Chromis xouthos, a new species of damselfish (Pomacentridae) from the East Andaman Sea and Central Indian Ocean

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1 aqua, Journal of Ichthyology and Aquatic Biology Chromis xouthos, a new species of damselfish (Pomacentridae) from the East Andaman Sea and Central Indian Ocean Gerald R. Allen 1 and Mark V. Erdmann 2 1) Department of Aquatic Zoology, Western Australian Museum, Francis Street, Perth, Western Australia ) Conservation International Indonesia Marine Program, Jl. Dr. Muwardi No. 17, Renon, Denpasar Indonesia Accepted: Keywords Taxonomy, marine fishes, Indian Ocean, Pomacentridae, Chromis, new species Abstract Chromis xouthos is described from six specimens, mm SL, collected at Pulau Weh, Aceh Province, Sumatra, Indonesia at a depth of 25 m. Diagnostic features include: XIII,12 dorsal rays; II,11 (rarely 12) anal rays; 19 (rarely 18) pectoral rays; 3 spiniform caudal rays; tubed lateral line scales; (total, 26-28) gill rakers on the first branchial arch; body depth in SL; and colour in life mainly golden brown with a yellowish caudal fin and pale bluish-grey pelvic fins. It appears to be closely related to C. pembae of the western Indian Ocean and Red Sea, but exhibits apparent modal differences in the number of total gill rakers on the first branchial arch, tubed lateral line scales, and pectoral rays. The two species share similar colour patterns, although C. xouthos is overall golden brown compared with the dark brown ground colour of C. pembae. Zusammenfassung Beschrieben wird Chromis xouthos auf der Grundlage von sechs Exemplaren mit 82,4-92,3 mm SL, die bei Pulau Weh, Provinz Aceh, Sumatra, Indonesien in einer Tiefe von 25 m gefangen wurden. Zu den Unterscheidungsmerkmalen gehören XIII, 12 Rückenflossenstrahlen; II, 11 (selten 12) Afterflossenstrahlen; 19 (selten 18) Brustflossenstrahlen; 3 stachelförmige Schwanzflossenstrahlen; röhrenförmige Seitenlinienschuppen; (insges ) Kiemenreihen auf dem ersten Kiemenbogen; eine Körpertiefe von 1,9-2,0 in SL; sowie eine überwiegend goldbraune Lebendfärbung mit gelblicher Schwanzflosse und blass bläulich grauen Bauchflossen. Die neue Art scheint C. pembae vom westlichen Indischen Ozean und Roten Meer nahe verwandt zu sein, unterscheidet sich aber deutlich durch die hohe Gesamtzahl an Kiemenreihen auf dem ersten Bogen, die röhrenförmigen Seitenlinienschuppen und die Brustflossenstrahlen. Beide Arten haben ein ähnliches Farbmuster, doch ist C. xouthos grundsätzlich goldbraun, während C. pembae eine dunkelbraune Grundfarbe besitzt. Résumé Chromis xouthos est décrit sur base de six spécimens, de 82,4-92,3 mm LS, collectés à Pulau Weh, province d Aceh, Sumatra, Indonésie, à une profondeur de 25 m. Les données diagnostiques comportent: XIII, 12 rayons dorsaux; II, 11 (rarement 12) rayons à l anale; 19 (rare - ment 18) rayons pectoraux; 3 rayons spiniformes à la caudale; écailles canaliculées de la ligne latérale, (total de 26-28) branchiospines sur le premier arc branchial; hauteur du corps 1,9-2,0 en LS; et la couleur in vivo principalement brun or avec une caudale jaunâtre et des pelviennes d un gris-bleu pâle. L espèce semble très proche de C. pembae de l Océan Indien et de la Mer Rouge, mais présente des différences modales dans le nombre total de branchiospines sur le premier arc branchial, des écailles canaliculées sur la ligne latérale et des rayons pectoraux. Les deux espèces arborent des patrons de coloration semblables, quoique C. xouthos soit brun or partout comparé à la couleur de base brun foncé de C. pembae. Sommario Chromis xouthos è descritta sulla base di sei esemplari, mm SL, raccolti a Pulau Weh, Aceh Province, Sumatra, Indonesia alla profondità 25 m. Caratteristiche diagnostiche sono: XIII,12 raggi dorsali; II,11 (raramente 12) raggi anali; 19 (raramente 18) raggi pettorali; 3 raggi caudali spiniformi; scaglie tubulari della linea laterali; (totale, 26-28) rastrelli branchiali sul primo arco branchiale; altezza del corpo in SL; e colorazione vitale principalmente bruno dorato con pinna caudale giallastra e pinne pelviche grigio-bluastro pallido. Sembra strettamente imparentata con C. pembae dell Oceano Indiano occidentale e Mar Rosso, ma si differenzia per il valore modale dei rastrelli branchiali totali sul primo arco branchiale, le scaglie della linea laterale e i raggi pettorali. Le due specie hanno livrea simile, sebbene C. xouthos è completamente bruno dorata rispetto al colore bruno scuro di C. pembae. 89 aqua vol. 10 no

