IchthyologicalResearch

©The Ichthyological Society of Japan 2001

Ichthyol Res (2001) 48: 100–103

Larva of Chascanopsetta lugubris lugubris (Bothidae)disgorged by a lancetfish (Alepisaurus sp.)

Atsushi Fukui1 , Reiko Tanaka1,*, and Takakazu Ozawa2

1 Department of Fisheries, School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu 424-8610, Japan(e-mail: afukui@scc.u-tokai.ac.jp)2 Faculty of Fisheries, Kagoshima University, 4-50-20 Shimo-arata, Kagoshima 890-0056, Japan* Present address: Graduate School of Fisheries, Kagoshima University, 4-50-20 Shimo-arata, Kagoshima 890-0056, Japan

Received: April 4, 2000 / Revised: June 27, 2000 / Accepted: July 30, 2000

Key words Chascanopsetta · Bothidae · Larva · Gut contents · Lancetfish

Chascanopsetta lugubris lugubris Alcock of the fam-ily Bothidae occurs on the sea bottom at depths

of 270–595 m in the western Pacific and Indian Ocean(Amaoka and Yamamoto 1984). Bruun (1937), Nielsen(1961), Amaoka (1971), and Ozawa and Fukui (1986)described the larva of this subspecies, which is known toattain 120 mm SL (Amaoka 1971), the largest size knownamong pleuronectoid larvae. Such large larvae are rarelycollected, and their morphological development is notsufficiently understood. Interestingly, gut contents havenot been reported from any bothid larvae inclusive ofthis subspecies.

A large larva of this subspecies, 108mm SL, was dis-gorged on deck by a lancetfish (Alepisaurus sp.) caughtin Tasman Sea. The larva was fresh and excellent in con-dition when it was delivered frozen to the AustralianMuseum, by officers of NSW Fisheries. It containedmany food organisms in its gut. This article describes thelarva and the gut contents.

The measurement methods followed Ozawa andFukui (1986), the clearing and staining techniques thoseof Potthoff (1984), and the institutional abbreviationsthose of Leviton et al. (1985). The gut contents werefound to be a copepod, Scolecithrix danae. The copepodswere slightly damaged; therefore, their body lengthswere estimated as follows. The length of intact part fromthe anterior tip of head to the posterior tip of fourththoracic segment was measured on the specimens fromthe gut and used to calculate the total body length fromthe proportions given by Mori (1964). The metasoma ofall the contents was intact, and its maximum width wasalso measured.

Chascanopsetta lugubris lugubris Alcock(Figs. 1, 2)

Material examined. AMS I. 39460-001, 108 mm in standardlength (SL), February 1999, 37° S, 157° E, Lord Howe Island,disgorged by a lancetfish (Alepisaurus sp.) taken by pelagiclongline fishing.

Identification and description. Abdominal (17) andcaudal vertebrae (39) of the present larva were identicalonly with those of the genus Chascanopsetta (15–18 1 37–44) among 20 bothid genera (Ozawa and Fukui,1986; Moser and Charter, 1996; Fukui, 1997). Numbers ofdorsal- and anal-fin rays, and of vertebrae of the presentlarva (Table 1), agreed only with those of C. lugubrisamong the seven species of this genus (Amaoka andYamamoto, 1984; Amaoka and Parin, 1990; Foroshchuk,1991). One of two subspecies in the genus, C. lugubrisdanae, is limited in the Atlantic (Amaoka andYamamoto, 1984); therefore, the present larva could beidentified as the Indo-Pacific C. lugubris lugubris.

