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Taxon profile

species

Frostback Rockcod
Epinephelus bilobatus Randall & Allen, 1987

kingdom Animalia - animals »  phylum Chordata - chordates »  class Actinopterygii - ray-finned fishes »  order Perciformes - perch-likes »  family Serranidae - sea basses and groupers »  genus Epinephelus

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Description

Body depth contained 2.8 to 3.3 times in standard length (for fish 8 to 27 cm standard length). Head length contained 2.4 to 2.6 times in standard length; preopercle subangular, with the serrae at the angle slightly enlarged; opercular spines inconspicuous; upper edge of operculum straight or slightly concave; nostrils subequal in small fish, but rear nostril diameter about twice that of anterior nostril in a fish of 27 cm standard length; maxilla reaches below rear half of eye; midlateral part of lower jaw with 2 rows of small teeth. Gill rakers 7 to 9 on upper limb, 14 to 16 on lower limb, total 23 to 25. Dorsal fin with XI spines and 17 or 18 rays, the third or fourth spine longest (contained 2.1 to 2.5 times in head length) and slightly longer than the longest dorsal-fin ray, the interspinous membranes slightly to moderately incised; anal fin with III spines and 8 rays, the second and third spines subequal, their length contained 2.5 to 3.2 times in head length; pectoral-fin rays 17 to 19; pectoral fins longer than pelvic fins, pectoral-fin length contained 1.5 to 1.8 times in head length; caudal-peduncle depth contained 3.2 to 3.6 times in head length; caudal fin rounded. Lateral-body scales ctenoid; auxiliary scales present or absent; lateral-line scales 48 to 52; lateral-scale series 94 to 102.
Colour: Head and body pale, covered with indistinctly defined, dark orange-brown spots; dark spots extend onto soft dorsal, caudal, and anal fins where the pale interspaces form a network pattern; the spots along the margin of these fins are darker than other spots: a series of 3 bilobed dark blotches or close-set pairs of dark brown to black spots along base of dorsal fin and adjacent body; dorsal part of body of fresh specimens with a pale bluish grey tinge; spinous dorsal fin dusky, with indistinct dark spots and a blackish margin; paired fins also with dark brown spots. Dark brown line in maxillary groove.

Distribution

E. bilobatus has been known only from northwestern Australia. A frozen specimen was purchased in the market at Hengchun, Taiwan; but this fish was from a trawler that had been fishing in foreign waters, and its place of origin could not be determined. However, recently there have been specimens caught, observed, or newly identified in a vast area ranging from eastern coast of India (Chennai, Madras) to Tasman Sea (Middleton Reef, Lord Howe Province).

Ecology

Coral reefs and rocky bottom in depths of 4 to 50 m. There is no published information on the biology of this species.

Size

Maximum total length at least 33 cm.

Interchangeable taxa

E. bilobabtus was illustrated in colour (as "Epinephelus maculatus") by Allen (1985) and Sainsbury et al. (1985). E. bilobatus is one of a group of 9 shallow-water coral reef species that have a rounded caudal fin and close-set dark brown spots with the pale interspaces forming a network on the body. These species have been much confused in the literature, and many museum specimens have been misidentified. The other “reticulated groupers” differ from E. bilobatus as follows:

E. faveatus has the lateral-body scales smooth (except for area covered by pectoral fins), shorter dorsal-fin spines (length of fourth spine contained 2.6 to 3.9 times in head length), and dark spots on body at dorsal-fin base not bilobed or in pairs.

E. hexagonatus has conspicuous white dots on the body between the dark spots, dark spots on body at dorsal-fin base not bilobed or in pairs, dorsal-fin rays 15 to 17, and second anal-fin spine much longer than third spine.

E. macrospilos has the lateral-body scales mostly smooth, pectoral fins dusky with narrow white edge, dark spots on body at dorsal-fin base not bilobed or in pairs and rear edge of caudal fin pale yellow or white.

E. maculatus has the dorsal-fin membranes not incised between the spines; juveniles yellowish brown, with a few small black spots (mainly on head and fins) and a few large irregular white blotches on head, body, and fins; dorsal-fin rays 15 to 17; lateral-scale series 102 to 120.

E. melanostigma has a single black blotch at base of last 4 dorsal-fin spines, dorsal-fin rays 14 to 16, lateral-line scales 56 to 68, and midlateral part of lower jaw with 3 to 5 rows of teeth.

E. merra has dark spots on body at dorsal-fin base not bilobed or in pairs, pectoral fins with small black spots largely confined to the rays, dorsal-fin rays 15 to 17, and fourth to ninth dorsal-fin spines subequal (the longest contained 2.6 to 2.9 times in head length).

E. quoyanus has dark spots on body at dorsal-fin base not bilobed or in pairs, pectoral fins with indistinct dark brown spots, the base with large semicircular dark brown spot edged posteriorly with white, 2 oblique dark brown bands or blotches linked by bands on sides of chest, pectoral-fin length more than 25% of standard length and contained 1.2 to 1.7 times in head length, third to fifth dorsal-fin spines longest and contained 2.3 to 3.0 times in head length.

E. spilotoceps has dorsal-fin rays 14 to 16, lateral-line scales 59 to 69, fourth dorsal-fin spine usually longest (its length contained 2.7 to 3.5 times in head length), 3 brownish black blotches or spots on body at base of dorsal fin but these are not bilobed or in pairs, and caudal-peduncle depth contained 3.7 to 4.3 times in head length.

Sources

Records of The Western Australian Museum, 1987,13 (3): 387-411 Four new Serranid Fishes of the genus Epinephelus (Perciformes: Epinephelinae) from Western Australia, by John E. Randall and Gerald R. Allen.

Food and Agriculture Organization of the United Nations, 1993, Heemstra, P.C.; Randall, J.E., FAO species catalogue. Vol. 16. Groupers of the world (Family Serranidae, Subfamily Epinephelinae). An annotated and illustrated catalogue of the grouper, rock cod, hind, coral grouper and lyretail species known to date.
Author: Petr Čech

Links and literature

CZ AQUATAB. World Wide Web electronic publication [species/8444]

Plíštil J. (Ed.) (2009): AQUATAB. World Wide Web electronic publication [http://aquatab.net] [as Epinephelus bilobatus Randall & Allen, 1987]
Data retrieved on: 17 January 2010
CH DE EN FR IT NL PR SP FishBase [7331]

Froese R., Pauly D. (eds.): FishBase [http://www.fishbase.org]
EN IUCN Red List of Threatened Species 2013.2 [132752]

IUCN Red List of Threatened Species [http://www.iucnredlist.org/] [as Epinephelus bilobatus Randall & Allen, 1987]
Data retrieved on: 27 January 2014

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