Research Article |
Corresponding author: Thipramalai Thangappan Ajith Kumar ( tt.ajith@icar.gov.in ) Academic editor: Nalani Schnell
© 2024 Paramasivam Kodeeswaran, Ayyathurai Kathirvelpandian, Dipanjan Ray, Anil Mohapatra, Thipramalai Thangappan Ajith Kumar, Chelladurai Raghunathan, Uttam Kumar Sarkar.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kodeeswaran P, Kathirvelpandian A, Ray D, Mohapatra A, Kumar TTA, Raghunathan C, Kumar Sarkar U (2024) Two new species of the congrid eel genus Ariosoma (Anguilliformes, Congridae, Bathymyrinae) from Indian waters. Zoosystematics and Evolution 100(1): 119-128. https://doi.org/10.3897/zse.100.116611
|
Two new species have been described from Indian waters, based on the materials collected from Kochi coast, Arabian Sea, Gulf of Mannar and West Bengal coast along the Bay of Bengal. Ariosoma gracile sp. nov. is described, based on five specimens collected from the landings at Kalamukku Fishing Harbour, Arabian Sea. The new species is characterised by longer tail, 55.3–58.7% TL; dorsal-fin origin above pectoral-fin base; no dark or whitish bands on dorsal surface of head, ventral extremities of lower jaw and mid-portion with minute dark pigmentation patch; anus positioned well before the middle of total length; SO canal with 4 pores; 0 or 3 pores on ST canal; pre-dorsal vertebrae 9; pre-anal vertebrae 49–54; total vertebrae 140–142. Ariosoma gracile sp. nov. is closely related to Ariosoma dolichopterum and Ariosoma emmae by sharing similar morphometrics and pre-anal vertebral counts. However, it differs by having more total pores (132–135 vs. 121–129 in A. dolichopterum, 123–126 in A. emmae); fewer pre-anal pores (43–46 vs. 47–51 in A. dolichopterum, 50–53 in A. emmae); more pre-dorsal pores (9 vs. 5–9 in A. dolichopterum, 4–6 in A. emmae). Another new species, Ariosoma kannani sp. nov. is described on the basis of two specimens (157–171 mm TL) from Gulf of Mannar and one specimen (201 mm TL) collected from Shankarpur Fish Landing Centre, West Bengal. This species is similar to Ariosoma megalops, but readily differs by having smaller eyes, smaller interorbital distance and exhibits 10.8% genetic divergence from A. megalops from the Taiwan waters.
Arabian Sea, Bathymyrinae, Bay of Bengal, new eel, systematics
The congrid eel genus, Ariosoma Swainson, 1838, includes 38 valid species (
Eel samples were collected from different landing centres along the India coast viz. Kalamukku Fishing Harbour (9°59'N, 76°14'E), off Kerala coast, west coast of India, Arabian Sea and Rameshwaram Fish Landing Centre (9°16'N, 79°18'E), Tamil Nadu, Gulf of Mannar, east coast of India, Bay of Bengal and Shankarpur Fish Landing Centre, West Bengal, Bay of Bengal, India. Fresh photographs were taken with a Canon 80D Digital Single-Lens Reflex camera (EF-S 18–135mm f/3.5-f/5.6 IS USM Kit Lens) and a small portion of muscle and pectoral fin-clips were incised and preserved in 99.9% ethanol for phylogenetic analyses. Collected specimens were preserved in 10% formaldehyde for taxonomical studies and deposited in the
National Fish Museum and Repository of the ICAR–National Bureau of Fish Genetic Resources (
Morphometric measuring and meristic counting follow
The DNA isolation, PCR cycle conditions and mtDNA gene amplifications were done, based on the methods followed in
Ariosoma albimaculatum.
Ariosoma bengalense. F12898, holotype (304 mm TL), collected from Petua Ghat, West Bengal, India from the depth of 168 m; EBRC/ZSI/F12899, paratype (216 mm TL), data same as holotype.
Ariosoma gnanadossi. ZSI F7146/2, holotype (283 mm TL), collected from the depth of 250 m, off Madras, east coast of India, Bay of Bengal.
