Like other groupers, this rather wary, coral reef-dwelling fish is a large, robust species. It may be one of two colour forms: the pale black-saddled form is whitish or pale yellowish, with five dark brown to black bars on the head and body. Small blue spots with dark edges may also pattern the body. The other colour form is much darker, being brown, olive, red, or nearly black, speckled with numerous, dark-edged blue spots. The dark bars that appear on the pale form are either very faint or entirely absent in this form. Blacksaddled coral groupers have large mouths, lined with numerous small teeth and prominent canines on the sides of the lower jaw, enabling them to be efficient predators of other reef inhabitants.
As most fish, this species harbours many parasite species. The diplectanid monogeneans Echinoplectanum laeve and Echinoplectanum chauvetorum are parasites on the gills.
Blacksaddled Coral Grouper habitat
This species inhabits outer coral reef slopes between four to 100 metres depth (Heemstra and Randall 1993, Kailola et al. 1993). It feeds mostly on fishes and occasionally crustaceans (Leiske and Myers 1994). It forages over greater areas and depth range than the co-occurring Plectropomus leopardus (Matley et al. 2016). It is a monandric protogynous hermaphrodite (males derived exclusively through sexual transition of mature females; Adams 2002, 2003). It is also a relatively fast-growing species that reaches 50 cm in less than four years with females reaching sexual maturity in under three years (Davies et al. 2006, Heupel et al. 2010). Similar growth rates are recorded from individuals taken from the Western Indian Ocean (Grandcourt 2005). It forms small spawning aggregations (M. Samoilys and H. Choat pers. comm. 2016), but large aggregations were reported from the northern GBR in the 1980's (M. Samoilys pers. comm. 2016). An aggregation of 30 large P. laevis was observed at Moore Reef GBR in 2014 (E. Fisher pers. comm. 2016). It is thought that P. laevis spawns over deeper areas on reef fronts as compared to P. leopardus, which may explain the paucity of spawning observations for P. laevis. Small groups of reproductively active P. laevis have been observed in French Polynesia (Tuamotus), Fiji (Y. Sadovy pers. comm. 2016) and Papua New Guinea (Hamilton 2003). On the Great Barrier Reef (GBR), it has been aged to at least 18 years, an age at maturity of 2.2 years at ~40 cm fork length, the youngest male was nine years of age with transitional individuals occurring at 8-9 years, natural mortality of 0.39 and maximum length of 115 cm (Davies et al. 2006, Heupel et al. 2010). In Aldabra, it has been aged to 20 years (Grandcourt 2005). Based on a longevity of 18 to 20 years, age of first maturity of 2 years, and applying the mean generational turnover formula in Depczynski and Bellwood (2006), one generation length is estimated to range from 10 to 11 years.
Blacksaddled Coral Grouper threats
This species experiences overfishing in some localised areas, but this is not known to be a major threat on a global level. Given the increasing interest in juveniles of this species for the live food trade, there is potential for increased exploitation in the future.