Conger myriaster ( Brevoort, 1856 )

Smith, David G. & Ho, Hsuan-Ching, 2018, Review of the congrid eel genus Conger (Anguilliformes: Congridae) in Taiwan, Zootaxa 4454 (1), pp. 168-185 : 178-180

Conger myriaster ( Brevoort, 1856)

Figs. 2B , 3D , 6 ; Table 2

Anguilla myriaster Brevoort, 1856:282 , pl. 11, fig. 2 (Type locality: Hakodate, Hokkaido, Japan. No types known).

Conger myriaster: Lee & Yang, 1966:56 , fig. 4; Chen & Weng, 1967:48; Chen, 1969: 132; Shen, 1984:112; Chen & Yu, 1986:252; Shen et al., 1993:116; Shao et al., 2008:239; Ho et al., 2010:table 1.

Conger japonicus Bleeker, 1879:32 , Pl. 2, fig. 2 (Type locality: Japan. Holotype: ZMH 3748).

Specimens examined. 21 specimens, 154‒840 mm TL. Taiwan: * NMMB-P4983 (1, 545), Penghu , Taiwan Strait, 1 Aug. 1957. * NMMB-P6392 (1, 423), Daxi, Yilan , 23 Jan. 1994. * NMMB-P11172 (1, 473), Dong-gang , 15 Dec. 2009 . * NMMB-P12216 (1, 554+), Daxi , Yilan, 22 Jan. 2010 . NMMB-P27758 (1, 840), Daxi , Yilan, 1 Jul. 2017 . USNM 439338 (1, 515+), mature male, Daxi , Yilan, 29 Jun. 2007 . Other localities: Japan: * USNM 49977 (6, 154‒440), Tokyo Prefecture , Honshu Island. * USNM 75981 (1, 509), off Honshu Island , 379‒457 m, 12 May 1900 . * USNM 151740 (1, 563), Fukui , Japan, Oct.-Nov. 1922. * USNM 151793 (1, 227), Honshu , Japan , Oct.-Nov. 1922 . ZMH 3748 (1, 329, holotype). China: * USNM 130468 (3, 315‒367), Tsingtao , Shandong , Aug. 1926. * USNM 328953 (1, 304) and * USNM 329102 (1, 301), Shandong , 26 Jul. 1993.

Diagnosis. DFO over posterior half of pectoral fin. Inner row of teeth in lower jaw more than half the length of outer row ( Fig. 3D ). Vertebrae 142‒148. A row of white spots on body above lateral line, lateral-line pores and sensory papillae on head white.

Description. See Table 1 for morphometric data. Lateral-line pores: prepectoral 5‒6; predorsal 12‒13; preanal 38‒42; total 134‒141. Head pores ( Fig. 2B ): SO 4, IO 6 (5 on upper jaw + 1 behind rictus), POM 9 or 10 (6 or 7 on lower jaw, 3 behind rictus), ST 1. Vertebrae: predorsal 13‒16; preanal 39‒44; total 142‒148; MVF 14-42-145.

DFO over posterior part of pectoral fin. Angle of jaw before posterior margin of eye, 6th IO pore at level of and more than one pore diameter behind rictus ( Fig. 2B ). Two rows of teeth on each jaw; inner row of maxillary teeth short, inner row of dentary teeth about 1/2 to subequal of length of outer row ( Fig. 3D ). When preserved, dorsal surface light grayish, ventral surface paler; a row of white spots on side of body above lateral line, lateralline pores and sensory papillae on head white.

Maximum size 1000 mm TL ( Masuda et al., 1984).

Distribution. Known from Japan, Taiwan and China.

Remarks. NMMB-P12216 has only a few teeth on the inner row of the upper jaw and a somewhat shorter inner row, about 1/2 the length of the outer row on the lower jaw. Kanazawa (1958) also mentioned some of his specimens have only a few teeth in the inner row, thus it is treated as individual variation.