A color photograph of the specimen was taken imme-diately after thawing (Fig. 1). Body highly compressedand moderately slender, depth of body 43.2% of SL.Head 10.3% of SL. Abdominal cavity spacious. Gut andliver broadly protruding beyond the ventral profile ofbody. Origin of anal fin located slightly before one-thirdof body length. Upper jaw 31.8% of HL. Outline of snoutconcave (Fig. 2A). Pterygiophore zones of dorsal andanal fins broad, maximum width 59% and 73% of headlength, respectively. Eyes almost circular, width 15.9% ofhead length. Choroid tissue under eye (Ozawa and Fukui,

Larva of Chascanopsetta lugubris lugubris 101

1986) absent. Right eye shifted slightly anterodorsally.Exposed part of urohyal small (the base of posteriorbasipterygial process broken). Cleithrum curved smoo-thly, without spines. All fin rays, except pectorals, defini-tive. First dorsal-fin ray short; second ray broken, thick atbase. All dorsal (except first and second) and anal-fin rayslonger than head length. First ray of right pelvic fin oppo-site between second and third rays of left pelvic fin. In

adults, it is opposite third ray of left fin (Amaoka, 1969).Pectorals fan-shaped, with 2 rays on left side and 13 rayson right side. Air bladder and gill rakers absent.

Choroid tissue is absent in our specimen, but pre-sent in the 66.8 mm larva described by Ozawa andFukui (1986). Pectoral-fin ray formation is completeddefinitively between 108 mm and 120mm SL (Amaoka,1971).

Table 1. Comparison of meristic counts between larva and adults of Chascanopsetta lugubris lugubris and other species ofChascanopsetta

Species Dorsal- Anal- Vertebrae Distribution Sourcefin rays fin rays

C. lugubris lugubrisLarva 120 83 17 1 39 5 56 Present studyLarvae 112–127 78–88 16–17 1 37–41 5 53–58 Ozawa and Fukui (1986)Adults 115–125 79–86 16–18 1 37–41 5 54–58 Western Pacific Amaoka and Yamamoto (1984)

Indian OceanC. micrognatus

Adults 124–130 93–98 15–17 1 42–44 5 58–60 Kyushu-Palau Ridge Amaoka and Yamamoto (1984)C. prognatha

Adults 124–133 86–93 17–18 1 42–44 5 59–61 Sagami Bay, Okinawa Amaoka and Yamamoto (1984)Trough, Maldive area

C. prorigeraAdults 119–125 85–89 16–17 1 40 5 56–57 Hawaiian waters, Amaoka and Yamamoto (1984)

Emperor SeamountC. crumeralis

Adults 121–122 84–86 17 1 40 5 57 Hawaiian waters Amaoka and Yamamoto (1984)

C. megagnathaAdults 111–118 71–81 16–18 1 36–39 5 52–56 Eastern Pacific Amaoka and Parin (1990)

C. elskiAdults 106–116 80–85 16–17 1 34–39 5 50–56 Saya de Malha Bank Foroshchuk (1991)

C. lugubris danaeAdults 114–120 80–87 16–18 1 37–39 5 54–56 Atlantic Ocean Amaoka and Yamamoto (1984)

Fig. 1. Photograph of larva of Chascanopsettalugubris lugubris, 108mm SL, AMS-I.39460-001,just after the disgorgement by a lancetfish

102 A. Fukui, et al.

First pterygiophore supports first and second dorsal finrays (Fig. 2A). Filamentous process of second neuralspine extending between 15th and 16th pterygiophores.Anterior and posterior part of pterygiophores cartilagi-nous (stained with alcian blue). Terminal half of centrumand hypural 3 1 4 1 5 autogenous (Fig. 2B). Hypural,epural, and parhypural mostly ossified, except distally.Proximal and distal parts of neural and haemal spines ofsecond and third preural centra cartilaginous. Neural andhaemal spines of second preural centrum not supportingcaudal-fin rays. Caudal skeleton of adults of this sub-species (165-mm SL, as C. lugubris [Fujita, 1990]) differsfrom the present larva in the following characters: (1)terminal half of centrum and hypural 3 1 4 1 5 united;(2) neural and haemal spines of second preural centrumsupport caudal-fin rays; and (3) basal part of neural spineof second preural centrum bifurcate.

