How to Identify Longspine Squirrelfish

To identify Longspine Squirrelfish (Holocentrus rufus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Predominantly reddish to silvery-red, often with faint longitudinal stripes or lines along the body. The fins are typically reddish, and the dorsal fin often has a white margin or spots.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Very large eyes, characteristic of nocturnal species., A prominent, elongated spine at the angle of the preopercle (cheek bone), which is longer than the eye diameter., A deep notch in the dorsal fin, separating the spiny and soft-rayed portions., Rough, ctenoid scales.

Dorsal fin

XI spines, 14-16 soft rays; deeply notched between spiny and soft-rayed portions.

Tail fin

Deeply forked, with pointed lobes.

Pectoral fin

13-15 rays.

Distinctive fins

Anal fin with IV spines, 9-10 soft rays. Pelvic fins with I spine, 7 soft rays.

Identification Tips

1. 1

   Preopercular Spine

   The most definitive feature is the long, sharp spine at the lower posterior corner of the gill cover (preopercle), which is noticeably longer than the diameter of the eye. This distinguishes it from other squirrelfish species.

2. 2

   Coloration

   Its overall reddish body color, often with subtle horizontal lines, is a good indicator, though color can vary with depth and individual.

3. 3

   Dorsal Fin

   The deeply notched dorsal fin, with 11 strong spines, is characteristic of the genus Holocentrus.

4. 4

   Nocturnal Behavior

   Observing its behavior – hiding during the day and active at night – can also aid in identification in its natural habitat.

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