L. Ariosoma mauritianum (Pappenheim, 1914)

Material Examined: Centre d'Océanographie de l'Institut Français d'Océanie Collection (19 specimens): 43.7mm total length, IFO Station D15b, 9° 50′ S, 159° 20′ E, 22/5/60 (0219hrs), S½mO (0.5 metre net, No. 2 mesh, oblique tow), 0–300m; 53.6, 163.7, St S.6, 11° 51′ S, 159° 13′ E, 10/6/62, MWT5, H, ca. 95m; 56.0, St S.5, 13° 30′ S, 162° 05′ E, 10/6/62, MWT5, H, ca. 95m; 57.5, 89.8, 110.0, St P As 7 Hel 2, 23° 28′ S, 159° 23′ E, 8/5/58 (2015hrs), HeO (Heligoland larval fish net, oblique), ca. 100m; 81.2, St 7–3, 22° 35′ S, 166° 16′ E, 17/7/62, MWT5, H, ca. 35m; 93.9, St D19, 11° 19′ S, 162° 43′ E, 23/5/60 (2027hrs), S½mO, 0–300m; 98.6, St Foa 1m, 21° 21′ S, 164° 15′ E, 11/1/62, S1mO (1.0m net, No. 2 mesh, oblique), ca. 167m, sample 4; 126.6, 210.0, 269.0, 278.0, St LL 57–3–8, 22° 35′ S, 166° 08′ E, 9/7/57, stomach of lancet fish, Alepisaurus ferox; 145.1, St LL 57–6–3, 22° 50′ S, 165° 36′ E, 7/12/57, stomach of lancet fish, Alepisaurus ferox; 151.2, St Ep7b, 18° 23′ S, 159° 47′ E, 16/9/60 (0209hrs), S½mO, 0–300m; 173.0, St Foa MWT, 18° 35′ S, 159° 47′ E, 13/1/62, MWT3, H, ca. 100m, sample 4; ca. 181, St Foa MWT, 22° 20′ S, 165° 42′ E, 10/1/62, MWT3, H, ca. 100m, sample 1; 198.0, St LL 59–1–3, 22° 45′ S, 162° 44′ E, 30/1/59, stomach of lancet fish, Alepisaurus ferox.

C.S.I.R.O. Division of Fisheries and Oceanography (Cronulla) Collection (14 specimens): 11.8, 16.0, 16.8, Warreen Station 32/38, 24° 29.5′ S, 153° 26.5′ E, 20/9/38, N100, H, surface, 30 mins; 12.7, 19.4, 26.1, St 32/38, 24° 29.5′ S, 153° 26.5′ E, 20/9/38, N70, H, 25m, 30mins; 35.0, Tasman Sea, 3/4/49, N70, surface; 49.0, Warreen St 30/48, 32° 03′ S, 113° 30′ E, 24/8/48, N70, H, surface, 15mins; 60.8, St 205/39, 34° 03′ S, 151° 11.5′ E, 4/8/39, N70, O, 0–25m; 76.2, St 26/40, 32° 34′ S, 152° 55′ E, 20/4/40, N100, O, 0–200m; 86.4, St 129/39, 32° 34′ S, 152° 55′ E, 3/5/39, N100, H, 100m, 60mins; 100.6, St 206/39, 33° 56′ S, 151° 19′ E, 4/8/39, N200, H, surface; 117.4, St 37/38, 28° 37′ S, 153° 54′ E, 22/9/38, N70, H, 100m, 30mins; 230.3, St 3/49, 32° 03′ S, 114° 53.5′ E, 7/4/49, N70, H, surface, 10mins.

Australian Museum Collection (1 specimen): 102.1, Aust. Mus. regd. No. IA.3815, Dana Station 3663, haul 9, Tasman Sea, 33° 33′ S, 154° 04′ E, 23/2/29, ca. 50m.

