Conger melanopterus, Kodeeswaran & Smith & Dhas & Ajith Kumar & Lal, 2023

Kodeeswaran, Paramasivam, Smith, Id. G., Dhas, Deepa, Ajith Kumar, T. T. & Lal, Kuldeep Kumar, 2023, A new species of the congrid eel genus Conger (Anguilliformes: Congridae) from the southwest coast of India, Zootaxa 5244 (5), pp. 474-484 : 475-483

publication ID	https://doi.org/ 10.11646/zootaxa.5244.5.4
publication LSID	lsid:zoobank.org:pub:B9DA5563-B5EE-44C8-A96E-E9B6BF8377DD
DOI	https://doi.org/10.5281/zenodo.7667624
persistent identifier	https://treatment.plazi.org/id/6B6887C2-FFB9-A415-5DB3-FACDFEF3FCD9
treatment provided by	Plazi
scientific name	Conger melanopterus
status	sp. nov.

Treatment

Conger melanopterus , new species

New English Name: Indian Black-fin Conger

( Figures 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ; Tables 1–3 View TABLE 1 View TABLE 2 View TABLE 3 )

Holotype: NBFGR /CONCMEL, (569 mm TL, spent female) collected from deep-sea trawl, Colachel fishing harbour (8°10′21.92″N, 77°15′2.98″E), Southwest coast of India, Indian Ocean, Deepa Dhas, D. S., 08 July 2021. GoogleMaps

Diagnosis. A moderate sized dark-coloured eel of the genus Conger , distinguished from its congeners by having the following combination of characters: dorsal-fin origin behind the pectoral-fin tip; larger head, 18.5% TL; longer predorsal length 24.0% TL; relatively shorter trunk, 52.4% PAL; smaller eye, 12.9% HL; trunk length is 1.1 times in head length; vomer with seven uniserial teeth at posterior end; body fully blackish to dark brown; pectoral fin much darker than body; cephalic pores with whitish rims; SO pores 3; first two pores located at snout tip; small adnasal pore, which is positioned adjacent to third SO pore; IO pores 6, 5 before rictus and 1 behind rictus; pectoral rays 19; total vertebrae 141+.

Description. Morphometric measurements in proportion of total length: head length 5.4 in TL; preanal length 2.5; predorsal length 4.2; trunk length 4.7; tail length 1.7; depth at gill opening 15.6. Measurements in proportion of head length: snout length 4.0 in HL; eye diameter 7.7; interorbital width 6.1; upper jaw 2.8; gill opening width 6.8; interbranchial width 3.7; pectoral fin 3.3. Meristic data and morphometric proportion of % TL, PAL and HL are provided in Table 1 View TABLE 1 .

Moderately elongate eel with anus positioned before mid-length, preanal length 40.6% TL. Relatively slender tail with flexible caudal fin. DFO behind pectoral-fin tip, predorsal length 24.0% of TL and continuous with caudal and anal fins. Snout moderate, fleshy part projecting slightly beyond intermaxillary tooth patch. Head relatively large, 18.5% TL. Anterior nostril rather large; posterior nostril moderate pore in front of eye. Both jaws almost equal in length with well-developed flanges. Tongue large and broad, anterior half free from mouth floor, with pointed tip.

Head pores small, positioned on head instead of flanges. SO pores 3; first two pores located at snout tip; small adnasal pore, which is positioned adjacent to third SO pore. IO pores 6; 5 before rictus and 1 behind rictus. ST canal with 1 pore; preoperculo-mandibular pores 9, 6 before rictus and 3 behind rictus ( Fig. 3 View FIGURE 3 ). Lateral line almost complete, pores inconspicuous; 5 prepectoral pores, 13 predorsal pores, 34 preanal pores and 138 total pores.

14 predorsal vertebrae; 36 preanal vertebrae; 141+ total vertebrae; 19 pectoral rays.