2 Chromis xouthos, a new species of damselfish (Pomacentridae) from the East Andaman Sea and Central Indian Ocean Introduction The pomacentrid genus Chromis Cuvier is abundant on coral and rocky reefs throughout tropical and warm temperate seas. It is one of the major plankton feeding groups and large swarms of midwater feeding Chromis form an integral part of most local reef fish communities. The genus, which currently contains 86 valid species, is the largest in the family. Allen (1991) provided photos and a brief diagnosis for 75 of the 76 described species (C. dispilus from New Zealand unintentionally omitted). Since that time, an additional nine species were described by Randall and McCosker (1992); Moura (1995); Randall (1988 and 2001), and Allen and Randall (2004). In addition, Allen (1993) showed that C. megalopsis, which he described (1976) from Western Australia is a junior synonym of C. mirationis Tanaka of southern Japan. The present paper describes a new species that was collected by the authors at Pulau Weh, a small mountainous island off the north-western tip of Sumatra. We were invited to conduct a reef assessment survey of the island by Conservation International, four months after the tragic Sumatran tsunami of 26 December Methods Lengths of specimens are given as standard length (SL) measured from the anterior end of the upper lip to the base of the caudal fin (posterior edge of hypural plate); head length is measured from the same anterior point to the posterior edge of the opercle flap; body depth is the maximum depth taken vertically between the belly and base of the dorsal spines; body width is the maximum width just posterior to the gill opening; snout length is measured from the anterior end of the upper lip to the anterior edge of the eye; orbit diameter is the horizontal fleshy diameter, and interorbital width the least fleshy width; upper jaw length is taken from the front of the upper lip to the posterior end of the maxilla; caudal peduncle depth is the least depth, and caudal peduncle length is the horizontal distance between verticals at the rear base of the anal fin and the caudal fin base; lengths of fin spines and rays are measured to their extreme bases (i.e., not from the point where the ray or spine emerges from the basal scaly sheath); caudal fin length is the horizontal length from the posterior edge of the hypural plate to a vertical at the tip of the longest ray; caudal concavity is the horizontal distance between verticals at the tips of the shortest and longest rays; pectoral fin length is the length of the longest ray; pelvic fin length is measured from the base of the pelvic spine to the filamentous tip of the longest soft ray; pectoral ray counts include the small splint-like, uppermost rudimentary ray; only the tubebearing anterior lateral line scales are counted; a separate count is given for the deeply pitted scales occurring in a continuous series midlaterally on the caudal peduncle; the decimal figure 5 appearing in the scale row count above and below the lateral line refers to a small truncated scale at the respective bases of the dorsal and anal fins; gill raker counts include all rudiments and are presented as separate counts for the upper and lower limbs as well as a combined count; the last fin ray element of the dorsal and anal fins is usually branched near the base and is counted as a single ray. Counts and proportions appearing in parentheses apply to the range for the paratypes if different from the holotype. Proportional