Western Australian Museum Collection (47 specimens): 11.1, Accession No. P5229, Lancelin, 16 miles west of West End, Rottnest Island, Western Australia, 4/4/62 (0030hrs), larval net, 37 metres; 14.4, P5287, 34mls, 3/7/62 (0300– 0100hrs), In, 37m; 17.4, P5291, 44mls, 3/7/62 (0300–0330hrs), N70, surface; 19.1, P5308, 44mls, 3/7/62 (0300–0330hrs), N70, surface; 59.4, P5169, 50mls, 11/9/61 (2345–0015hrs), In, 110m; 70.5, P5537, 45mls, 10/10/62 (0150hrs), In, 37m; 87.3, P5553, 44mls, 7/11/62 (0230hrs), N70, surface; 88.5, P5554, 43mls, 7/11/62, In, 110m; 91.4, 137.3, P5556, 25mls, 13/11/62 (0100hrs), In, 37m; 92.2, P5541, 43mls, 10/10/62 (0330hrs), In, 110m; 96.3, 100.9, P5552, 45mls, 7/11/62 (0140hrs), In, 37m; 99.6, P5539, 44mls, 10/10/62 (0239hrs), In, 37m; 104.4, P5559, 40mls, 15/11/62 (0320hrs), In, 110m; 113.6, 133.5, P5555, 42mls, 7/11/62 (0440hrs), In, 37m; 118.0, P5550, 43mls, 7/11/62 (0010hrs), In, 37m; 121.2, P5551, 44mls, 7/11/62 (0100hrs), In, 37m; 121.3, P5244, 20mls, 4/4/62 (0430hrs), N70, surface; 137.1, 184.0, P5150, 43mls, 7/3/62 (0115–0145hrs), In, 37m; 138.7, P5154, 40mls, 7/3/62 (0330–0400hrs), In, 37m; 139.5, 165.6, 168.8, 176.9, 177.5, P5156, 43mls, 12/2/62 (0000–0030hrs), In, 37m; 139.8, P5178, 40mls, Feb./Mar., 1962, In, 37m; 145.0, 182.5, P5177, 42mls, 12/2/62 page 11

Text-fig. 3.—Fig. A, distribution of 34 specimens of L. Ariosoma mauritianum in the southwest Pacific. fig. B, number of myomeres in (a) L. Ariosoma anago (32 specimens), (b) L. Ariosoma (80 specimens), (C) L. Ariosoma scheelei (66 specimens).

(0100–0130hrs), In, 37m; 146.9, P5176, 39mls, 12/2/62 (0315–0345hrs), In, 110m; 150.1, 163.0, 167.3, 168.6, P5155, 40mls, 13/2/62 (0230–0300hrs), In, 37m; 171.2, 178.5, 190.5, P5151, 41mls, 12/2/62 (0145–0215hrs), In, 37m; 178.3, P5296, 38mls, 7/3/62, In, 37m; 190.1, P5226, 40mls, 30/3/62 (0230hrs), In, 37m; 193.1, 204.3, P5166, 38mls, 12/2/62 (0415–0445hrs), In, 37m; 194.5, P5183, Umitaka Maru, 13° 45′ N, 115° 12′ E, 8/11/62, In; 198.0, P5247, Lancelin, 43mls, 30/3/62, In, 37m.

Description: 81 specimens: total lengths 11.1mm–278.0mm, myomeres 134–153, maximum number of dorsal fin-rays observed 120, anal 111. Description made from a half-grown specimen, Western Australian Museum Ace. No. P5553 (measurements in mm): total length 87.3, head 3.6, snout 1.5, eye 0.8, cleft of mouth 1.9, postorbital 1.5, pectoral 0.8, page 12snout-vent 82.1, predorsal 82.9, depth just before eye 1.8, at pectoral origin 2.5, at midpoint between pectoral and vent 8.4, at vent 2.0. Dorsal rays ca. 45, anal rays 40, caudal rays 5 + 4. Teeth Myomeres 128 + 11 = 139. 1st vertical blood vessel at myomere 17, last at 75. Anterior margin of gall bladder at myomere 27.