Melanophores.—Discontinuous rows of punctate mel-anophores present as follows: along interspine bases ofdorsal and anal fins (both sides) and lateral midline (inmuscle); along dorsal margin of body between 10th and90th dorsal-fin rays and ventral margin of body between

3rd and 43rd anal-fin rays. Six punctate melanophorespresent on posterior wall of abdominal cavity, and sev-eral minute ones basally on second dorsal-fin ray. Themelanophore pattern of the 66.8 mm SL specimen il-lustrated by Ozawa and Fukui (1986) is similar to thepresent larva except that melanophores are lacking ondorsal and ventral body margins.

Xanthophores.—Six masses present along pterygio-phore zone of dorsal fin and three along pterygiophorezone of anal fin. A mass present around caudal peduncleexpanding into dorsal and anal pterygiophore zones. Anarrow band from base of second dorsal-fin ray toopercle margin. Discontinuous row along lateral midline.This pattern is identical to that of the larva 78mm SL (asC. lugubris) illustrated by Bruun (1937).

Gut and its contents.—Gut slender, length from pyloricceca to anus 155 mm, and outside diameter 1.1–1.5 mm.Gut contents visible externally, as a brilliant orange lon-gitudinal line within entire gut. Composed of 66 individu-als of the copepod Scolecithrix danae, which were slightlydamaged and shrunken due to absorption of body fluid.Averaged estimated body length was 2.3mm (range, 1.8–

Fig. 2. Skeletal structures of Chascanopsetta lugubris lugubris, 108 mm SL, AMS-I.39460-001 (specimen cleared and stained).A Lateral view of anteriormost dorsal fin pterygiophores and head; B lateral view of caudal skeleton. E, epural; EPO, epiotic; FP,filamentous process of second neural spine; H, hypural; HPU, haemal spine of preural centrum; NES, neural spine; NPU, neuralspine of preural centrum; OPE, opercle; PH, parhypural; PP, pterygiophore; PU, preural centrum; THC, terminal half centrum.Shaded areas indicate cartilage stained with alcian blue. Bars, 1 mm

Larva of Chascanopsetta lugubris lugubris 103

2.7mm; n 5 46); average maximum width was 0.7 mm(0.6–0.9 m; n 5 50).

Remarks. The lancetfish (Alepisaurus sp.) that dis-gorged the present larva on deck was not identifiedto species by the fisherman nor measured nor retained.The present larva provides information on morphologi-cal development of C. lugubris lugubris at a stage be-tween 66.8 mm SL (Ozawa and Fukui, 1986) and 120mmSL (Amaoka, 1971).

Bothid larvae characteristically have a small mouthand a slender, coiled, thin gut. No gut contents have beenreported previously. Ozawa and Fukui (1986) studied theearly ontogeny of bothids and examined, externally,gut contents of about 4000 larvae (2.88–66.8 mm SL) butfailed to find any gut contents. Most of the copepods inthe gut of the present specimen did not contain bodyfluids in their carapaces, indicating that they weredigested. Apparently, bothid larvae caught in net towsevacuate their guts during the course of the tow. Perhapsthis did not occur in our specimen because it was killedinstantly by the predator. Examinations of gut contentsof other larvae taken from Alepisaurus stomachs couldprovide informations on feeding behavior of larvae thatis not available from net tow specimens.

Acknowledgments We are sincerely grateful to Dr. Jeffrey M.Leis, Australian Museum, Sydney (AMS), for his valuable ad-vice and critical reading of the manuscript. Grateful thanksare also given to Mr. Carl Bento, AMS, for taking the photo-graph of the bothid larva, and Mr. Mark McGrouther, AMS, forloaning its larva; and to Dr. Itsuro Uotani and Mr. TakeshiMizushima, Tokai University, for their valuable suggestions andhelp.

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