Teeth small, pointed or blunt and acute. Rounded intermaxillary tooth patch with 4 transverse rows, not well separated from maxillary and vomerine teeth. Maxillary and dentary teeth in two rows, those of outer row pointed, those of inner row blunt and reaching more than half length of outer maxillary rows. Vomerine teeth pointed or blunt, forming a long patch, 3 or 4 transverse rows in the anterior portion, followed by seven uniserial teeth posteriorly ( Fig. 4 View FIGURE 4 ).

Morphometric data of holotype (in mm): TL 569, HL 105.4, depth at gill opening 36.4, depth at anus 35.7, predorsal length 136.7, preanal length 231.2, trunk length 121.0, tail length 333.5, snout length 26.4, eye diameter 13.6, interorbital width 17.2, upper jaw length 37.2, gill opening width 15.5, interbranchial width 28.3, pectoral fin length 32.4.

Colouration. For general appearance see Figs. 1 View FIGURE 1 & 2 View FIGURE 2 . Body uniformly blackish to dark brown (not much brown), median fin bases and distal margins also black ( Figs. 1 View FIGURE 1 & 2A View FIGURE 2 ). Ventral surface of head blackish; anterior nostril pale pinkish to brown; rims of cephalic pores milky white ( Figs. 2B, 2C View FIGURE 2 ). Inner surface of flanges whitish; tongue white to pale brown with numerous melanophores on side margins and lower surface, but not at the tip. Pectoral fin completely black, much darker than body. In preservative: body remains the same, but darker than when fresh.

Etymology. The species name “ melanopterus ” derived from two Greek words melano (μελανός) = black and pterus (πτερόν) = winged, denotes black pectoral fin.

Distribution. Southwest coast of India, Arabian Sea, Indian Ocean. The species was collected at a depth of 300 m along the EEZ of Indian Waters in the Western Indian Ocean.

Molecular analysis. The K2P genetic analysis reveals that new the species is closely related to C. verreauxi from Australian waters with a divergence of 5.7%. Further, the genetic divergence between the new species and C. macrocephalus from Indonesian and Taiwan waters was 5.9%. The new species differs from the species commonly treated as Conger wilsoni ( Bloch & Schneider, 1801) in Australian waters and Conger myriaster ( Brevoort, 1856) from Taiwan waters with 6.4% and 6.8% divergence respectively. The new species shows a maximum genetic divergence between Conger triporiceps Kanazawa, 1958 with 22.7%, followed C. cinereus with 22.0%, Conger oceanicus ( Mitchill, 1818) with 15.2%, and Conger orbignianus Valenciennes 1837 with 15.1% and Conger conger ( Linnaeus, 1758) with 10.9% ( Table 2 View TABLE 2 ). In the maximum likelihood tree (Fig. 6), C. melanopterus forms a distinct lineage sister to known congeners with high bootstrap values supporting the status as a new species.

Comparison. Conger melanopterus differs from all other congeners but shares few characters with C. macrocephalus such as larger head 18.5% (vs. 15.4–21.0% in C. macrocephalus ) and maxillary teeth with 2 rows. It differs from C. macrocephalus in having more total vertebrae (141+ vs. 132–139), a larger gill opening length (14.7% HL vs. 10.7–13.1% HL), trunk length 1.1 times in head length (vs. 1.2–1.6), smaller eye (12.9% HL vs. 13.7–18.7%), shorter tail (58.6% TL vs. 59.3–62.2% TL), more pectoral rays (19 vs. 17), pectoral fin completely dark (vs. pale or with large black patch), body completely dark including median fins and margin (vs. pale greyish to brown, median fins whitish with black margin) and vomerine teeth forming seven uniserial teeth in posterior end (vs. vomerine forming short patch, see Fig. 3C View FIGURE 3 in Smith & Ho 2018) ( Smith et al. 2017; Smith & Ho 2018).