measurements expressed as percentage of the standard length are provided in Table I. Type specimens are deposited at Pusat Penelitian dan Pengembangan Oseanologi, Jakarta, Indonesia (NCIP), United States National Museum of Natural History, Washington, D.C. (USNM), and Western Australian Museum, Perth (WAM). Chromis xouthos n. sp. Figs. 1-2; Tables I and II Holotype: NCIP 6301, 92.3 mm, Pulau Weh, Aceh Province, Sumatra, Indonesia: patch reef off Teupinpineung Point ( N, E), at depth of 25 m, collected with spear, G. R. Allen and M. Erdmann, 5 May Paratypes: NCIP 6302, 82.4 mm, Pulau Weh, Indonesia: Lhok Weng Bay, purchased from fishermen, G. R. Allen and M. Erdmann, 10 May 2005; WAM. P , 2 specimens, mm, collected with holotype; USNM , 2 specimens, mm, collected with holotype. Diagnosis Dorsal rays XIII,12; anal rays II,11 (rarely 12); pectoral rays 19 (rarely 18); spiniform caudal rays 3; tubed lateral line scales 16-17; gill rakers (total, 26-28); body depth in SL; colour in life mainly golden brown with yellowish caudal fin and pale bluish-grey pelvic fins. Description Dorsal rays XIII,12; anal rays II,11 (one paratype with II,12); all dorsal and anal soft rays branched, the last to base; pectoral rays 19 (one paratype with 18), the upper lowermost pair unbranched; pelvic rays I,5; principal caudal rays 15, the upper and lowermost unbranched; spiniform caudal rays 3, followed by 2 accessory segmented rays; scales in longitudinal series 27; tubed lateral line scales 16 (16-17); posterior midlateral scales with a deep pit (in continuous series) 8 (6-9); scales above lateral line to origin of dorsal fin 2.5; scales above lateral line to base of middle dorsal spine 1.5; scales below lateral line to origin of anal fin 8; gill rakers = 26 ( = 26-28); branchiostegal rays 6; supraneural (predorsal) bones 3; vertebrae aqua vol. 10 no

3 Gerald R. Allen and Mark V. Erdmann Body moderately deep, depth 2.0 ( ) in SL, and compressed, width 2.7 ( ) in body depth; head length 3.4 (3.2) in SL; snout shorter than orbit diameter, its length 3.4 ( ) in head length; orbit diameter 2.8 ( ) in head; interorbital space convex, its width 2.9 ( ) in head; caudal peduncle depth 2.0 ( ) in head; caudal peduncle length 2.5 ( ) in head. Mouth terminal, small, and oblique, forming an angle of about 40 to horizontal axis of head and body; posterior edge of maxilla reaching vertical at anterior edge of pupil or slightly behind this point, upper jaw length 2.7 ( ) in head; teeth multiserial, with outer row of conical teeth in each jaw, largest anteriorly; 26 upper and 23 lower teeth on each side of jaw of holotype; a narrow band of villiform teeth lingual to outer row, in 2-3 irregular rows anteriorly, narrowing to single row on side of jaws; tongue triangular with rounded tip; gill rakers long and slender, longest on lower limb near angle about three-fourths length of longest gill filaments; nostril with slight fleshy rim, more elevated on posterior edge and located at level of middle of pupil, slightly less than one-third distance from front of snout to base of upper lip. Opercle ending posteriorly in flat spine, with its tip relatively obtuse and obscured by large scale; margin of preopercle distinctly concave and mainly smooth except for few weak crenulations on lower angle, with upper posterior margin extending dorsally to level of upper edge of pupil, and lower margin extending to level of anterior edge of orbit; suborbital with free lower margin extending nearly to vertical at posterior pupil edge. Scales finely ctenoid; anterior lateral line ending beneath rear portion of spinous dorsal fin; head scaled except lips, tip of snout, and narrow zone from orbit to edge of snout containing nostrils; scaly sheath at base of dorsal and anal fins, about two-thirds pupil diameter at base of middle of spinous portion of dorsal fin, progressively narrower on soft portion; column of scales on each membrane of dorsal and anal fins, narrowing distally, those on spinous portion of dorsal