Japan. J. Ichthyol. 魚 類 学 雑 誌 41 (1): 23-28, 1 9 94 41 (1): 23-28, 1 9 94

Record of the Bothid Flounder Asterorhombus fijiensis from the Western Pacific, with Observations on the Use of the First Dorsal-fin Ray as a Lure

Kunio Amaoka,1Hiroshi Senou2and Atsushi Ono3 Laboratoryof MarineZoology, Faculty of Fisheries, Hokkaido Univers -1-1 Minato-cho, Hakodate,Hokkaido 041, Japan 2KanagawaPrefectural Museum , 54Yamashita-cho, Naka-k Yokohama,Kanagawa 231, Japan 3153Zamami , Zamami-son,Shimajiri-gun, Okinawa 901-34, Japan (ReceivedDecember 7,1993; in revisedform January 11, 1994; accepted February 23, 1994)

Abstract In the Indo-WestPacific bothid flounder Asterorhombus fijiensis, the firstdorsal-fin ray is completelyseparated from the other rays and bears a membranousdistal structure resembling a small fish or crustacean,both in morphologyand coloration. A livespecimen, the fourthknown example of the species,was observed in its naturalhabitat and in an aquarium,and seento repeatedlyvibrate the membranousstructure near its mouth. Although actual attraction of preyspecies was not observed, the firstdorsal-fin ray and membranous structure are interpreted as anillicium and esca, structures used in aggressivemimicry for attracting prey. This is theonly pleuronectiform species known to apparentlylure preywith a modifiedfirst dorsal-fin ray. Thespecies is redescribedin detailand genericcharacte presented.Its distributionisnow known to beFiji Islands, northern Mozambique, Western Australia and southernJapan. Asterorhombus fijiensis and A. intermediusare the only described species in thegenus.

A bothid flounder was observed actively moving Materials and Methods its first dorsal-fin ray, which bore an expanded mem- branous tip, on a coral-sand bottom off the Kerama The live specimen of Asterorhombus fijiensis was a Islands, Okinawa Prefecture. The specimen was male, 109.9mm SL, captured on the north side of collected alive for identification and behavioral ob- Gahi-to Island, Kerama Islands, Okinawa Prefec- servations (Fig. 1). ture, at a depth of 3m on 21 March 1993. After the The first dorsal-fin ray lacked the membrane and specimen was observed and photographed in an pigmentation of the following rays, being entirely aquarium, it was fixed and preserved in formalin, separated from them and resembling a movable il- and deposited in the collection at Izu Oceanic Park licium. Distally the ray had a membranous orange (IOP-3303). flap bearing tiny filaments and a pair of black, eye- The following comparative material was ex- like pigment spots near its proximal end. The struc- amined: ture resembled a small fish or crustacean, being very Asterorhombus fijiensis: BMNH 1879.5.14.89, holotype, similar to the esca (bait) of the Indo-Pacific warty sex unknown, 68.1mm SL, Levuka, Fiji Islands, collected frogfish, Antennarius maculatus (Pietsch and Grobe- by H.M.S. "Challenger"; WAM P28028-013, female, 62.5 mm SL, Rowley Shoals, Cleeke Reef, lagoon edge 2km SE cker, 1978, 1987). An illicium and esca have never of Bedwell Island (17•‹18'S, 119•‹22'E), 1-2m depth, before been reported for a flatfish. August 8, 1983. Asterorhombus intermedius: BSKU 8376, The fish was identified as Asterorhombus fijiensis, male, 122.0mm SL, Mimase, Kochi Pref., July 1, 1958; known previously from three specimens. In this FAKU 17541, female, 103.5mm SL, Miya, Aichi Pref., March 15, 1952; CSIRO CA3606, male, 91.7mm SL, paper, the species is redescribed in detail and generic 20•‹31'S, 116•‹05'E, east of Monte Bello Islands, January characters presented, in addition to observations on 22, 1983; CSIRO CA3826, female, 98.9mm SL, 19•‹40'S, the use and morphology of the illicium and esca. 119•‹01'E, November 18, 1982.

•\ 2 3•\ K. Amaoka, H. Senou & A. Ono

Fig. 1. Photographs of living specimen of Astero- rhombusfijiensis. Top-IOP-3303, male, 109.9 mm SL, from Kerama Islands, Okinawa Pre- fecture;left-close-up of head with lure.

base to the last-ray base. The caudal skeleton and vertebral counts were examined by radiographs. In- stitutional abbreviations follow Leviton et al. (1985), except for IOP (Izu Oceanic Park).

