Overview

Comprehensive Description

Biology

Benthopelagic over coral and rock (Ref. 58302). Occurs singly or in aggregations along clear seaward and outer lagoon reefs and channels (Ref. 37816). Feeds in midwater on zooplankton (Ref. 90102).
  • Randall, J.E. and L.J. Bell 1992 Naso caesius, a new acanthurid fish from the Central Pacific. Pac. Sci. 46(3):344-352. (Ref. 9944)
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Distribution

Range Description

Naso caesius is known from Palau, Mariana Islands, northern Marshall Islands, Hawaiian Islands, Great Barrier Reef, Osprey Reef, and Chesterfield Islands in the Coral Sea, New Caledonia, Fiji, Tuvalu, Society Islands and Pitcairn Islands. It is also recorded from Kavieng, Papua New Guinea (Hamilton et al. 2004), Christmas Island (Hobbs et al. 2010) and Cocos Keeling.
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Pacific Ocean: Northern Marianas, Marshall Islands, Hawaiian Islands, Pitcairn group, Society Islands (French Polynesia), Australia and New Caledonia.
  • Randall, J.E. and L.J. Bell 1992 Naso caesius, a new acanthurid fish from the Central Pacific. Pac. Sci. 46(3):344-352. (Ref. 9944)
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Western Pacific, antiequatorial: Micronesia and Marshall Islands east to Hawaiian Islands; Queensland (Australia) and New Caledonia east to Tonga, Society Islands and Pitcairn Group.
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Physical Description

Morphology

Dorsal spines (total): 6 - 7; Dorsal soft rays (total): 27 - 30; Analspines: 2; Analsoft rays: 28 - 31
  • Myers, R.F. 1999 Micronesian reef fishes: a comprehensive guide to the coral reef fishes of Micronesia, 3rd revised and expanded edition. Coral Graphics, Barrigada, Guam. 330 p. (Ref. 37816)
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Size

Maximum size: 456 mm SL
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Max. size

45.6 cm SL (male/unsexed; (Ref. 9944))
  • Randall, J.E. and L.J. Bell 1992 Naso caesius, a new acanthurid fish from the Central Pacific. Pac. Sci. 46(3):344-352. (Ref. 9944)
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Diagnostic Description

Bluish grey to grey-brown, capable of displaying a colour pattern of vertically elongate blotches (lighter or darker than ground colour) on side and upper part of body. Opercular and preopercular margins not dark brown. Caudal fin uniform in colour. Gill rakers on lower limb of gill arches entirely pale. Edge of lower lip not white (Ref 9808).Description: Characterized further by absence of horn or protuberance; caudal peduncle with pair of bony plates, blade-like keels not pointed; greatest depth of body 2.5-3.0 in SL (Ref. 90102).
  • Myers, R.F. 1999 Micronesian reef fishes: a comprehensive guide to the coral reef fishes of Micronesia, 3rd revised and expanded edition. Coral Graphics, Barrigada, Guam. 330 p. (Ref. 37816)
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Type Information

Paratype for Naso caesius Randall & Bell
Catalog Number: USNM 140088
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Preparation: Unknown
Collector(s): V. Brock, K. Emory & T. Kohler
Year Collected: 1946
Locality: Marshall Islands: Bikini Atoll, coral head within the Atoll at the following position: 11 deg 33' 13" N. Lat; 165 deg 28' 39" E. Long., Bikini Atoll, Ralik Chain, Marshall Islands, Pacific
Depth (m): 9 to 14
  • Paratype: Randall, J. E. & Bell, L. J. 1992. Pacific Science. 46 (3): 347, 2.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Naso caesius is usually seen in aggregations on drop-offs, sometimes in mixed schools with N. hexacanthus. A few schools were observed in Christmas Island, all the N. hexacanthus seen were with N. caesius (J.H. Choat pers. comm. 2010). This species prefers oceanic conditions - clear water along steep dropoffs, offshore reefs and pinnacles (R.F. Myers pers. comm. 2010).