progressively longer, reaching about two-thirds distance to spine tips on posterior membranes, then progressively shorter on soft portion; small scales on caudal fin extending slightly more than two-thirds distance to posterior margin; small scales on basal one-fifth of pectoral fins; median scaly process extending posteriorly from between base of pelvic fins, its length about three-fifths that of pelvic spine; axillary scale above base of pelvic spine also about three-fifths length of pelvic spine. Origin of dorsal fin over third lateral line scale, the Fig. 1. Chromis xouthos, freshly collected holotype, NCIP 6301, 92.3 mm SL, Pulau Weh, Indonesia. Photo by M. V. Erdmann. 91 aqua vol. 10 no

4 Chromis xouthos, a new species of damselfish (Pomacentridae) from the East Andaman Sea and Central Indian Ocean Table I. Proportional measurements of selected type specimens of Chromis xouthos as percentage of the standard length. Holotype Paratype Paratype Paratype Paratype Paratype NCIP WAM USNM WAM USNM NCIP 6301 P P Standard length (mm) Body depth Body width Head length Snout length Orbit diameter Interorbital width Depth of caudal peduncle Length of caudal peduncle Upper jaw length Predorsal distance Preanal distance Prepelvic distance Length of dorsal fin base Length of anal fin base Pectoral fin length Pelvic fin length Pelvic fin spine length st dorsal spine th dorsal spine Last dorsal spine Longest soft dorsal ray st anal spine nd anal spine Longest soft anal ray Caudal fin length Caudal concavity Fig. 2. Chromis xouthos, underwater photograph of adult, approximately 120 mm total length, Pulau Weh, Indonesia. Photo by G. R. Allen. aqua vol. 10 no

5 Gerald R. Allen and Mark V. Erdmann Table II. Comparison of total gill rakers on first branchial arch, pectoral fin ray, and tubed lateral line scales for Chromis xouthos and C. pembae. Total gill rakers Species C. xouthos C. pembae Pectoral rays LL scales Species C. xouthos C. pembae predorsal distance 2.4 ( ) in SL; base of soft portion of dorsal fin contained 2.9 times in base of spinous portion; first dorsal spine 5.1 ( ) in head; seventh to ninth dorsal spines longest and subequal, length 2.0 ( ) in head; last dorsal spine 2.2 ( ); membranes of spinous portion of dorsal fin moderately incised; third-fourth dorsal soft ray longest, 1.4 ( ) in SL; first anal spine 3.7 ( ) in head; second anal spine 1.4 ( ) in head; first 4-5 anal soft rays subequal, longest 1.5 ( ) in head; caudal fin deeply forked, its length 3.1 ( ) in SL, with caudal concavity 2.2 ( ) in head; fourth pectoral ray longest, 2.8 ( ) in SL; pelvic spine 1.7 ( ) in head; first soft ray of pelvic fin with short filament at tip, barely reaching to origin of anal fin if not damaged, 3.4 ( ) in SL. Colour in life: golden brown with yellowish caudal fin; chin, breast, and belly pale bluish grey; soft dorsal and anal fins with horizontally ovate brownish spot at base of posterior 6-7 rays; also anterior edge of anal fin brown; pelvic fins pale bluish grey, sometimes with slight yellow hue on basal half; a small, scarcely noticeable, brown spot on dorsal surface of pectoral fin base; a narrow yellowish ring around pupil; upper lip pale tan, the lower greyish; lacrimal (preorbital) and suborbital series silver grey. A nest guarding individual (presumably a male) seen at Pulau Weh, exhibited a bleached overall tan pattern (including caudal fin), lacking the normal golden hue. Fish from the central Indian Ocean (Maldives and Chagos) differ slightly in having a white rather than yellowish caudal fin. Colour in alcohol: after one month in preservative body still similar to live coloration except less golden and more brownish, darker on upper back; chin, isthmus, and scale margins of breast dusky on holotype and some paratypes; dorsal and anal spines blackish; central portion spinous dorsal fin and basal part of soft Fig. 3. Chromis pembae, underwater photograph of juvenile, approximately 100 mm total length, Gulf of Aqaba, Red Sea. Photo by G. R. Allen. 93 aqua vol. 10 no

