L. Gnathophis incognitus

Material Examined. C.S.I.R.O. Division of Fisheries and Oceanography (Cronulla) Collection (45 specimens,: 5.3mm total length, Warreen Station 44/39, 34° 02′ S., 151° 15.5′ E, 26/1/39, N100 (100cm net), H (horizontal tow), surface, 30mins; 5.5, 7.8, St 32/40, 34° 04′ S., 151° 14.5′ E., 25/4/40, N70, H, surface; 5.7, St 3/40, 32° 47′ S, 152° 40′ E, 11/1/40, N100, O, 0-200m; 5.9, St 32/40, 34° 04′ S., 151° 14.5′ E., 25/4/40, N70, O, 50m; 6.2, St 7/40, 30° 13′ S., 153° 33′ E., 14/1/40, N70, O, 200m; 6.6, St 32/40, 34° 04′ S., 151° 14.5′ E, 25/4/40, N70, H, surface; 7.2, 8.9, 8.9, off Eden, Victoria, 1/4/48; 8.2, ca. 9.6, Discovery St 2723, 34° 08′ S., 151° 33′ E., 9/10/50, N100B, 93-0m; 8.6, Warreen St 139/39, 31° 51.5′ S., 152° 50′ E, 17/5/39, N100, H, 25m, 60mins; 9.0, Kywong, 18° 46′ S., 147° 15′ E, Keeper Reef, Great Barrier Reef, 24/11/51. 50cm/40mesh net, surface, 15mins; 10.9, 12.8, Discovery St. 2722, 34° 04′ S., 151° 50′ E., 9/10/50, N100B, 114-0m; 12.0, 14.9, Warreen St 127/39, 33° 18′ S. 152° 13′ E., 3/5/39, N100, H, 100m, 30mins; 12.1, 14.0, St 105/39, 41° 17′ S. 148° 26′ E., 10/4/39, N200, H, 25m, 30mins; 12.1, St 132/39, 30° 15′ S., 153° 33′ E., 5/5/39, N100, H, 100m, 60mins; 12.4, St 24/40, 34° 08.5′ S., 151° 36.5′ E., 27/2/40, N70, O, 200m; 12.8, St 30/40, 30° 18′ S., 153° 32′ E., 22/4/40, N100, O, 200m; 19.8, St 22/42, 39° 46′ S., 148° 36′ E., 18/4/42, N70, H, 50-0m; 22.0, St 48/39, 35° 07′ S., 150° 50′ E, 7/2/39, N200, H, 25m, 30mins; 23.9, 24.3, 133.9, 138.8, St unknown, ca. 34° 04′ S., 151° 15′ E., ?/39, no other data; 25.0, 26.0, St 141/39, 34° 04′ S., 151° 15′ E, 30/5/39, N100, H, surface, 30mins; 25.7, St 144/39, 36° 15′ S., 150° 25′ E, 31/5/39, N200, H, 100m, 30mins; 26.0, St 142/39, 35° 03′ S., 151° 08′ E., 30/5/39, N70, V, 50-0m; 26.9, 30.1, St 183/39, 43° 13′ S., 148° 19′ E, 11/6/39, N200, H, 100m, 30mins; 28.2, St 140/39, 34° 09′ S, 151° 35′ E., 29/5/39, N100, H, 100m, 30mins; 78.5, Derwent Hunter St DH 94/55, 42° 50′ S., 150° 50′ E., 27/8/55, Hardy recorder, surface; 85.9, Warreen St 21.4/39, 36° 14′ S., 150° 25′ E., 3/9/39, N70, O, 200m; 95.9, 97.2, St 224/39, 35° 03′ S., 151° 09′ E., 4/10/39, N200, H, surface; 102.6, St 5/39, 35° 09′ S., 151° 06.5′ E, 6/1/39, N200, H, 100m, 30mins; 121.1, 138.8, St 185/39, 42° 37′ S., 148° 32′ E., 11/6/39, N200, H, 100m, 30mins; 133.3, Discovery St 2709, 37° 06′ S, 150° 35′ E, 5/10/50, N100B, 110-0m; 138.7, Derwent Hunter St DH 80/53, Maria Island wide, 2/10/53, N70, H surface; 141.0, Discovery St 2710, 37° 06′ S., 150° 48′ E., 6/10/50, N100B, 84-0m.