Body conspicuously elongate, much compressed except along head, maximum depth contained about 10 times in total length, tapering equally in front of, and behind, the midpoint of body. Head very short, about 24 in total, with the throat indented; snout conical, about 2.5 in head, its dorsal profile slightly concave; nasal organ large, close in front of eye, its dorsal margin with a ventral extension midway along its length indicating approaching separation of the nares; eye small, 4.5 in head, round; cleft of mouth oblique, reaching to below middle of pupil; teeth rather broad-based, acute; anterior grasping tooth on the extreme tip of snout followed by a series of four large teeth and then by another series of seven smaller teeth; those on lower jaw similar. Pectoral fin short, about 2.0 in postorbital, delicate, rounded; dorsal and anal fin very short, restricted to posterior tip of body, dorsal origin close to level of vent, caudal with well-developed hypurals and fin-rays.

Pigmentation in preservative as follows:—below the midlateral level on each myoseptum from the seventh to the last an oblique line of minute, compact, elongate, somatic chromatophores, each arranged anteroposteriorly; these pigment spots are few in number anteriorly and are more numerous (usually about 12 in specimens of about 100mm total length but up to 20 in larvae of about 180mm) in the middle of the body length but decrease again in number until posterior to the level of the vent they number about four on each myoseptum; from about segment 20 to level of vent an unpaired series of small, diffuse, somatic chromatophores, 1–2 to each segment, on the dorsal midline; from the pectoral region to about halfway along the body length an unpaired series of small, diffuse, somatic chromatophores, about 5–6 to each segment, on the ventral midline, this series becoming less regular and fading out beyond the midpoint; posterior to the gall bladder a paired series of small, compact, splanchnic chromatophores above the intestine, about 6–9 per segment, through to the vent, although these are much less regular along the posterior part of the intestine; a few scattered chromatophores on the dorsal and anal bases; chorioid pigment present.

Remarks: The specimens described above have the larval pigmentation, round eye, short dorsal and anal fins and subterminal vent established for leptocephali of the genus Ariosoma. They agree well with Leptocephalus mauritianus Pappenheim, 1914, from Mauritius which has 140–145 myomeres (that is, in the middle of the range of 134–153 for the present material). Ariosoma howensis (McCulloch and Waite, 1916) from Lord Howe Island, of which the present author has examined one specimen, has about 154 vertebrae and is included here as a provisional synonym of L. Ariosoma Mauritianum.

Geographical Range and Location of the Spawning Areas (Text-fig. 3, A).

The present leptocephalus is now known from the Solomons, through New Caledonia and as far south as Sydney, but also occurs abundantly on the west Australian coast; a few specimens have been recorded from Mauritius and the Red Sea. Smallest specimens were taken off Sydney and Rottnest Island, Western Australia and suggest that spawning takes place in these areas. The leptocephali of this species collected in the neighbourhood of the western spawning area during 1962 fall into three well-defined groups, as indicated in text-fig. 4. The smallest larvae, below 20mm (a), were trawled in May-June and indicate a spawning in March-April; half-grown larvae, averaging 100mm (b), appeared in trawls made during October-November. Early in the year, in February-March, 1962, only large, full-grown larvae of about 150mm–200mm were collected and these are clearly larvae from the March-April spawning of the previous year, 1961. The larval life of Ariosoma mauritianum is therefore at least one year but is probably not much more than this, especially since most of the larger larvae appear to be close to metamorphosis.

The species is not so abundant as L. Ariosoma scheelei in the New Caledonia area and the smallest specimen from this region is 43.7mm in total length suggesting that spawning probably does not occur here. Ancona (1928, p. 37) records a 117mm specimen of L. Ariosoma mauritianum from the Red Sea, and together with the Mauritius examples, a third spawning area, off east Africa, is suggested.

Text-fig. 4.—Lengths of 46 leptocephali of Ariosoma mauritianum collected off Western Australia during 1962; (a) very young larvae from the March-April spawning, (b) half-grown larvae, (c) full-grown larvae from the March-April spawning of 1961.