Ariosoma indicum.
Ariosoma majus. EBRC/ZSI/F 11528 (2 specimens: 246–290 mm TL) collected from Deshpran Fishing Harbour, West Bengal, east coast of India, Bay of Bengal.
Ariosoma maurostigma.
Ariosoma melanospilos.
Ariosoma sp.
Holotype.
Paratypes.
A medium-sized slender eel species of Ariosoma distinguished from all other species by the following combination of characters: position of anus well-before middle of total length, pre-anal length 43.7% (41.3–44.7%) of TL; tail longer, 55.3–58.7% TL; dorsal-fin above pectoral-fin base; no dark or whitish bands on dorsal surface of head, ventral extremities and mid-portion of lower jaw with minute dark pigmentation patch; short vomerine teeth patch with three or four rows of pointed teeth in anterior portion, intermaxillary teeth patch curved, slightly upturned at anterior end, clearly visible when mouth closed, separated from vomerine and maxillary teeth by a definite gap; SO canal with 4 pores; 0 or 3 pores on ST canal; pre-dorsal vertebrae 9 (9); pre-anal vertebrae 48 (49–54); total vertebrae 141 (140–142).
(dimensions in mm). Morphometric and meristic data are provided in Table
Meristic and morphometrics of Ariosoma gracile from Arabian Sea and Ariosoma kannani from the Gulf of Mannar, Bay of Bengal.
Ariosoma gracile sp. nov. | Ariosoma kannani sp. nov. | |||
---|---|---|---|---|
Holotype | Paratypes | Holotype | Paratypes | |
Total length (mm) | 241 | 197–221 (n = 4) | 173 | 157–201 (n = 2) |
%TL | ||||
Head length | 17.6 | 17.1–18.2 | 16.0 | 16.1 |
Depth at gill opening | 5.0 | 4.3–5.5 | 6.4 | 5.4–6.1 |
Depth at anus | 4.5 | 3.4–5.0 | 6.7 | 6.2–6.3 |
Width at anus | 3.6 | 3.2–4.0 | 4.9 | 4.7–4.9 |
Pre-dorsal length | 17.6 | 17.2–17.9 | 18.9 | 17.5–17.2 |
Pre-anal length | 43.7 | 41.3–44.7 | 46.9 | 46.0–47.2 |
Trunk length | 22.5 | 20.3–24.4 | 28.0 | 28.0–27.9 |
Tail length | 56.3 | 55.3–58.7 | 53.1 | 52.8–54.0 |
%HL | ||||
Snout length | 19.8 | 18.7–21.4 | 20.8 | 17.7–18.1 |
Eye diameter | 17.4 | 15.7–18.4 | 21.1 | 20.7–20.9 |
Interorbital width | 9.6 | 6.7–11.8 | 8.9 | 10.7–8.5 |
Upper jaw length | 29.5 | 27.6–31.8 | 29.5 | 23.7–28.5 |
Gill opening width | 15.4 | 10.4–18.0 | 12.8 | 10.0–10.8 |
Interbranchial width | 10.4 | 8.8–12.5 | 21.5 | 14.4–14.1 |
Pectoral-fin length | 32.9 | 26.8–36.9 | 37.0 | 29.5–37.4 |
Meristics | ||||
Pre-dorsal vertebrae | 9 | 9 | 10 | 10 |
Pre-anal vertebrae | 48 | 49–52 | 45 | 45–48 |
Total vertebrae | 141 | 140–142 | 116 | 118–116 |
Lateral-line pores | ||||
Pre-dorsal pores | 9 | 9 | 11 | 10 |
Pre-anal pores | 43 | 43–46 | 45 | 47 |
Total pores | 132 | 133–135 | 110 | 111–110 |
Body slender, cylindrical anterior portion, followed by more laterally compressed caudal portion; tip of caudal fin stiff and blunt or conical; anus positioned well-before mid-point of total length, pre-anal length 43.7% (41.3–44.7%) of TL; dorsal-fin origin above pectoral-fin base, above ninth lateral-line pores, confluent with caudal and anal fin. Origin of anal fin just after anus. Pectoral fin developed, with narrow base and pointed distally. Gill opening medium, slightly larger or equal to eye diameter, its upper origin reaching nearly upper half of pectoral-fin base; interbranchial width smaller than gill opening and eye diameter.