Australian Museum Collection (1 specimen): 135.1, Aust. Mus. regd. no. IA.2058, no other data.

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Western Australian Museum Collection (3 specimens,: 44.2, Accession No. P5234, Lancelin, 46 miles west of West End, Rottnest Island, Western Australia, 11/4/62 (0200hrs), larval net in 37 metres; 86.2, P5279, 39mls, 7/6/62 (0500–0530), In, 37m; 120.0, P5233, 49mls, 9/5/62 (0100–0130), In, 37m.

Centre d'Océanographie de l'Institut Français d'Océanie Collection (15 specimens,: 22.7, IFO Station MWT 2, 10 miles west of the Bulari pass, off Nouméa, 30/11/61, 3ft midwater trawl (Isaacs-Kidd), H, 68m; 24.3, 26.6, 27.5, 28.2, St S 1m 6, 10mls west of Bulari pass, 30/11/61, 1.0m net, 117m; 24.9 St 7-2, 22° 35′ S., 166° 16′ E., 17/7/62, 5ft midwater trawl (Isaacs-Kidd), H, ca. 70m; 25.0, St S 6, 11° 51′ S., 159° 13′ E., 11/6/62, 5ft midwater trawl (Isaacs-Kidd), H, ca. 95m; 25.0, St S 1m B, 10mls west of Bulari pass, 28/11/61, 1.0m net, H, 90m; 25.2, St S 1m 1, 10mls west of Bulari pass, 30/11/61, 1.0m net, H, 68m; 28.3, St 7-8, 22° 35′ S., 166° 16′ E, 26/7/62, 5ft midwater trawl (Isaacs-Kidd), H, ca. 20m; 39.8, St MWT 3 I, 10mls west of Bulari pass, 1/8/61, 3ft midwater trawl (Isaacs-Kidd), H, 23m; 65.2, St D 6b, 18° 22′ S., 158° 15′ E., 15/5/60 (0211), 0.5m net, no. 2 mesh, 2 oblique tows in 0–300m; 67.0, St S 10, 17° 40′ S., 162° 25′ E, 22/6/62, 5ft midwater trawl (Isaacs-Kidd), H, ca. 95m: 82.7, St 57-5-4, stomach of yellow fin tuna (Neothunnus macropterus, longlined at 21° 33′ S., 166° 32′ E., 11/9/57; 94.1, St MWT 3 I, 10mls west of Bulari pass, 1/8/61, 3ft midwater trawl (Isaacs-Kidd), H, 40m.

New Zealand Collections (3 specimens,: 126.0, Dom. Mus. No. 2131, Dom. Mus. St. 210, net 4, Bay of Plenty, Feb/57, cone-net, 400m; 132.0, Dom. Mus. No. 1771, beachcast at Lake Ferry outlet, Palliser Bay, 17/9/55; 143.2, Dom. Mus. No. 1601, outlet at Lake Ferry, Palliser Bay, 13/10/54, whitebait net.

Description. 68 specimens: total lengths 5.3mm-143.2mm, myomeres 134–150, dorsal fin-rays 175–269, anal fin-rays 130–184. Vertical blood-vessels at 11, 37, 46. Anterior margin of gall-bladder at about myomere 37. a–d = ca. 33.

Remarks. Larvae of Gnathophis incognitus are very closely similar to those of G. habenatus but may be distinguished from the latter mainly in having a greater number of myomeres. Text-fig. 8 shows the number of myomeres in larvae of the two species. The greatest proportion of specimens of G. incognitus have 143 myomeres while G. habenatus has 123 and the ranges of the two species do not overlap. The two species are therefore easily distinguished on this character alone, but there are other features which separate the two.