NMMB-P4983 has a few teeth on the inner row of the upper jaw and a shoewhat shorter inner row (about 1/2 of outer row) of teeth on the lower jaw. The DFO is well behind the pectoral fin. The head pores are similar to the others. The tooth pattern is identical to NMMB-P12216. However, the color of NMMB-P4983 is somewhat faded, so it might be a C. myriaster with a posterior DFO.

Life history and reproduction. Conger myriaster is the most common species of Conger in Japan and is an important commercial species. At least some species of Conger , like those of Anguilla, undertake long spawning migrations to areas of deep water far from shore. Also, like Anguilla, species that live in temperate waters appear to travel greater distances than those of the tropics. Very young larvae of ca. 5‒6 mm in length have recently been collected in the western North Pacific along the Kyushu-Palau Ridge ( Miller et al., 2011; Kurogi et al., 2012), slightly to the north and west of the spawning ground of Anguilla japonica. From there, the larvae are carried back to the coast by the prevailing currents. The larvae were identified genetically by matching the sequences of the mitochondrial 16s rRNA and cytochrome oxidase I with the comparable genes in adult Conger myriaster .

Although spawning areas have been located by finding the newly hatched larvae, adults have still not been collected in the open ocean. The adults leave the coast before becoming fully mature and apparently never return. They mature, spawn, and die in the open ocean. Cunningham (1891‒92) described his observations on maturing Conger conger in an aquarium in Plymouth, England. He reported finding a “perfectly ripe male” and described its appearance:

“ It was quite a small specimen and somewhat thin; the peculiarities about it were its large prominent eyes and short broad snout. The eyes were so large in proportion to the head that their upper edges project[ed] slightly above the dorsal surface of the skull, and that surface between the eyes was quite depressed and hollow. ”

He later reported that both ripe males and females had lost most of their teeth and the bones of the head had become soft and flexible. He also noted that they stopped feeding. Unfortunately, he did not illustrate either the males or the females. As such specimens are not found naturally in coastal waters, it seems likely that they mature only after they have reached the spawning area.

We report here the collection of a specimen (USNM 439338, 515+ mm TL), from a market in northeastern Taiwan that appears to be a mature male ( Fig. 6C ). It is very different in appearance from all the other specimens: uniformly black with a relatively large head and narrow body, a long pectoral fin, and a large eye. The gut is empty, and well-developed testes are present. The snout has a rather deep, squared-off appearance, and the flange on the upper lip is greatly reduced. Indeed, it would have been difficult to recognize as a Conger had its identity not been confirmed through DNA analysis. The CO1 sequence (Genbank accession MF172257 ) was blasted against the BOLD database to find the closest match. The result, based on 19 specimens, was a 99.84‒100 percent match with Conger myriaster .

Morphological characters confirm the identification. The dentition is typical of Conger , as is the number and arrangement of pores and the position of the dorsal-fin origin over the end of the pectoral fin. Most notable is the presence of an adnasal pore in close proximity to the third SO pore, giving the appearance of a double pore, a diagnostic feature in Conger . There are no morphological characters that would falsify this identification. The specimen is missing part of the tail, and the body is badly abraded. The bones are soft and pliable, and the teeth are small and weak. The tip of the tail is missing, and 138 vertebrae are present. The specimen is 515 mm in length. The proportions are nearly normal, however, and the number of vertebrae is only slightly lower than normal, indicating that only a small portion of the tail has been lost. The specimen was collected from a market in northeastern Taiwan, but the exact location of capture is not known.

Figures

FIGURE 2. Line drawings demonstrating the arrangement of head pores of two species. A. C. cinereus. B. C. myriaster. Bar indicates the ST pore.

FIGURE 3. Demonstration of jaw tooth pattern of five Conger species in Taiwan. A. C. cinereus, from NMMB-P24265. B. C. jordani, from NMMB-P24766. C. C. macrocephalus, NMMB-P15401. D. C. myriaster, NMMB-P6392. E. C. philippinus, NMMB-P22425. Note that the numbers of principal teeth are not counted from the specimens.

FIGURE 6. Conger myriaster (Brevoort, 1856). A. NMMB-P27758, 840 mm TL. B. NMMB-P11172, 473 mm TL. C. USNM 439338, mature male, 515+ mm TL.