Congrid Leptocephali in Australasian Waters with Descriptions of Conger wilsoni (Bl. and Schn.) and C. verreauxi Kaup.
L. Ariosoma scheelei (Strömman, 1896), Text-fig. 1, A-I
L. Ariosoma scheelei (Strömman, 1896), Text-fig. 1, A-I
|1896.||Leptocephalus scheelei Stromman (partim), Lept. Univ. Mus. Upsala, pp.21–24, p1. 1, figs. 6–7.|
|1913.||(non) L. taenia Lesson. Weber, Siboga Exped., 57: 67.|
|1913.||L. Indicus Weber, Siboga Exped., 57: 74.|
|1916.||L. Indicus Weber. Weber and De Beaufort, Fish. indo-aust. archipel., 3:99, fig. 195.|
|1916.||(non) L. taenia Lesson. Weber and De Beaufort, Fish. indo-aust. archipel., 3: 404–406, figs. 204–207.|
|1928.||(non) Ophisoma anago (Temm. and Schleg.). Ancona, Mem. R. Com. talassogr. ital., 146: 13–14, p1. 1, fig. 1.|
|1928.||(non) L. Ophisomatis anagoi (Temm. and Schleg.). A Ncona, Mem. R. Com. talassogr. ital., 146: 17–27, p1. 2, figs. 1–4a.|
|1934.||?Larva I. Deraniyagala, Ceylon J. Sci., B19 (1): 91–92, fig. 1.page 4|
|1936.||L. Scheelei Strömman. Bertin, Bull. Inst. oceanogr. Monaco, 694: 3–5, fig. 4.|
|1939.||?Ariosoma nigrimanus Norman, Sci. Rep. John Murray Exped., 7 (1): 39–40, fig. 12.|
|1949.||(non) Congrellus anago (Temm. and Schleg.). Gopinath, Rec. Ind. Mus., 47 (1): 93, p1. 10, fig. 4, tex-fig. 1c.|
|1956.||(non) L. Ophisomatis anagoi (Temm. and Schleg.). Fowler, Fish. Red Sea Sth. Arabia. I, p. 114.|
Text-fig. 1.—L. Ariosoma scheelei (strömman, 1986). Figs. A-D 105mm total length, IFO Station 7–2: Fig. A, lateral view; Fig. B, lateral view of head; Fig. C, tip of caudal region; Fig. d, distribution of pigment at level of gall bladder. Figs. E-F, 15.1mm total length, IFO Station 7–5: Fig. E, lateral view; Fig. F, teeth. Figs. G-I, 31.2mm total length, IFO Station S.3: Fig. G, lateral view; Fig. H, teeth; Fig. I, tip of caudal region.
Material Examined: Centre d'Océanographie de l'Institut Franç ais d'Océanie Collection (64 Specimens): 15.1mm total length, IFO Station 7–5, 22° 35′ S, 166° 16′ E, 26/7/62, MWT5 (5ft Isaacs-Kidd midwater trawl) horizontal tow, ca. 120 metres; 16.2, 123.5, St S.1, 21° 45′ S, 165° 10′ E, 6/6/62, MWT5, H, ca. 120m; 20.0, 27.2, 57.8, 71.2, 71.5, 71.8, 73.3, 77.2, 78.1, 79.8, 111.0, 115.3, 128.3, 128.4, St S.2, 20° 10′ S, 163° 27′ E, 7/6/62, MWT5, H, ca. 95m; 23.2, 25.3, 26.1, 30.0, 31.2, 