How to Identify Planehead Filefish

To identify Planehead Filefish (Monacanthus hispidus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Highly variable, ranging from mottled brown, gray, green, to yellowish, often with irregular spots, blotches, or lines that allow for excellent camouflage. Can change color rapidly to match its surroundings. The caudal fin often has a dusky bar or spots.

Scale type

none

Mouth position

terminal

Distinctive features

Rough, sandpaper-like skin due to small, bristly scales., A prominent, erectile first dorsal spine located above the eye, which can be locked into an upright position by a smaller second spine., Small, puckered mouth with incisor-like teeth., Pelvic fin reduced to a spine-like structure, often with a dewlap of skin.

Dorsal fin

Two dorsal fins; the first with 1-2 spines (the first spine is large and erectile, the second very small and locks the first), the second with 30-37 soft rays. The soft dorsal fin is long and low.

Tail fin

Rounded to slightly truncate caudal fin with 12 rays.

Pectoral fin

Small, rounded pectoral fins with 12-14 rays.

Distinctive fins

Anal fin similar in shape and size to the soft dorsal fin, with 31-37 soft rays. Pelvic fin reduced to a single, rough spine, often with a prominent dewlap of skin that can be extended or retracted.

Identification Tips

1. 1

   First Dorsal Spine

   Look for the prominent, erectile first dorsal spine located directly above the eye. This spine can be locked upright and is a key characteristic of filefishes.

2. 2

   Skin Texture

   Observe the skin, which is rough and sandpaper-like due to numerous small, bristly scales. This distinguishes it from smooth-skinned fishes.

3. 3

   Coloration and Pattern

   Note the highly variable, mottled coloration that allows for camouflage. Patterns often include irregular spots, blotches, or lines. The ability to rapidly change color is also a good indicator.

4. 4

   Pelvic Fin

   Examine the pelvic fin, which is reduced to a single, rough spine, often accompanied by a prominent dewlap of skin that can be extended or retracted.

5. 5

   Mouth

   The small, puckered mouth with incisor-like teeth is characteristic of its feeding habits on small invertebrates and algae.

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