Description

Body ovate, deepest at middle, depth somewhat more than half length of body; dorsal and ventral contours gently arched. Caudal peduncle deep, depth slightly more than 1/4 of body depth. Head rather large, length more than about 1/4 of SL; upper profile rather steep, with a slight notch at dorsal-fin origin. Snout long, length about twice eye diameter; somewhat enlarged at tip and deeply concave in front of interorbital area. Rostral and orbital spines absent. Eyes very small, diameter a little less than Counts and measurements follow those of Hubbs half upper-jaw length; lower eye in advance of upper. and Lagler (1958) with the exception that the pelvic- Interorbital region wide, deeply concave, width fin base lengths were measured from the first-ray slightly less than twice eye diameter. Nostrils on

•\ 2 4•\ Record and Lure, Asterorhombus fijiensis

A

A

B

BFig. 3. Lure of first dorsal-fin ray of Asterorhombus fijiensis. A) Expanded; B) natural condition. Scale bar indicates 5mm.

Dorsal fin originating on blind side, on horizontal line through middle of interorbital space; fin rays 2- 10 increasing in length, subsequently decreasing in length to 25th fin ray, increasing in length to posteri- Fig. 2. A) Gill rakers of first gill arch; B) caudal or 1/3 of body, and decreasing in length to last fin skeleton of Asterorhombusfijiensis. Each scale bar indicates 5mm. ray. First dorsal-fin ray (illicium) completely free from remaining rays, without usual fin-membrane or flaps; distal 1/10 of 1st ray supporting a large, later- ocular side above horizontal line through upper ally compressed leaf-like membrane (esca) (Fig. 3A), margin of lower eye, anterior nostril tubular with a anterior 2/3 of margin of membrane folded post- flap posteriorly, posterior nostril more or less tubu- eroventrally (Fig. 3B); many tiny, compressed fil- lar; nostrils on blind side small, below 2nd dorsal ray, amentous and membranous projections on ventral similar in shape to those on ocular side. margin and lateral surface of esca (Fig. 3). Several Mouth rather large, oblique and gently arched; following dorsal rays with membranes deeply in- maxilla extending almost to below anterior part of cised, i.e. pinniform; free portions of these rays with lower eye; anterior tip of lower jaw projecting slight- many tiny filaments. Anal fin originating on vertical ly beyond tip of upper jaw when mouth closed. Some line along posterior margin of preopercular bone, flaps on ventral margin of posterior half of lower similar in shape and structure to dorsal fin, except for jaw, anterior-and posteriormost larger than others. anterior rays. Pectoral fin on ocular side small, Teeth uniserial on both jaws; teeth on upper jaw subequal to half of head length; 1st ray shortest, 2nd somewhat enlarged anteriorly, becoming smaller, ray longest; fin on blind side more feeble than that on short and close-set posteriorly; teeth on lower jaw ocular side, middle ray longest. Pelvic fins with 6 similar in size and space to anterior teeth on upper rays; fin on ocular side starting at tip of isthmus, jaw. Gill rakers on 1st arch palmate, with 2 to 5 anterior 3 rays pinniform with many tiny flaps on spines on each margin; no gill rakers on upper limb distal portion; fin on blind side starting next to 3rd (Fig. 2A). Scales on ocular side moderate in size, ray of ocular side. Tip of isthmus on vertical line with moderate ctenii; snout tip, both jaws, anterior through anterior margin of lower eye. Caudal fin dorsal-fin ray, and pectoral and pelvic fins naked; round, all rays branched, except for 2 upper-and cycloid scales on blind side. Lateral line curved lowermost rays. Vent opening on blind side, above above pectoral fin on ocular side; length of curved origin of anal fin. Genital papilla on opposite side of portion about 2/3 and height about 1/3 of head vent. length; lateral line absent on blind side. Coloration in formalin.-Ground color on ocular

•\2 5•\ K. Amaoka, H. Senou & A. Ono side whitish-gray, mottled with indistinct darker New Japanese name.-Taikoubou-daruma, mean- ocelli and numerous small, dark spots scattered on ing angler flounder. body; a distinct black spot on lateral line in front of caudal peduncle; median fins with many pale and dark spots. Blind side white, without markings. Habitat and Behavioral Observations Coloration in life (Fig. 1).-Ground color on ocular side light brown, mottled with brownish The specimen was found in clear water at a depth blotches and black spots; a distinct black spot on of 3m on a coral-sand bottom near many small, lateral line in front of caudal peduncle; 7 red spots on scattered reefs. Gobiid fishes (Fusigobius and Gnatho- lateral line, 2 along opercular margin, 1 in front of lepis spp.) were observed near the flatfish. Frag- upper eye, and 1 on middle of lower jaw; a vertical ments of sea-weeds collected by tidal currents were red band on interorbital concavity; a series of paler drifting near the bottom. When the flatfish was first red spots on dorsal, anal, caudal and pelvic fins on seen on the bottom, its entire body was exposed on ocular side. First dorsal ray (illicium) white; lateral the sand. It repeatedly made short (ca. 1cm) swim- side of esca, except for marginal portion, yellowish- ming advances, at the same time bringing the esca red; a pair of tiny black spots at base of esca. near its mouth and vibrating it, before depressing the Distribution.-Fiji Islands (Giinther, 1880; illicium, thus moving the esca back onto the head. Norman, 1931), northern Mozambique (Hensley, The fish repeated such movements of the illicium and 1984, 1986), Bedwell Island, Western Australia and esca many times. When approached closely by a Kerama Islands, Okinawa, Japan. diver, the fish swam rapidly, raising a cloud of sand.