Head fairly large 5.9 (5.5–5.7) in TL, snout very short, anteriorly pointed in dorsal view, its length 1.1 (1.1–1.2) times eye diameter, projecting beyond lower jaw; length of snout relatively shorter than lower jaw; fleshy portion of snout projecting anteriorly beyond the end of intermaxillary tooth patch; rictus positioned just before middle length of eye. Fairly large tubular anterior nostril at tip of snout and relatively large elliptical pore of posterior nostril in front of mid-eye orbit diameter. Upper and lower jaw with slightly reduced flange. Tongue short and narrow; anterior portion free from mouth with conical or blunt tip.
Lateral-line pores complete; first pore commences moderately at level of supratemporal canal and terminating well before caudal-fin base; 9 (9) pre-dorsal pores; 43 (43–46) pre-anal pores and 132 (132–138) total pores.
Head pores moderate, few pores rather small. SO canal with 4 pores; first (ethmoidal) relatively small, on ventral side of snout tip; second pore medium-sized, in front of anterior nostril; third pore enlarged, on dorsal surface of snout just behind anterior nostril; fourth pore circular and enlarged, no pores in interorbital portion. IO canal with 8 (4+4) pores, first pore large, behind anterior nostril; second pore below posterior end of posterior nostril; third pore below anterior eye-orbit margin; fourth pore at above or slightly before rictus, below mid-eye; fifth pore behind rictus, at posterior margin of eye and 3 pores at infraorbital canal behind eye. POM pores 10; 7 in mandibular section, 6 before rictus and 1 behind rictus; pre-opercular section with 3 pores in a longitudinal row. Small-sized ST pores 0 or 3, (holotype and one paratype does not possess ST pores, 2 specimens with 3 pores and one specimen with 2 pores) (Fig.
Pre-dorsal vertebrae 9 (9); pre-anal vertebrae 48 (49–54); total vertebrae 141 (140–142).
Teeth larger, conical or pointed (no blunt teeth) (Fig.
(in fresh specimens). Body often bicolour, dark brownish to paler, upper half almost darker and paler ventrally; very minute dark pigmentations irregularly spread over body. Dorsal and anal fin creamy-white with thin black margin; caudal fin dull white with black upper and lower margins (Fig.
Known from five specimens collected from trawl by-catches landings at Kalamukku Fishing Harbour, off Kerala, south-western Indian coast, Arabian Sea, western Indian Ocean.
From the Latin word, ‘gracilis - gracile’ meaning slender, which denotes the slender-bodied eel.
Ariosoma gracile differs from all the congeners but shares similar morphological characters and overlapping pre-anal vertebrae counts with Ariosoma dolichopterum Karmovskaya, 2015 from the South China Sea, off Vietnam and Taiwan and Ariosoma emmae Smith & Ho, 2018 from Taiwan waters. Ariosoma gracile differs from these congeners by having: 132–135 total pores (vs. 121–129 in A. dolichopterum, 123–126 in A. emmae); 43–46 pre-anal pores (vs. 47–51 in A. dolichopterum, 50–53 in A. emmae); 9 pre-dorsal pores (vs. 5–9 in A. dolichopterum, 4–6 in A. emmae); more total vertebrae (140–142 vs. 129–134 in A. dolichopterum, 127–133 in A. emmae); trunk 38.5–42.6% TL (vs. 26.6–29.8% TL in A. dolichopterum, 28.9–32.7% TL in A. emmae); short vomerine tooth patch (vs. long in A. dolichopterum and A. emmae) (
Ariosoma gracile differs from the Indian water congeners, such as Ariosoma gnanadossi Talwar & Mukherjee, 1977, Ariosoma melanospilos Kodeeswaran, Jayakumar, Akash, Kumar & Lal, 2021, Ariosoma albimaculatum Kodeeswaran, Dhas, Kumar & Lal, 2022 and Ariosoma sp. nov.