6 Chromis xouthos, a new species of damselfish (Pomacentridae) from the East Andaman Sea and Central Indian Ocean dorsal fin charcoal or blackish; large, horizontally ovate blotch at base of posterior half of anal fin; distal two-thirds of soft dorsal and anal fins semitranslucent whitish; caudal fin pale tan to whitish; pelvic fins dusky brown; pectoral fins semitranslucent whitish with small brown spot at uppermost part of base. Etymology The new species is named xouthos (Greek: yellowish-brown) with reference to the overall coloration. Comparisons The new species appears to be most closely related to C. pembae Smith (1960) from the Red Sea and western Indian Ocean (Fig. 3). The two species have the same general shape and share similar colour patterns, although C. xouthos is overall golden brown compared with the dark brown ground colour of C. pembae. Although it would be desirable to eventually compare more specimens, there are also apparent modal differences in the number of total gill rakers on the first branchial arch, tubed lateral line scales, and pectoral rays (see Table II). We have examined 12 specimens of C. pembae, mm SL, from the Gulf of Aqaba, Red Sea, deposited at BPBM. Distribution and ecology Thus far known only from the Similan Islands off the Andaman Sea coast of Thailand (G. R. Allen observation), Pulau Weh off the northern tip of Sumatra, Maldive Islands (Kuiter, 1998), and Chagos Archipelago (identified from a photograph). It can be expected to occur at the Andaman and Nicobar Islands, and probably at the Mergui Archipelago, off Myanmar. The species is usually encountered in clear water over coral reefs at depths between about 12 and at least 45 m. Pulau Weh habitats included both gradually sloping bottoms and steeper drop-offs, but in the former case it was restricted to depths greater than 20 m in the vicinity of isolated, small patch reefs. It generally forms aggregations ranging from just a few fish to at least individuals, which feed on plankton up to several metres above the bottom. The fish retreat to caves, crevices, and ledges when approached closely by divers. The species was common off the northern tip of Seulako Island, a satellite islet off the north-western peninsula of Pulau Weh. Numerous individuals were encountered adjacent to a steep slope that continued from shore to at least 60 m. Most fish were seen at depths between 15 and 30 m. References Allen, G. R Two new species of damselfishes (Pomacentridae) from Western Australia. Records of the Western Australian Museum, 4 (2): Allen G. R Damselfishes of the World. Aquarium Systems, Mentor, Ohio, 271 pp. Allen, G. R Two new species of damselfishes (Pomacentrus), with comments on the validity of two additional pomacentrid fishes. Revue Française Aquariologie, 20 (1): Allen, G. R. & J. E. Randall Two new species of damselfishes (Pomacentridae: Chromis) from Indonesian seas. aqua, Journal of Ichthyology and Aquatic Biology, 9 (1): Moura, R. L. de A new species of Chromis (Perciformes: Pomacentridae) from the southeastern coast of Brazil, with comments on other species of the genus. Revue Française Aquariologie, 21 (3-4): Randall, J. E Three new Indo-Pacific damselfishes of the genus Chromis (Pomacentridae). Memoirs of the Museum of Victoria, 49 (1): Randall, J. E. & J. M. McCosker Two new damselfishes of the genus Chromis (Perciformes: Pomacentridae) from the South Pacific. Proceedings of the California Academy of Sciences, 47 (12): Smith, J. L. B Coral fishes of the family Pomacentridae from the western Indian Ocean and the Red Sea. Ichthyological Bulletin No. 19, Department of Ichthyology, Rhodes University, Grahamstown: , 8 pls. Acknowledgements We are grateful to Conservation International- Indonesia, particularly Jatna Supriatna and Ketut Sarjana Putra, for providing the opportunity to visit Pulau Weh. Defy Pada of Manado assisted us with collections, and the Lumba Lumba Diving Centre provided excellent logistical support for our survey. aqua vol. 10 no