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Species: Aluterus monoceros, Unicorn filefish

All Families:   All Genera:   All Species:

grey +/- dark blotches
juv: pale lines around dark spots
tail base: depth < length
C: < snout, edge straight
head profiles: upper convex, lower concave

Aluterus monoceros (Linnaeus, 1758)

Unicorn filefish

Body a very compressed elongated oval; a long pointed snout, snout profiles of adult - upper convex, lower concave; a small mouth that opens above center line; teeth moderately strong, six in outer row on top jaw and six or less on outer row on bottom jaw; gill opening a short slit on side before pectoral base; 2 dorsal fins, 1st with II spines, 1st long, slender, smooth, over eye, erectile, can be locked in position by minute 2nd spine; second dorsal fin 46-50 rays; anal rays 47-52; pectoral rays modally 14; median fins rays unbranched; tail base longer than deep (depth 65-95% of its length); tail fin usually shorter than snout,  18-26% of SL, with straight to slightly concave edge; pelvic fins absent, no scales encasing area where pelvics should be; scales minute, innumerable, like fine hairs, give skin a rough texture, like sandpaper;  no patch of enlarged scales above pectoral base; lateral line inconspicuous.

Pale grey to grey-brown; brown spots and blotches on upper side; dorsal and anal pale yellowish brown; tail membranes dark brown; juveniles & sometimes young adults with network of pale lines enclosing darker spots and blotches.

Size: 76 cm.

Habitat: rocky and soft bottom habitats.

Depth: 0-150 m.

Circumtropical; Massachusetts to Brazil.

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  • Marine
  • Marine Only
  • Inshore
  • Inshore Only
Water Column Position
  • Bottom
  • Bottom only
  • Reef (rock/coral/oyster)
  • Water column
  • Reef associated (reef + edges-water column & soft bottom)
  • Soft bottom (mud/sand/gravel/beach/estuary/mangrove/seagrass)
  • Reef and soft bottom
  • Corals
  • Flotsam
FishBase Habitat
  • Reef Associated
Feeding Group
  • Omnivore
  • Corallivore
  • Data
  • Mobile benthic crustacea (shrimps/crabs)
  • Hard corals
  • Data
  • Benthic microalgae
  • Soft corals/hydroids
Egg Type
  • Data
  • Benthic
  • Pelagic larva
Global Endemism
  • Circumtropical ( Indian + Pacific + Atlantic Oceans)
  • Greater Caribbean non-endemic
  • All species.
Regional Endemism
  • Extends N + S of GC
  • Continent
  • All species..
  • Extends North of GC
  • GC non-endemic
  • Extends South of GC
  • Continental primarily
  • Island (s)
  • Continent + Island (s)
  • Also in Brazil
  • Resident
Climate Zone
  • Tropical (10-23N, Nicaragua / Cuba)
  • Subtropical (23-35N, Florida / Carolinas / Bermuda)
  • Temperate (>35N)
  • Equatorial (0-10N, Costa Rica / Venezuela)
IUCN Red List
  • Listed
  • Least concern
  • Not listed
Depth Range Min
  • 0
Depth Range Max
  • 150
Length Max
  • 76