Table 1. Morphometric proportions expressed as percent of SL and counts of Asterorhombus fijiensis

o, ocular side; b, blind side.

•\2 6•\ Record and Lure, Asterorhornbus fijiensis

It then stopped and swam backward for about 15 cm causing the dorsal surface to be thicker than the into the sand, becoming completely hidden, although ventral membranous area (Fig. 3B). Many small, its body outline was still slightly visible. Such behav- compressed filaments are located along the ventral ior is very similar to that of Bothus pantherinus and margin and sides, appearing to mimic the pectoral B. mancus, two of the more common bothids living and pelvic fins of a small fish or the appendages of a near coral reefs. small crustacean. The distal end of the esca is somewhat tapered, resembling the tail of a crusta- cean or fish. The coloration of the esca, yellowish- Discussion red dorsally and becoming much paler ventrally, follows the general pattern of coloration in marine Comparison of the present specimen with the animals. Spots, resembling a pair of dark eyespots, holotype of Asterorhombus fijiensis (BMNH are present on the proximal portion. 1879.5.14.89; Norman, 1931) indicated no substan- Although the specimen was at no time observed to tial differences, except for the interorbital width actually attract prey in its natural habitat or in the (Table 1). Like most bothids, this species probably aquarium, judging from its movements, and the mor- shows positive allometric growth of the interorbital phology and coloration of the esca, there seems to be region. no doubt that the species uses the latter structure in Norman (1931, 1934) suggested that the species aggressive mimicry. resembled Arnoglossus intermedius (=Asterorhom- Among cases of aggressive mimicry utilizing a lure bus intermedius, see Amaoka, 1969:111) in the to attract prey, the evolutionary origins of the lures peculiar form of the gill rakers. Hensley (1984, are very diverse (Randall and Kuiter, 1989), the 1986) moved the species from Engyprosopon to Astero- following examples having been reported: dorsal fin rhombus, but gave no reason. Our examination of A. of the scorpaenid, Iracundus signifer (Shallenberger fijiensis and A. intermedius, has enabled a definition and Madden, 1973), tongue of the ophichthid, Gle- of the genus based on the following characters: no noglossa wassi (McCosker, 1982), first dorsal-fin ray noticeable sexual dimorphism in interorbital width, of many families of lophiiform fishes (Norman, fins, or rostral and orbital spines; palmate gill rakers 1963:40; Pietsch and Grobecker, 1978, 1987), a flap (Fig. 2A); first dorsal-fin ray separated from other of skin in front of the mouth of the uranoscopid, fin rays; no sexual differences in body coloration on Uranoscopus oligolepis (Norman, 1963:95), and pec- blind side; and parhypural and hypural plates with toral fin of various flatfishes (Randall, pers. comm. in deep clefts (Fig. 2B). Shallenberger and Madden, 1973). However, as far Following the species initial report as "Rhomboid- as we know, a lure formed from a modified first ichthys sp. (?)" by &anther (1880), based on one dorsal-fin ray is known only in the anglerfishes and specimen from near the Fiji Islands, further exam- A. fijiensis. ples were unknown until Hensley (1984, 1986) re- ported a single specimen from northern Mozam- bique. During this study, a specimen from Western Acknowledgments Australia was also identified as A. fijiensis. Thus, the specimen discussed in this paper is the fourth known Many thanks are due to Dr. Dannie A. Hensley, example of the species and the first record from the University of Puerto Rico, for his critical review of Western Pacific and Japan. However, A. fijiensis the manuscript, and Dr. Theodore W. Pietsch, Uni- probably has a much wider distribution in the tropi- versity of Washington, for his helpful comments on cal and subtropical waters of the Indian and Pacific the lure. We thank Drs. James Chambers, British oceans. Because it is a relatively small species, living Museum (Natural History), Gerald R. Allen, West- in sandy areas between and around coral reefs, it is ern Australia Museum, Peter R. Last, CSIRO Divi- likely that any future collections will be made by sion of Fisheries Research, Tamotsu Iwai, Kyoto divers, rather than by trawls or seines. University, and Osamu Okamura, Kochi University, The esca of A. fijiensis is a compressed, membra- for lending us specimens for comparison, and Mr. nous, leaflike structure, resembling a small fish or Eiji Mihara, Mr. Gen Yasuda and Mr. Masahito crustacean. In its normal state (i.e. not artificially Arai, Hokkaido University, for making radio- unfolded) the dorsal portion of the esca is folded, graphs.