71.1, 105.2, St S.3, 18° 10′ S, 162° 00′ E, 8/6/62, MWT5, H, ca. 95m; 25.6, 36.1, 37.8, 40.7, 73.7, St 7–4, 22° 35′ S, 166° 16′ E, 17/7/62, MWT5, H, ca. 35m; 30.5, MWT 3 I, 10 miles west of Bulari Pass, New Caledonia, 1/8/61, MWT3, H, ca. 40m, sample 6, 42.4, MWT3, H, ca. 17m, sample 1, 142.5, MWT3, H, ca. 83m, sample 3; 34.8, 61.5, St P57–5–1, 20° 06′ S, 168° 40′ E, 9/9/57 (0045hrs), S½mH (0.5m net, No. 2 mesh, horizontal tow), ca. 20m; 37.4, St 56–4–19, 14° 15′ S, 172° 14′ E, 21/10/56 (0001hrs), S½mH, ca. 50m; 37.6, St 56–5–3, 15° 45′ S, 166° 27′ E, 31/10/56 (2248hrs), S½mO, ca. 150m; 40.5, 51.2, 85.0, 99.0, St S.7, 10° 48′ S, 159° 00′ E, 12/6/62, MWT5, H, ca. 95m; 40.9, St MWT 2, 10 miles west of Bulari Pass, 30/11/61, MWT3, H, ca. 67m, sample 2; 41.9, St S.5, 13° 30′ S, 162° 05′ E, 10/6/62, MWT5, H, ca. 95m; 44.0, 45.8, St 7–1, 22° 35′ S, 166° 16′ E, 17/7/62, MWT5, H, ca. 70m; 45.2, St P58–3–3–6, 22° 41′ S, 166° 15′ E, 11/4/58 (0500hrs), S½mO, ca. 30m; 53.2, 62.3, St 56–3–4, 17° 52′ S, 168° 08′ E, 17/5/56 (0250hrs), S½mH, ca. 5m; 68.0, 77.5, St D10, 14° 50′ S, 157° 52.5′ E, 16/5/60 (2003hrs), S½mO, 0–300m; 75.9, St D10b, 14° 13′ S, 157° 55′ E, 17/5/60 (0214hrs), S½mO, 0–300m; 76.1, St D14, 10° 16′ S, 158° 37.5′ E, 18/5/60 (2012hrs), S½mO, 0–300m; 78.0, St D9b, 15° 21′ S, 157° 57′ E, 16/5/60 (1415hrs), S½mO, 0–300m; 91.8, St D12, 12° 39′ S, 157° 59′ E, 17/5/60 (2003hrs), S½mO, 0–300m; 96.5, 105.0, 131.2, St 7–6, 22° 35′ S, 166° 16′ E, 26/7/62, MWT5, H, ca. 50m; 105.0, St 7–2, 22° 35′ S, 166° 16′ E, 17/7/62, MWT5, H, ca. 70m; 106.9, St 7–8, 22° 35′ S, 166° 16′ E, 26/7/62, MWT5, H, ca. 20m; 112.9, ca. 120 (damaged), 121.1, St S.10, 17° 40′ S, 162° 25′ E, 22/6/62, MWT5, H, ca. 95m; 122.7, St 7–7, 22° 35′ S, 166° 16′ E, 26/7/62, MWT5, H, ca. 160m; 126.3, St LL57–5–4, 21° 33′ S, 166° 31′ E, 11/9/57, stomach of lancet fish, Alepisaurus ferox; 154.8, St S.11, 21° 31′ S, 164° 48′ E, 25/6/62, MWT5, H, ca. 95m.
Australian Museum Collection (2 Specimens): 119.2, Aust. Mus. regd. no. IB.3999, Collaroy, New South Wales, 17/9/58; 131.0, Aust. Mus. regd. no. IB.2954, Hawk's Nest Beach, New South Wales.
Western Australian Museum Collection (1 Specimen): 85.8, Accession No. P5172, 49 miles west of West End, Rottnest Island, Western Australia, 1/8/61 (0330–0430hrs), larval net, 110m.
