimicus didactylus

I. didactylus adults can attain a body length of up to 26 centimeters in length. The body color is red or sandy yellow with light blotches, and very similar to that of the surrounding sandy or coral seabed in which they are found. This coloration acts as a camouflage which renders them extremely difficult to detect in their natural habitat. The skin is without scales except along the lateral line, and is covered with venomous spines and wartlike glands which give it a knobby appearance. The head is flattened, depressed and concave. The eyes, mouth and nostrils project upwards and outwards from the dorsal aspect of the head. Sexual dimorphism is not believed to occur in this species.

Fin morphology:

  • dorsal fin: composed of 15 to 17 spines and 7 to 9 soft rays.[1]
  • caudal fin: composed of 2-4 spines and 4-14 soft rays, with dark bands at basal and subterminal positions.
  • pelvic fin: composed of one spine and 3-5 soft rays.
  • pectoral fin: composed of 10-12 rays. The two most caudal rays of each pectoral fin are detached from the rest of the fin, and angled in a ventral direction. The fish employ these two rays to prop up the forward part of their body, as well as to "walk" along the bottom of the substrate.[2][3][4][5] The ventral surface of the pectoral fins bears broad black bands containing smaller, lighter spots at the basal and distal ends. In I. filamentosus, these bands are attenuated, while the bands of I. sinensis have yellow spots on them. This is a key feature for distinguishing the two species, which are otherwise nearly identical.[3]

Behavior[edit]

I. didactylus is a piscivorous ambush predator. It is nocturnal and typically lies partially buried on the sea floor or on a coral head during the day, covering itself with sand and other debris to further camouflage itself. It has no known natural predators. When disturbed by a scuba diver or a potential predator, it fans out its brilliantly colored pectoral and caudal fins as a warning. Once dug in, it is very reluctant to leave its hiding place. When it does move, it displays an unusual mechanism of subcarangiform locomotion — it crawls slowly along the seabed, employing the four lower rays (two on each side) of its pectoral fins as legs.[2][3][4][5]The Bearded ghoul has poisonous dorsal fish spines that can cause a painful wound.

See also[edit]

References[edit]

  1. ^ Mandritsa, S.A. (1991). "New species of the genus Inimicus (Scorpaeniformes, Synanceiidae) from the Coral sea". J. Ichthyol 31 (2): 76–79. 
  2. ^ a b William A. Gosline (July 1994). "Function and structure in the paired fins of scorpaeniform fishes". Journal Environmental Biology of Fishes 40 (3): 219–226. doi:10.1007/BF00002508. Retrieved 2010-03-22. 
  3. ^ a b c World Database of Marine Species: Spiny devil fish. Accessed 03-22-2010.
  4. ^ a b Scott Michael (Winter 2001). "Speak of the devil: fish in the genus Inimicus". SeaScope 18. Retrieved 2010-03-27. 
  5. ^ a b WetWebMedia.com: The Ghoulfish/Scorpion/Stonefishes of the Subfamily Choridactylinae (Inimicinae), by Bob Fenner. Accessed 03-27-2010.
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