Reproduction

The sexes are separate among the acanthurids (Reeson 1983). Sexual dimorphism is differentiated with males having larger caudal spines (J.H. Choat pers comm. 2010). Nuptial males were observed to flash different colours (R.F. Myers pers. comm. 2010).
In Papua New Guinea, it is known to form spawning aggregations in open water above the reef every month of the year during the first and third quarter moon phase. It was reported to spawn early morning and late afternoon with group and pair spawning observed. N. caesius is reported to aggregate bimonthly, just prior to the new and full moons. Several hundred species were observed to spawn (Hamilton et al. 2004).

Systems
  • Marine
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Environment

reef-associated; marine; depth range 15 - 50 m (Ref. 90102)
  • Allen, G.R. and M.V. Erdmann 2012 Reef fishes of the East Indies. Perth, Australia: Universitiy of Hawai'i Press, Volumes I-III. Tropical Reef Research. (Ref. 90102)
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Depth range based on 23 specimens in 1 taxon.
Water temperature and chemistry ranges based on 23 samples.

Environmental ranges
  Depth range (m): 8 - 61
  Temperature range (°C): 25.709 - 28.529
  Nitrate (umol/L): 0.151 - 1.522
  Salinity (PPS): 34.443 - 35.312
  Oxygen (ml/l): 4.406 - 4.727
  Phosphate (umol/l): 0.130 - 0.254
  Silicate (umol/l): 1.409 - 4.599

Graphical representation

Depth range (m): 8 - 61

Temperature range (°C): 25.709 - 28.529

Nitrate (umol/L): 0.151 - 1.522

Salinity (PPS): 34.443 - 35.312

Oxygen (ml/l): 4.406 - 4.727

Phosphate (umol/l): 0.130 - 0.254

Silicate (umol/l): 1.409 - 4.599
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
Choat, J.H., Abesamis, R., Clements, K.D., McIlwain, J., Myers, R., Nanola, C., Rocha, L.A., Russell, B. & Stockwell, B.

Reviewer/s
Edgar, G. & Kulbicki, M.

Contributor/s

Justification
Naso caesius is widespread throughout the west and south central Pacific but not yet reported from the rest of the Coral Triangle Region. It is harvested in the Guam fishery and in Papua New Guinea. There is no evidence of population declines from harvesting. It occurs in marine reserves in parts of its range. It is therefore listed as Least Concern.
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Population

Population
Naso caesius is uncommon in the American Samoa National Park (National Park of Samoa Checklist of Fishes accessed 21 April 2010). In Christmas Island, this species is common (Hobbs et al. 2010) and is the dominant Naso sp. (J.H. Choat pers. comm. 2010). It accounts for 2% of the Acanthurid fishery in Guam (Division of Aquatic and Wildlife Resources unpub. data) but is absent in the Saipan fishery in 2008 (P. Houk unpub. data).

Population Trend
Stable
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Threats

Major Threats
There are no major threats known for this species.

Surgeonfishes show varying degrees of habitat preference and utilization of coral reef habitats, with some species spending the majority of their life stages on coral reef while others primarily utilize seagrass beds, mangroves, algal beds, and /or rocky reefs. The majority of surgeonfishes are exclusively found on coral reef habitat, and of these, approximately 80% are experiencing a greater than 30% loss of coral reef area and degradation of coral reef habitat quality across their distributions. However, more research is needed to understand the long-term effects of coral reef habitat loss and degradation on these species' populations. Widespread coral reef loss and declining habitat conditions are particularly worrying for species that recruit into areas with live coral cover, especially as studies have shown that protection of pristine habitats facilitate the persistence of adult populations in species that have spatially separated adult and juvenile habitats (Comeros-Raynal et al. 2012).
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Least Concern (LC)
  • IUCN 2006 2006 IUCN red list of threatened species. www.iucnredlist.org. Downloaded July 2006.
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Management

Conservation Actions

Conservation Actions
There are no species-specific conservation measures in place for this species. However, its distribution overlaps several marine protected areas within its range.
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Wikipedia

Naso caesius

Naso caesius, the gray unicornfish,[2] is a tropical fish found in coral reefs in the Pacific Ocean.[3]

References[edit]

  1. ^ Common names for Naso caesius at www.fishbase.org.
  2. ^ Common names for Naso caesius at www.fishbase.org.
  3. ^ Naso caesius at www.fishbase.org.


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