Description: 67 specimens: total lengths 15.1mm-154.8mm, myomeres 110–119, dorsal and anal fin-rays greatest in number in the longest specimen, 102 and 106 respectively. Description made from a full-grown specimen, IFO St 7–2 (measurements in mm): total length 105.0, head 3.3, snout 1.2, eye 0.8, cleft of mouth 1.5, postorbital 1.5, pectoral 0.9, snout-vent 100.0, predorsal ca. 98.5, depth just before eye 1.7, at pectoral origin 2.7, at midpoint between pectoral and vent 12.3, at vent 4.3. Branchiostegal and pectoral rays not developed, dorsal rays 77, anal rays 67, caudal rays 3 + 3 + 1. Teeth Myomeres 105 + 10 = 115. a–d = ca. 2. 1st vertical blood vessel at myomere 18, last at 58. Anterior margin of gall bladder at myomere 22.page 6
Body moderately elongate, much compressed except along head, its depth about eight times in total length, tapering equally in front of, and behind, the midpoint of the body. Head very short, about 30 in total length, with the throat indented so that the head is clearly differentiated from the trunk; snout conical, about 3.0 in head, its dorsal profile slightly convex; nasal organ large, close in front of eye, with the nostrils not yet developed; eye small, 4.2 in head, round; cleft of mouth oblique, extending to below middle of pupil: teeth in both jaws acute but rather broad-based; an anterior grasping tooth in each jaw followed by a single series of teeth which gradually diminish in size posteriorly. Pectoral fin short, about 2.0 in postorbital, delicate, rounded; dorsal and anal fins with poorly developed rays, dorsal originating only a little in advance of 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 third to the last an oblique line of minute, compact, oval somatic chromatophores few in number anteriorly but increasing to about 16–20 in the middle of the body, decreasing in number along the caudal region; from the fifth segment to the origin of the dorsal fin a series of relatively large somatic chromatophores, 1–2 on each segment, along the dorsal midline; from the pectoral region to the posterior margin of the gall bladder on the body wall of the ventral midline, a regular series of small, compact chromatophores, 6–8 to each segment; posterior to this series, continuing to the vent, a paired, regular row of very small, dense, splanchnic chromatophores on the dorsal aspect of the intestine, about 12–14 for each segment; scattered small spots on the basal portions of many of the dorsal and anal fin-rays; a few spots over the base of the caudal fin; chorioid pigment present.
Remarks: The group of specimens described above agrees well with Strömman's 140mm specimen of L. scheelei from the Timor Sea, redescribed by Bertin (1936, pp. 3–5, fig. 4). This specimen has 114 myomeres of which 103 are preanal, the vent is almost subterminal, the eye is small and round, the nostrils are set closely together in front of the eye, the pectoral is small, pigment is distributed in an oblique line of minute, compact spots below the midlateral line on each myoseptum, in a series along the dorsal midline and on the dorsal, anal and caudal bases, all exactly as in present specimens of comparable length. Strömman (1896, p. 22) describes the ventral pigment as follows: "On the lower side for about the first fifth of the body's length there extends a row of pigmentary spots very close together especially at the hinder end. A little beyond where this row ceases, two other rows of spots begin, one on each side of the body; they run just above the alimentary canal and reach as far as the vent. These spots are so close together that to the naked eye they appear to form two continuous dark lines." This is exactly as found in the present specimens although the two posterior rows on the dorsal aspect of the intestine (actually following the kidney ducts) are so close together that they appear as one in some specimens.
Weber's specimen of L. indicus (1913, p. 74) from the Sulu Sea, 115.0mm total length, has pigment spots on each myoseptum (as in L. Ariosoma scheelei), spots on the bases of the dorsal, anal and caudal rays and 115 segments of which 73 are preanal. There are no larval teeth but a few definitive teeth are present. These characters suggest that the specimen is a metamorphosing specimen of L. Ariosoma scheelei. The present collection contains three specimens which are at metamorphosis, 119.2mm, 126.3mm and 131.0mm total lengths, all of which have about 80 preanal myomeres and are probably at a slightly earlier stage than Weber's specimen.