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Lakes region. Bull. Cranbrook Inst. Sci., (26). xi+2 13 沖 縄 県 慶 良 間 諸 島嘉 比 島北 側,水 深3mの サ ン ゴ砂 底 で背 鰭 p p. 第1軟 条 を 活 発 に 動 か し,口 に 引 き寄 せ た り,離 した り して い る Leviton,A.E., R.H. Gibbs, Jr., E. Heal and C.E. Dawso n . ダル マ ガ レイ 科 魚 類 が 発 見 さ れ,捕 獲 さ れ た.こ の 個 体 は フ ィ 1985. Standards in herpetologyand ichthyology:Part 1 . ジー諸 島,モ ザ ンビ ー ク北 部,西 オ ー ス トラ リア か ら知 られ て い Standard symboliccodes for institutionalresource coll e c - た タ イ コ ウ ボ ウ ダル マ(新 称)Asterorhombus fijiensisに査 定 され tions in herpetologyand ichthyology. Copeia,1985:80 2 - た.こ の個 体 は西 部 太平 洋 か らの初 めて の 記 録 で あ り,本 種 の4 832. 番 目 の標 本 で あ る.本 個体 は詳 し く再 記 載 され た.本 種 の 背 鰭 第 McCosker,J.E. 1982. A new genus and two new speciesof 1軟 条 は他 の鰭 条 の よ うな鰭 膜 や 色 素 を 欠 き,完 全 に他 の もの か ら分 離 して い た.こ の軟 条 は 先 端 部 に小 魚 ま た は小 型 の 甲 殻 類 remarkable Pacific worm eels (Ophichthidae,subfami ly に似 た オ レ ン ジ色 の 膜 状 の 皮 弁 を持 ち,皮 弁 の基 部 近 くに 眼 の Myrophinae). Proc. Calif. Acad. Sci., 43:59-6 6. よ うな1対 の小 黒 斑 及 び胸 鰭 ・腹 鰭 また は遊 泳 肢 の よ うに 見 え Norman, J.R. 1931. Notes on flatfishes(Heterosomata). I . る多 くの 小 さ い糸 状 物 を備 え て い た.誘 引突 起(イ リシ ウ ム)と Notes on flatfishes of the Bothidae in the Britis h 擬 餌 状 体(エ スカ)を 持 った 攻 撃 擬態 を す る カ レイ 目魚 類 はい ま Museum, with descriptionsof three new species. An n . まで に報 告 さ れ た こ と は な い.本 種 の 帰 属 に つ い て,こ の 種 は両 Mag. Nat. Hist., Ser. 10, 8:507-510 . 眼 間 隔,吻 棘,眼 棘 お よび 鰭 に 二次 性 徴 を発 現 しな い こ と,鰓 杷 Norman, J.R. 1934. A systematic monograph of th e は手 の ひ ら状 で あ る こ と,背 鰭 第1軟 条 は他 の鰭 条 か ら分 離 す flatfishes(Heterosomata). 1. Psettodidae, Bothidae,P l e - る こ と,無 眼 側 の 体色 に二 次 性 徴 が 発 現 しな い こと,下 尾 骨 と準 uronectidae. Brit. Mus., London. viii+459pp. 下 尾 骨 が 分 枝 す る こ とな どの 特 徴 に よ って,セ イ テ ン ビラ メA. intermediusと 共 に セ イ テ ン ビラ メ属 を構 成 す る と考 え るの が 妥 Norman, J.R. 1963. A history of fishes,2nd ed. by P. H. Greenwood, Ernest Benn Limited, London. xxxi+3 9 8 当 で あ る. pp. Pietsch, T.W. and D.B. Grobecker. 1978. The complea t (尼 岡:〒041函 館 市 港 町3-1-1北 海 道 大 学 水 産 学 部 水 angler: Aggressivemimicry in an antennariid anglerfish . 産 動 物 学 講 座;瀬 能:〒231横 浜 市 中 区 山 下 町54神 奈 Science,201:369-370. 川 県 立 博 物 館;小 野: Pietsch, T.W. and D.B. Grobecker. 1987. Frogfishesof ) the world. Systematics,zoogeography, and behaviora l

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