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Taxon profile

species

Dwarf Spotted Grouper
Epinephelus merra Bloch, 1793

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

Scientific synonyms

Cephalopholis merra (Bloch, 1793)
Ephinephelus merra Bloch, 1793
Epinephalus merra Bloch, 1793
Serranus merra (Bloch, 1793)

Other names

= Dwarf-spotted Rockcod
= Honeycomb Cod
= Honeycomb Grouper
= Honeycomb Rock Cod
= Honeycomb Rock-cod
= Honeycomb Rockcod
= Honeycombe Grouper
= Wire-netted Reefcod
= Wire-netting Cod

IUCN category:Least Concern

Images

Description

Body depth contained 2.8 to 3.3 times in. standard length (for fish 10 to 22 cm standard length). Head length contained 2.3 to 2.6 times in standard length; interorbital area flat, the dorsal head profile convex: preopercle rounded or subangular, the serrae at angle enlarged; upper edge of operculum almost straight; nostrils subequal or rear nostrils larger; maxilla reaches past vertical at rear edge of eye; midlateral part of lower jaw with 2 to 4 rows of teeth, the inner teeth about twice the length of outer ones. Gill rakers 6 to 9 on upper limb, 14 to 17 on lower limb. Dorsal fin with XI spines and 15 to 17 rays, the third to last spines subequal, the longest contained 2.4 to 3.2 times in head length: anal fin with III spines and 8 rays, the second spine subequal to the third,its length contained 2.1 to 3.0 times in head length and much longer than depth of peduncle; pectoral-fin rays 16 to 18; pectoral-fin length contained 1.5 to 1.8 times in head length; pelvic-fin length contained 1.8 to 2.2 times in head length; caudal-peduncle depth contained 3.2 to 4.1 times in head length; caudal fin rounded. Lateral body scales ctenoid, with auxiliary scales; lateral-line scales 48 to 54; lateral-scale series 98 to 114. Pyloric caeca 8.
Colour: Head, body, and fins pale, covered with close-set, dark brown or reddish brown spots, the interspaces forming an irregular pale reticulum; spots on ventral part of body paler, more widely spaced and diffuse in outline; some midlateral spots often joined to form horizontal bands; 5 irregular dark bars can be displayed by differential darkening of some body spots, but black dorsal blotches never present; dark spots on median fins become smaller towards the fin margin; pectoral fins covered with distinct small black spots, largely confined to the rays (the best diagnostic colour character for E. merra); tips of interspinous dorsal-fin membranes white or pale yellow, with a small submarginal black spot.

Distribution

E. merra is widely distributed in the Indo-Pacific region from South Africa to French Polynesia in the central Pacific. Except in the western Indian Ocean, where it is known (but not common) along the African coast from Kenya to South Africa (juveniles occur south to Port Alfred), E. merra seems to be an insular species. It is not known from the Red Sea, Persian Gulf, or Asian mainland. It occurs at most (probably all) of the tropical islands in the Indian Ocean. In the Pacific, it ranges from Japan to Australia (from Western Australia to New South Wales) and Lord Howe Island and eastward to the Tuamotu Archipelago. It occurs at most Pacific islands, both on and off the Pacific Plate, but it is not found at the Hawaiian Islands (although its introduction there has been attempted), Marquesas, Pitcairn Group, or at Easter Island.

Ecology

E. merra is a shallow-water coral reef species and is typically found around patch reefs in lagoons and bays.It is usually seen in depths less than 20 m, but is occasionally found as deep as 50 m. Randall and Brock (1960) found that 68% of the fish with food in their stomach had eaten crustaceans (primarily crabs) and 29% contained fishes. But during periods when postlarval fishes were settling out on the reef, E. merra fed mainly on these small fishes. Harmelin-Vivien and Bouchon (1976) determined that juveniles (at Madagascar) fed more on crustaceans (brachyurans, 63% by weight) than on fishes (35%), but in adults these proportions were reversed (22% brachyurans and 68% fishes and 8% cephalopods). This increase of piscivory with age is common in groupers. These authors also found that brachyurans were the most common prey at night, and fishes were taken more often during the day. At Okinawa in Japan, Sano et al. (1984) examined the prey of 12 E. merra that contained food; they found a preference for crabs (50%) and blenniid fishes (25%). Randall (1955) provided evidence that this species is a protogynous hermaphrodite: of 1 067 fish examined, all of the small adults (less than 16 cm standard length) were females; the average size of adult males was 20 cm, and the largest was 25 cm standard length; the mean for adult females was 16 cm, and the largest was 21 cm standard length. The gonads of some fish contained both testicular and ovarian tissue. At the Society Islands, E. merra spawn between January and April for 3 or 4 days af the time of the full moon. Like most groupers, this species spends its entire life in one small area. Of 1 000 fish tagged at Moorea, 45 were recovered over a period of two years; except for some fish that were displaced from the capture site, none showed any significant movement from their home reef. A 10 cm marked specimen released on 15 January 1968 at Oahu, Hawaiian Islands, was 24 cm total length when it was recaptured on 14 July 1971.

Size

E. merra attains a maximum of 26 cm standard length (about 32 cm total length).

Interchangeable taxa

E. merra is one of the “reticulated groupers,” which comprise 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. E. merra can be distinguished from the other reticulated groupers by its pectoral-fin pattern of conspicuous black dots that are largely confined to the rays of the fin. Other differences between E. merra and the reticulated groupers are as follows:

E. bilobatus has 3 bilobed dark blotches or close-set pairs of dark brown spots on body and base of dorsal fin, dark spots-on median fins not much smaller distally, and dorsal-fin rays 17 or 18.

E. faveatus has the lateral-body scales smooth (except for area covered by pectoral fins), longest anal-fin spine contained 3.6 to 4.3 times in head length, dark bands on the chest, and 83 to 98 lateral-scale series.

E. hexagonatus has conspicuous white dots on the body between the dark spots, 4 or 5 brownish black blotches on body at base of dorsal fin, a large olive-brown spot or band just behind eye, and lateral-line scales 61 to 70.

E. macrospilos has the lateral-body scales mostly smooth and the pectoral fins dusky with narrow white edge.

E. maculatus has the interspinous dorsal-fin membranes not incised, third or fourth dorsal-fin spine longest (its length contained 2.1 to 2.6 times in head length and longer than dorsal-fin rays); and juveniles are yellowish brown with irregular white blotches on the body.

E. melanostigma has a large black blotch at base of last 4 dorsal-fin spines, length of second anal-fin spine not longer than caudal-peduncle depth, and lateral-line scales 56 to 68.

E. quoyanus has the pectoral fins with indistinct dark brown spots and the base with a large semicircular dark brown spot edged posteriorly with white, 2 oblique dark brown bands or blotches linked by bands on sides of chest, dorsal-fin rays 16 to 18, and third to fifth dorsal-fin spines longest (length contained 2.4 to 3.0 times in head length).

E. spilotoceps has dark spots on the snout very small (about the size of the nostrils), 3 black blotches at base of dorsal fin and another on top of caudal peduncle, and lateral-line scales 59 to 69.

Sources

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/8494]

Plíštil J. (Ed.) (2009): AQUATAB. World Wide Web electronic publication [http://aquatab.net] [as Epinephelus merra Bloch, 1793]
Data retrieved on: 17 January 2010
CH DE EN FR IT NL PR SP FishBase [4923]

Froese R., Pauly D. (eds.): FishBase [http://www.fishbase.org]

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