The same author describes as L. taenia Lesson, 34 specimens of L. Ariosoma scheelei from the Banda Sea and neighbouring areas. These larvae, 56mm–124mm in length, have about 115 segments, the vent is essentially subterminal and the pigmentation is similar to that found in Strömman's L. scheelei although Weber makes no mention of pigment on the dorsal midline. I am satisfied, nevertheless that these leptocephali are L. Ariosoma scheelei. On the other hand, a small specimen, 19.5mm total length, which Weber also refers to L. taenia lacks the characters which are possessed by L. Ariosoma scheelei of equal size. There are 106 myomeres, there is no pigment except in the chorioid but the vent is very close to the end of the body. Although in such a small specimen errors may be made in counting the posterior segments, specimens of L. Ariosoma scheelei page 7of comparable length in the present collection show large, conspicuous pigment spots along the dorsal and ventral margins, a feature which could not easily be overlooked.
Gopinath (1949, p. 93, text-fig. 1c, p1. 10) describes and figures 216 leptocephali from the Trivandrum coast of southern India, all as Congrellus anago. These specimens were 110mm–158mm total lengths with about 115 myomeres and they have pigment as in L. Ariosoma scheelei. So far as I can determine from his account all of them have about 78 myomeres before the vent, and this seems to have been the only reason for Gopinath regarding them as distinct from L. scheelei. However, they are all relatively large leptocephali and in this respect agree with Weber's specimen. They are probably undergoing metamorphosis. The single specimen, 90mm in length, described and figured by Deraniyagala (1934, pp. 91–92, fig. 1) as Larva I from the Pearl Banks in the Gulf of Mannar, Ceylon, has 114 myomeres of which 103 are preanal. Pigmentation in this specimen is not described but in view of the posterior vent and strong general similarity to L. Ariosoma scheelei I regard Deraniyagala's larva as belonging to this species.
Ancona (1928, pp. 17–27, p1. 2, figs. 1–4a) has described 27 leptocephali, 15.5mm–139mm total lengths as L. Ariosoma anago, from the Red Sea, which I regard as L. Ariosoma scheelei. Ancona's specimens have 112–117 myomeres (compared with the 149–159 of A. anago), the pigmentation is typical of L. Ariosoma scheelei in all stages of development and the vent is essentiallv subterminal.
Ancona examined a small (195mm) juvenile of "A. anago", but the radiograph showed only 119 vertebrae. Norman (1939, p. 39, fig. 12) describes and figures Ariosoma nigrimanus as so far the only known species of the genus from the Gulf of Aden. Norman does not give a vertebral count but in view of its area of capture A. nigrimanus is a possible adult of Ancona's leptocephali and juvenile.
Leptocephalus dentatus (Garman, 1899) with myomeres 121 and L. obtusus (Garman, 1899) with myomeres 119, from the Pacific coast of central America are possibly larvae of Ariosoma gilberti (Ogilby, 1898) as I have already suggested (Castle, 1963, p. 31). The only vertebral count available for the aduit is ca. 116 from the type of Thyreoconger hemiaspidus Wade, 1946, also from Pacific central America, which Rosenblatt (1958, pp. 52–54) has shown to be a synonym of A. gilberti. This gives a range of vertebrae for the latter as ca. 116–121, close to the range shown above for L. Ariosoma scheelei. Comparison of Norman's description and figure for A. nigrimanus and Wade's for Thyreoconger hemiaspidus (1946, pp. 189–191, p1. 25, figs. 1–3) shows a remarkable similarity between the two. If A. nigrimanus is the adult of Ancona's leptocephali and juvenile, the latter provide a vertebral count which would suggest that A. gilberti may be a synonym of A. scheelei.
Growth and Metamorphosis: The 67 specimens of L. Ariosoma scheelei range in length from 15.1mm to 154.8mm of which the majority are larvae at various stages of growth short of metamorphosis but three (96.7mm, 106.0mm and 119.4mm) are undergoing metamorphosis.