The new species differs from the species viz. Ariosoma anago (Temminck & Schlegel, 1846), Ariosoma anale (Poey, 1860), Ariosoma fasciatum (Günther, 1872), Ariosoma meeki (Jordan & Snyder, 1900), Ariosoma howensis (McCulloch & Waite, 1916), Ariosoma shiroanago (Asano, 1958), Ariosoma coquettei Smith & Kanazawa, 1977, Ariosoma kapala (Castle, 1990), Ariosoma ophidiophthalmus Karmovskaya, 1991, Ariosoma multivertebratum Karmovskaya, 2004, Ariosoma sazonovi Karmovskaya, 2004, and Ariosoma sereti Karmovskaya, 2004 and in having fewer total vertebrae (140–142 vs. 143–144 in A. anago; 146–150 in A. anale; 155–158 in A. fasciatum; 144–155 in A. meeki; 151–161 in A. howensis; 161–162 in A. shiroanago; 152–160 in A. coquettei; 147 in A. kapala; 150–153 in A. ophidiophthalmus; 183–189 in A. multivertebratum; 146–148 in A. sazonovi; 168–172 in A. sereti; Ariosoma gracile differs from Ariosoma balearicum (Delaroche, 1809), Ariosoma megalops Fowler, 1938, Ariosoma scheelei (Strömman, 1896) and Ariosoma sokotranum Karmovskaya, 1991 in having more vertebrae (140–142 vs. 121–135 in A. balearicum; 114–118 in A. scheelei; 136–141 in A. sokotranum).
The specimens were directly preserved in formalin; hence this could not be included in the molecular analyses.
Holotype.
Paratype. EBRC/ZSI/F15710 (157 mm TL) taken with holotype, EBRC/ZSI/F15711 (201 mm TL) , Shankarpur Fish Landing Centre, West Bengal, Coll. Dipanjan Ray, 10 November, 2021.
A small-sized slender eel species of Ariosoma distinguished from all other species by the following combination of the characters: dorsal-fin origin behind pectoral-fin insertion, pre-anal length 46.0–47.2% of TL, smaller eye, 20.7–21.1% HL, smaller interorbital distance, 8.9–10.7% HL, no distinct bands on head, pre-opercle whitish, teeth on jaw small, pointed, intermaxillary and vomerine teeth continuous, short vomerine tooth patch; SO canal with 6 pores; 3 pores on ST canal; pre-dorsal vertebrae 10 (10); pre-anal vertebrae 45 (45); total vertebrae 116 (118).
Body stout, anterior portion cylindrical, laterally compressed in tail region; caudal fin tip rounded; anus positioned at mid-point of body, pre-anal length 46.0–47.2% of TL; dorsal-fin origin behind pectoral-fin insertion, above tenth to eleventh lateral-line pores. Pectoral-fin developed, with a narrow base and round or blunt distally. Gill opening small, smaller than eye diameter, interbranchial width larger than gill opening and smaller than eye diameter.
Head moderately large 6.0 (5.5) in TL, snout short, anteriorly pointed in dorsal view, its length 1.1 times eye diameter, projecting beyond lower jaw; snout length shorter than lower jaw; fleshy portion of snout projecting anteriorly beyond the end of intermaxillary tooth patch; rictus positioned just behind middle length of eye. Tubular anterior nostril moderate in size at snout tip and posterior nostril relatively large elliptical pore, in front of mid-eye orbit diameter. Upper and lower jaw with reduced flange.
Lateral-line pores complete; first pore commences at level of supratemporal canal and terminates well before base of caudal fin; 10–11 pre-dorsal pores; 45–47 pre-anal pores and 110–111 total pores.