G. incognitus has the last vertical blood-vessel at myomere 46 and preanal myomeres numbering about 112 during the major part of the growth period of the larva. This may be compared with G. habenatus, which has the last vessel at myomere 41 and the preanal myomeres numbering about 100. There are slightly more numerous dorsal and anal fin-rays in G. incognitus.

Some of the small larvae identified as G. incognitus may possibly be referable to species of Conger since at the time of writing there are no known characters which could be used to separate very young larvae of the two genera, Conger and Gnathophis. At this early stage the differences in pigmentation which are the major characters by which older larvae of the two genera are separated are insufficiently developed to be useful. Conger wilsoni (Bloch & Schneider, 1801) with 146–147 vertebrae (Kanazawa, 1958, p. 257) and C. cinereus cinereus Rüppell, 1828, which has 139–147 vertebrae (Kanazawa, 1958, p. 235) may be the two species confused in these identifications. The former is a common species in eastern Australia and northern New Zealand, and the latter has been recorded from North Queensland (Whitley, 1935, p. 219).

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Growth and Metamorphosis. Similar changes in shape of myomeres, number of preanal myomeres, number and distribution of teeth, etc., and distribution of pigment take place in the growth of leptocephali of G. incognitus as already described for G. habenatus. The 68 specimens range in total lengths from 5.3mm to 143.2mm. Text-fig. 9 shows that during the earlier stages of growth from loss of the yolk-sac at about 5mm to a length of 30mm there is a rapid increase in the number of preanal myomeres from 35% to 80% of the total. There are insufficient larvae in stages of metamorphosis to state when this normally takes place in G. incognitus although one specimen from New Caledonia at 82.7mm total length has preanal myomeres about 55% of the total, indicating that metamorphosis is well under way. On the other hand, many of the other late larvae are at the same stage of metamorphosis at a total length of about 120mm-130mm. The larvae of this species appear to reach a greater maximum size than do those of G. habenatus, there being 12 specimens over page 45 120mm total length in the collection of 68 specimens compared with only 2 specimens in the 154 of G. habenatus. Three early elvers of G. incognitus, total lengths 70.0mm, 80.1mm and 84.3mm from the Kermadec Islands by their colouration have evidently just undergone metamorphosis. The late glass-eel of G. habenatus from Western Australia already described is 61.2mm total length so it is possible that G. incognitus indeed has larger leptocephali and elvers.

Geographical Range and Location of the Spawning Areas. The 68 larvae of G. incognitus were collected from about the same area as were those of G. habenatus. A total of 46 of these larvae were collected on the east Australian coast mainly between 20° S. and 40° S. along the New South Wales coast and off Tasmania with a single specimen from the Great Barrier Reef, North Queensland. Fifteen larvae were taken off New Caledonia; three larvae were collected in the New Zealand region; but only three specimens were collected off the west Australian coast. The smallest leptocephali were taken from the same general locality off the New South Wales coast as were the smallest larvae of G. habenatus, while the largest were taken again on the periphery of the area of distribution—that is, from Tasmania to New Zealand. However, like G. habenatus, a number of the larger leptocephali were collected with the smaller larvae off New South Wales. Spawning of this species would therefore appear to take place in about the same area off eastern Australia as does G. habenatus. However, compared with the latter species there would seem to be two differences in distribution of G. incognitus (a) larvae are more abundant in the New Caledonia region, (b) larvae are much less abundant, even rare, off Western Australia, although a limited spawning probably takes place here also.

Bathymetric Distribution. No precise figures are available for the depths at which the leptocephali of G. incognitus are more abundant, but the range of depths of the tows in which this species were collected is 0m-400m with the larvae more frequent in 50m-100m.