Number of Preanal Myomeres.—During active growth from 15mm to about 40mm the vent moves from about myomere 60 to myomere 105 in the total of about 115. The position of the vent then remains constant during further increase in total length. At 120mm to 130mm metamorphosis begins.
Number of Dorsal and Anal Fin-rays.—These can first be counted when the larva is only 40mm in length at which time they number about 50 in the anal and 60 in the dorsal. The origin of the dorsal fin is never appreciably in advance of the level of the vent in larvae prior to metamorphosis (even in individuals of 130mm), usually only about two myomeres in front of it, so that extremely rapid movement of the dorsal origin to its final position over the pectoral, must occur during metamorphosis.page 8
Teeth.—Although some specimens of L. Ariosoma scheelei (including the one described above) show little differentiation in size and grouping of teeth, most have teeth which are very similar to those of Gnathophis (see Castle, 1963, pp. 32–34). There is always an anterior grasping tooth in each jaw, which in the upper jaw is sometimes preceded by a small, needle-like tooth on the antero-dorsal surface of the snout; the grasping tooth is followed by a series of up to nine large teeth and then as many as 12 smaller teeth; there are always fewer posterior smaller teeth in the lower jaw. As in Gnathophis, as growth proceeds the bases of the larval teeth become overgrown by the fleshy snout and they appear to be relatively shorter in late leptocephali.
Pigmentation.—At 15mm the loptocephalus of Ariosoma scheelei has two minute, compact spots on each myoseptum below the midlateral line along the whole of the body except on the tip of the caudal region; dorsal pigment is restricted to about four large stellate spots along the dorsal midline; about four similar spots equally spaced along the midventral bodywall; a few compact spots on the dorsal aspect of the tip of the spinal cord. At about 30mm total length there are about 4–5 spots on. each myoseptum, about 18–20 dorsal spots, about 12 ventral spots and pigment on the tip of the caudal region. At the time when the posterior movement of the vent ceases (40mm) the dorsal spots become more compact, the caudal pigment is lost and the ventral stellate chromatophores are replaced by the small, somatic spots in a row on the ventral midline before the gall bladder and the two rows of minute, compact spots on the dorsal aspect of the intestine. Spots on the bases of the dorsal and anal rays begin to form at about 50mm total length.
Geographical Range and Location of Spawning Areas (Text-fig. 2, A)
Except for the two metamorphosing specimens of L. Ariosoma scheelei beachcast at Sydney and a single, nearly full-grown larva collected off Rottnest Island, Western Australia, all of the present material, that is, 64 specimens, came from the area included by the Solomons, New Hebrides and New Caledonia. The leptocephali are rare and the adult, if present, may be very rare in the Australian region. Small specimens of from 15mm to 35mm were collected in the area immediately surrounding New Caledonia and New Hebrides in 20–120 metres. Larger specimens are more widely distributed. It is therefore probable that spawning of Ariosoma scheelei in the southwest Pacific occurs in the waters around New Caledonia. In consideration of the size of specimens previously recorded from the Banda and Sulu Seas and neighbouring areas by previous authors it is likely that larvae move from the New Caledonia region westwards through the Malayan Archipelago as well as occasionally to Western and Eastern Australia. Ancona's studies of this species shows that it must also spawn in the Red Sea since his smallest specimen was 15.5mm total length; Gopinath's 216 larvae from southern India are all very large and it is unlikely that the species spawns in this area; these larvae are probably derived from the Red Sea.
Should A. gilberti from the Pacific central America finally prove to be a synonym of A. scheelei, the geographical range of the latter will extend across the whole of the Indo-Pacific. Briggs (1961, p. 552) lists seven species of shallow-water tropical eels which have a similar distribution, a relatively high number of trans-Pacific species for any one group of shore fishes. Generally the trans-Pacific species which Briggs lists are active pelagic fishes in which such a distribution can be explained in part by their ability to move about for some distances independent of the bottom. Others, like the eels and including Albula vulpes and Chanos chanos, have an extended pelagic larval life.