Conger melanopterus differs from the Indian congener, C. cinereus , in having more predorsal vertebrae (14 vs. 9–11), longer predorsal length (24.0% vs. 12.8–14.1% TL), DFO behind the pectoral-fin tip (vs. DFO at middle of the pectoral fin), pectoral fin completely dark (vs. dark spot on pectoral fin), maxillary teeth in 2 rows (vs. 1), and larger head (18.5% vs. 11.5–12.7% TL) ( Smith & Ho 2018). The new species further differs from C. conger , Conger marginatus Valenciennes, 1850 , C. orbignianus , C. triporiceps , C. verreauxi , and C. wilsoni in having fewer vertebrae (141+ vs. 148–161 in C. conger ; 148–153 in C. marginatus ; 160–161 in C. orbignianus ; 156–160 in C. triporiceps ; 152–157 in C. verreauxi ; 146–147 in C. wilsoni ) ( Kanazawa 1958). Further, C. melanopterus differs from Conger esculentus Poey, 1861 , Conger oligoporus Kanazawa, 1958 and Conger philippinus Kanazawa, 1958 in having more total vertebrae (141+ vs. 132–133 in C. esculentus ; 136–139 in C. oligoporus ; 127–135 C. philippinus ) ( Kanazawa 1958; Smith & Ho 2018).

The new species shares total vertebrae and body colouration with Conger jordani Kanazawa, 1958 , but is readily distinguishable from the latter in having 3 SO pores (vs. 4), trunk length 1.1 in times the head length (1.4–1.9), vertical fins bases black (vs. white), larger head (18.5% TL vs. 13.3–14.3%), smaller eye (12.9% HL vs. 15.5–17.1% HL), trunk length 52.4% PAL (vs. 59.6–64.5% PAL), longer predorsal length (24% TL vs. 18.8–20.6% TL), and shorter tail (58.6% TL vs. 61.7–64.7% TL) ( Kanazawa 1958; Smith & Ho 2018).

The new species shares similar total vertebrae, pectoral rays, and colouration with Conger erebennus ( Jordan & Snyder, 1901) from the Western North Pacific. But it readily differs from the latter in having fewer preanal vertebrae (36 vs. 40–42), preanal pores (34 vs. 37–40), head larger (18.5% HL vs. 16.3–17.3% HL), and pectoral fin 3.3 in HL (vs. 3 in HL) ( Jordan & Snyder 1901; Kanazawa 1958; Smith et al. 2016).

Conger myriaster from the waters off Japan, Taiwan and China has a close total vertebrae count to C. melanopterus , and one specimen from Taiwan shares similar body colouration (See Fig. 6C in Smith & Ho 2018). But C. melanopterus readily differs from C. myriaster in having a larger head (18.5% TL vs. 12.3–14.9% TL), longer predorsal length (24.0% TL vs. 17.7–18.9% TL), trunk length 52.4% PAL (vs. 61.8–67.9% PAL), relatively smaller pectoral fin (30.7% HL vs. 35.9–43.1% HL), trunk length 1.1 times in head length (vs. 1.6–2.1), and maxillary teeth inner row ½ of outer row (vs. short) ( Smith & Ho 2018).

Remarks. Although several species of the genus Conger undergo changes in body colour, variation in pectoral fin shape, eyes shape, tooth loss and vertebral decalcification during maturity (see Smith & Ho 2018; Battaglia et al. 2020), the new species is significantly different in that teeth are retained and vertebral decalcification is not as intense and in possessing a larger head than all other species except C. macrocephalus , but differs from this species in other characters and genetically. We described the first new species of the genus Conger in 65 years. This joins C. cinereus and C. wilsoni as the third species of Conger known from the Western Indian Ocean. Further attempts to collect additional specimens were unsuccessful due to the difficulty of deep-sea collection and rarity. Though the species of the genus Conger are well-known for their large size and commercial value, knowledge of the taxonomic status and diversity of the species is limited ( Smith & Ho 2018). After Kanazawa (1958), no new species have been described from this genus until now, and only a very few authors such as Asano (1962), Castle (1964, 1968), Smith (1989) and Smith & Ho (2018) had worked on the systematics of the genus Conger . Hence, the revision of this genus along with both morphological and phylogenetic analysis is needed to resolve the taxonomic and diversity ambiguity.