Plectropomus areolatus (Rüppell, 1830)

Species Nomenclature

The squaretail coral grouper, Plectropomus areolatus (Rüppell, 1830), has an elongated body.

Body Size

Individuals reaching first maturity measure approximately 36.65 cm in length and weigh around 771.2 grams, and the species can reach a maximum total length of 80 cm, with females typically growing longer than males.

Fin Spine and Ray Count

This species has 7 to 8 dorsal spines and 10 to 12 soft dorsal rays, while its anal fin has 3 spines and 8 soft rays.

Jaw Dentition

It has between 1 and 4 canines on the upper jaw.

Caudal Fin Shape

Its caudal fin, or tail, is truncated, ending in a straight vertical edge – this feature gives the species its common name.

Body Coloration

Squaretail coral groupers display a wide range of possible coloration, from whitish gray with dark spots, to greenish-gray, to a red and brown patterned body.

Fin Coloration

All of its fins are dark brown.

Pacific Distribution

This grouper is found across the western Pacific Ocean, including waters surrounding Japan, southeastern China, the Philippines, Indonesia, and Australia.

Indian Ocean Distribution

It also occurs in the Indian Ocean near East Africa.

Reef Habitat Preference

It inhabits shallow, coral-rich lagoonal and seaward reef areas, particularly channels along the reef front.

Depth Range

It is commonly found widely across coral reefs or rocky reefs in tropical and subtropical waters, and typically occurs at depths between 1 and 70 meters in the marine neritic zone, the nearshore marine environment extending to 200 meters along the continental shelf.

Home Range Size

Squaretail coral groupers have small home ranges, and most individuals stay close to their aggregation site, with dispersing larvae spreading out within a 14.4 kilometer radius.

Aggregation Site Proximity

Their aggregation sites are located relatively close to one another.

Aggregation Species Composition

Of 32 studied grouper aggregations, 59% of squaretail coral groupers formed aggregations at sites shared with other grouper species, while 41% formed single-species aggregations.

Co-Aggregating Species

The species often co-aggregates with camouflage groupers and brown-marbled groupers, but it also maintains aggregation sites that are only used by its own species.

Single-Species Aggregation Habitat

At some of these single-species sites, squaretail coral groupers aggregate on low-relief reef habitats that do not appear able to support aggregations of the other co-occurring species.

Peak Spawning Season

The peak spawning season for the squaretail coral grouper runs from January to April, lasting for 2 to 3 months total.

Lunar Spawning Correlation

Spawning events occur during new and full moons, which may suggest a connection to associated high tidal variation and flow to improve larval dispersal or retention.

Lunar Periodicity Reliability

However, similar to water temperature, consistent lunar periodicity is not a reliable indicator of spawning timing, and the species shows reproductive variability relative to lunar cycles.

Temperature Spawning Predictability

While some regional similarities exist, water temperature profiles also cannot be used reliably to predict spawning, because the water temperatures recorded during reproductive periods vary between locations.

Year-Round Aggregation Frequency

Spawning aggregations form monthly year-round.

Aggregation Reproductive Indicators

The purpose of these aggregations is spawning, indicated by observed color changes, fighting, quivering, and the presence of multiple gravid females.

Spawning Aggregation Arrival Pattern

When aggregating to spawn, males usually arrive either individually or in small groups to establish territories, and they arrive earlier than females.

Female Arrival Pattern

Females generally arrive in large schools.

Maturity and Lifespan

Squaretail coral groupers reach sexual maturity at around 2.8 years of age and have an average lifespan of approximately 10 years.

Early Life Stage

After hatching from an egg, the species begins life as a planktonic larva before maturing into an adult fish.

Hermaphroditism Hypothesis

There has been some proposed evidence of protogynous hermaphroditism, or sex change from female to male, in this species.

Hermaphroditism Evidence

Evidence for this theory comes from gonad tissue that may contain both male and female sexual organs, testes and ovaries.

Initial Hermaphroditism Study

One early study found that 18 out of 448 sampled individuals were transitioning from female to male.

Hermaphroditism Theory Status

A later follow-up found potential errors in the original study, leaving the theory of protogynous hermaphroditism in this species unresolved.