Small juveniles (<8 cm) with small hexagonal spots on head and body becoming larger posteriorly and on vertical fins; distinguished by pale yellowish brown color with five vertical series of irregular dark brown blotches; head, body and fins with numerous close-set, small brown spots; caudal peduncle with small black saddle dorsally; cycloid scales except ctenoid in juvenile; body with auxiliary scales; moderately deep bodied, greatest depth 2.6-2.9 in SL; pelvic fins 2.1-2.4 in head length; further characterized by having head length 2.3-2.5 times in SL; flat or slightly concave interorbital area; adults dorsal head profile indented at eyes and distinctly convex from there to origin of dorsal fin; rounded preopercle, finely serrate; distinctly convex upper edge of operculum, descending almost vertically to rear end of operculum; deeply indented anterior edge of preorbital bone below nostrils; triangular posterior nostrils, 4-7 times larger than anterior nostrils in adults; maxilla extends well posterior to eye; 3-4 rows of teeth on midlateral part of lower jaw, inner teeth twice as long compared to outer teeth; canines inconspicuous; nostrils are close together.
Brown-marbled grouper's Feeding
Feeds on fishes, crabs, and cephalopods. May be ciguatoxic in some areas.
Brown-marbled grouper habitat
Adults of this species inhabit lagoon pinnacles, patch reefs, channels and outer reef slopes in clearwater, coral-rich areas. Juveniles inhabit seagrass beds and estuarine or low salinity inshore areas. Its maximum total length is 120 cm. It utilizes migratory corridors to reach spawning aggregation sites (a travel distance of up to 25 km), and males tend to arrive prior to females. Spawning aggregations are typically formed in channels, patch reefs and outer reef pinnacles at depths from 3 to greater than 70 m in areas ranging in size from 16 to 175 km² (Rhodes et al. 2012, Rhodes et al. 2013, Waldie et al. 2016). Aggregations tend to form consistently relative to specific lunar cycles (several each year), with individuals resident at the site for up to 14 days (Sadovy de Mitcheson 2011, Rhodes et al. 2012). Spawning aggregation sites are known from the Seychelles (Bijoux et al. 2013), British Indian Ocean Territory, Kenya, Palau (Western Channel, Ebiil and Ulong), Pohnpei (Micronesia), Melanesia (Papua New Guinea and Solomon Islands), outside the Great Barrier Reef Marine Park (Australia), Komodo National Park (Indonesia), Dumbea (New Caledonia) and Fiji.
In Australia, the size at 50% sexual maturity for females is 57 cm fork length and about 9 years of age, with a maximum reported age of 42 years (Pears et al. 2006, Mapleston et al. 2009). Based on a longevity of 42 years, age of first maturity of 9 years, and applying the mean generational turnover formula in Depczynski and Bellwood (2006), one generation length is estimated to be 25.5 years.
Heavy exploitation of spawning aggregations and take of juveniles from wild stocks for aquaculture grow-out are major threats to this species. Secondary threats include the degradation of seagrass beds and coral reefs due to coastal development and climate change (Burke et al. 2002).