Head pores medium or small. SO canal pores 6; first pore (ethmoidal) smaller, on snout tip; second pore medium, just before anterior nostril; third pore enlarged, on dorsal surface of snout just behind anterior nostril; fourth pore moderate, behind posterior nostril; fifth pore smaller, at anterior interorbital space; sixth pore small at posterior interorbital space. IO canal pores 8 (4+4), first pore moderate, behind anterior nostril; second pore below posterior nostril; third pore below just before orbit eye-orbit margin; fourth pore at slightly before rictus, fifth pore behind rictus and 3 pores at infraorbital canal behind eye. POM pores 10; mandibular section with 7, pre-opercular section with 3 pores in a longitudinal row. ST pores 3, 1 median pore and 1 lateral pore on each side just behind median pore (Fig.
Teeth on jaws small, pointed; continuous maxillary and intermaxillary teeth; intermaxillary and vomerine teeth continuous; vomerine teeth pointed anteriorly and blunt posteriorly, reach beyond mid-maxillary teeth row (Fig.
Pre-dorsal vertebrae 10, pre-anal vertebrae 45–48; total vertebrae 116–118.
Dorsal body pale brownish; ventral half above anus whitish; dorsal fin margin black; anal fin clear; pre-opercle whitish; head brownish; interorbital region black; pectoral-fin translucent; ventral surface of lower jaw whitish without any black pigmentation (Fig.
Indian Ocean: Gulf of Mannar, Bay of Bengal probably widespread in the east coast of India, but rare in catch.
The species was named after the late Prof. Dr. L. Kannan, Former Director, CAS in Marine Biology, Annamalai University and Former Vice Chancellor, Thiruvalluvar University for his contribution in Marine Science.
Ariosoma kannani is closely related to Ariosoma megalops from China, Taiwan and Vietnam waters in having the dorsal-fin origin behind the pectoral-fin insertion and similar vertebral counts, but the new species readily differs by having smaller interorbital distance (8.9–10.7% HL vs. 12.1–18.4% HL in A. megalops) and smaller mean eye diameter (20.9% HL vs. 22.8–22.9% HL) and the new species show 10.8% genetic divergence from A. megalops from the Taiwan waters. The new species shares similar vertebral counts with Ariosoma scheelei, a widely distributed species in Indo-West Pacific, but A. kannani can be easily distinguished from A. scheelei by having fewer POM pores (10 vs. 12 in A. scheelei) (
Out of 548 bp studied, conserved and variable sites were found to be 348 bp, 200 bp long, respectively. Amongst variable sites, parsimony informative sites constitute 190 bp, wherein a singleton with 10 bp. The nucleotide composition was found to be A = 26.1%; T = 30%; C = 25.2%; G = 18.7. The transition and transversion bias (R) was documented using substitution patterns and rates were ascertained using the Kimura 2 Parameter model. The obtained R value of 7.48, clearly indicate the sequences of the species used for analyses are delineated in a proper manner. The R value supports the findings of genetic divergence values and phylogenetic tree analyses.
The Maximum Likelihood tree (Fig.
Maximum Likelihood phylogeny tree of the genus Ariosoma from analysis of cytochrome c oxidase subunit I gene, including new species, Ariosoma kannani collected from the south Indian coast, based on the IQ-Tree. The ML tree was plotted with the HKY+F+I+G4 model using ModelFinder (
At present, 40 species of the genus Ariosoma were described (
The phylogenetic analyses of this study was based on only one marker due to availability of comparative sequences in public domain. Phylogenetic analyses for most of the species of the genus Ariosoma was meagre, hence vast sampling is needed to fulfil the complete genomics of these congrid eel groups. Furthermore, most eels do not possess economic value and are landed mostly as by-catch and sampling on this group was very rare in Indian waters (
PK collected, identified, examined the specimens and prepared the manuscript. PK and AK performed molecular analyses and revised the manuscript. AM identified, examined the specimens and revised the manuscript. DR collected and identified specimens from West Bengal. TTA and CR revised the manuscript. UKS provided comprehensive guidance and supported the work. All authors read and approved the final version of the manuscript.
The authors acknowledge the Director, ICAR–National Bureau of Fish Genetic Resources (