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Congrid Leptocephali in Australasian Waters with Descriptions of Conger wilsoni (Bl. and Schn.) and C. verreauxi Kaup.

L. Ariosoma anago (Temminck and Schlegel, 1842)

L. Ariosoma anago (Temminck and Schlegel, 1842)

1842. Conger anago Temminck and Schlegel, Fauna Japonica, p. 259, p1. 113, fig. 1.
For detailed synonymy see Asano, 1962, pp. 72–73.

Material Examined: Centre d'Océanographie de l'Institut Français d'Océanie Collection (32 specimens): 60.7mm total length, IFO Station D5, 18° 32′ S, 159° 50′ E, 14/5/60 (0820hrs), S½mO (0.5 metre net, No. 2 mesh, oblique tow), 0–300m; 90.5, St A 57–3–3 (8), 22° 37′ S, 166° 20′ E, 6/3/57 (1930 hrs), S½mH, ca. 10m; 117.9, St P58–3–3–4, 21° 41′ S, 166° 15′ E, 31/3/58 (2200hrs), S½mH, ca. 15m; 119.1, St D24, 16° 13.5′ S, 162° 47′ E, 25/5/60 (2329hrs), S½mO, 0–300m; 119.5, 124.3, 135.2, 140.5, 168.8, 179.2, 181.6, St S.2, 20° 10′ S, 163° 27′ E, 7/6/62, MWT5, H, ca. 95m; 129.5, 169.5, St S.l, 21° 45′ S, 165° 10′ E, 6/6/62, MWT5, H, ca. 120m; 142.2, 188.5, St S.11, 21° 31′ S, 164° 48′ E, 25/6/62, MWT5, H, ca. 95m; 145.1, 159.0, St S.3, 18° 10′ S, 162° 00′ E, 8/6/62, MWT5, H, ca. 95m; 151.0, St A57–7–2, 23° 27′ S, 162° 40′ E, 6/7/57 (1800hrs), S½mH, ca. 20m; 160.4, St D8, 17° 07′ S, 157° 47′ E, 15/5/60 (2003hrs), S½mO, 0–300m; 162.0, 190.7, 236.3, St S.10, 17° 40′ S, 162° 25′ E, 22/6/62, MWT5, H, ca. 95m; 248.1, 296.0, and two specimens in poor condition, St 57–4, south coast of Lifu (Loyalty Islands), 22/7/57, stomach of skipjack, Katswonus pelamis; 279.1, 289.5, St LL 57–3–8, 22° 35′ S, 166° 08′ E, 9/7/57 stomach of lancet fish, Alepisaurus ferox; 314.0, St G 23, 22° 07′ S, 165° 04′ E, 22/3/62, S½mO (1.0m net, No. 2 mesh, oblique tow), ca. 167m, sample 23; one specimen in poor condition St LL 61–5, 22° 54′ S, 164° 38′ E, 5/7/61, stomach of striped marlin, Makaira audax; two specimens in poor condition, St G LL 10, 20° 55′ S, 163° 18′ E, 21/3/62, stomach of lancet fish, Alepisaurus ferox.

Western Australian Museum Collection (1 specimen): 167.9, Accession No. P5241, Lancelin, 45 miles west of West End, Rottnest Island, Western Australia, 11/4/62 (0230hrs), larval net, 37m.

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Description: 33 specimens, total lengths 60.7mm–314rnm, myomeres 157–172, maximum dorsal rays 108, anal rays 91. Description made from an almost full-grown specimen, IFO Station S.11 (measurements in mm): total length 188.5, head 5.0, snout 1.8, eye 1.2, cleft of mouth 2.3, postorbital 2.3, pectoral 0.8, snout-vent 184.3, predorsal 185.0, depth just before eye 2.3, at pectoral origin 4.3, at midpoint between pectoral and vent 12.4, at vent 2.9. Dorsal rays 64, anal rays 53, caudal rays 3 + 3. Teeth 1 + IV + 6 over 1 + IV + 6 Myomeres 150 + 10 = 160. 1st vertical blood vessel at myomere 11, last at 81. Anterior margin of gall bladder at myomere 27.

Body extremely elongate but not filamentous, much compressed, except along head, maximum depth about 16 times in total, tapering equally in front of, and behind midpoint of body. Head extremely short, about 38 in total length, indented at the throat; snout conical, 2.8 in head, its dorsal profile straight; nasal organ large, close in front of eye, nares distinct; eye small, about four times in head, round; cleft of mouth oblique, extending to below middle of pupil; teeth broad-based, relatively powerful; an anterior grasping tooth on the anterior tip of snout followed by four large teeth and six much smaller teeth; those on lower jaw similar in size and distribution. Pectoral fin short, about 2.5 in postorbital or equal to horizontal diameter of eye; dorsal and anal fins very short, restricted to posterior tip of body, dorsal origin very close to level of vent, caudal with well-developed hypurals and fin-rays.

Pigmentation in preservative as follows:—below midlateral line on each myoseptum from about the tenth segment to the tail tip an oblique line of minute, compact, elongate, somatic chromatophores, each arranged anteroposteriorly; these pigment spots are few in number anteriorly but increase to about 15–20 (in full-grown specimens of 250mm) in the middle of the body length and finally decrease to about four or five on each myoseptum posterior to the level of the vent; a series of small, diffuse, somatic chromatophores on the dorsal midline from the 15th segment to the level of the vent, 1–2 per segment but more widely spaced posteriorly; a series of small, diffuse, somatic chromatophores along the ventral midline from the pectoral region to about the midpoint of the body length, about six per segment, the series fading out gradually towards the midpoint; posterior to the gall bladder a paired series of small, compact, splanchnic chromatophores along the dorsal aspect of the intestine to the vent, about 9–10 per segment but much less frequent posteriorly; a spot on the bases of most dorsal and anal rays; chorioid pigment present.

Remarks: In the 45 specimens of Ariosoma anago examined by Asano (1962, p. 73) vertebrae numbered 149–159, a range which is appreciably lower than that of the leptocephali here referred to this species (157–172). However, at the present state of knowledge of the adult species of Ariosoma in the Indo-Pacific I hesitate to separate these leptocephali from A. anago on the basis of this difference.

Only one relatively small specimen, measuring 60.7mm total length, is present in the above collection while the others are all over 90mm and reach 300mm, a very large size for congrid leptocephali. In all specimens the vent is very close to the tip of the caudal region indicating that there are no metamorphosing larvae in the collection. However, some show well-developed fin-rays and ossification of the skull, etc., indicating that they are probably full-grown.