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Discovery of a ribbon goby, Oxymetopon compressus (Actinopterygii: Gobiiformes: Microdesmidae) in Indian waters: A new westernmost record for the genus Oxymetopon
expand article infoSivakumar Ragul‡, Gopalan Mahadevan‡, Arumugam Murugan§, Ronald Fricke|
‡ Annamalai University, Cuddalore, India
§ Crab Meat Processors Association, Tuticorin, India
| Staatliches Museum für Naturkunde in Stuttgart, Stuttgart, Germany

Corresponding author: Gopalan Mahadevan ( marinemahadevan@gmail.com )

Academic editor: Adnan Tokaç
© 2024 Sivakumar Ragul, Gopalan Mahadevan, Arumugam Murugan, Ronald Fricke.
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: Ragul S, Mahadevan G, Murugan A, Fricke R (2024) Discovery of a ribbon goby, Oxymetopon compressus (Actinopterygii: Gobiiformes: Microdesmidae) in Indian waters: A new westernmost record for the genus Oxymetopon. Acta Ichthyologica et Piscatoria 54: 125-129. https://doi.org/10.3897/aiep.54.118272
ZooBank: urn:lsid:zoobank.org:pub:E79B865C-14D7-4D00-9070-60F5DAD5CDE9
Open Access

Abstract

In October 2023, a single specimen of Oxymetopon compressus Chan, 1966 was retrieved from a discarded catch at the Mudasal Odai fish landing center on the southeast coast of India. This study marks the first record of the genus Oxymetopon in Indian waters, accompanied by a novel maximum length record. Oxymetopon compressus, closely resembles its congener, Oxymetopon formosum Fourmanoir, 1967 in having low supraorbital crest and head markings, but differs in having relatively a higher number of anal fin rays, 29 (vs. 27 in O. formosum). The anal fin count of O. compressus (29) is found higher than the Oxymetopon curticauda Prokofiev, 2016 (21–23) and Oxymetopon filamentosum Fourmanoir, 1967 (26), whereas it is found lower than the Oxymetopon cyanoctenosum Klausewitz et Condé, 1981 and Oxymetopon typus Bleeker, 1861 (31). This study describes the distinctive morphological and coloration patterns of the recorded species.

Keywords

Bay of Bengal, distribution, Microdesmidae, new record, ribbon goby

Introduction

The family Microdesmidae, commonly known as wormfish, comprises two subfamilies: Microdesminae and Ptereleotrinae. Within the subfamily Ptereleotrinae, there are eight valid genera and 64 valid species (Fricke et al. 2023). The western Pacific genus Oxymetopon Bleeker, 1861 accommodates six valid species (Chan 1966; Fourmanoir 1967; Klausewitz and Condé 1981; Prokofiev 2016): Oxymetopon compressus Chan, 1966; Oxymetopon curticauda Prokofiev, 2016; Oxymetopon cyanoctenosum Klausewitz et Condé, 1981; Oxymetopon filamentosum Fourmanoir, 1967; Oxymetopon formosum Fourmanoir, 1967; and Oxymetopon typus Bleeker, 1861.

Ribbon gobies are predominantly found in silty mud burrows (Klausewitz and Condé 1981; Prokofiev 2016). This study focuses on presenting a novel westernmost distribution record of a ribbon goby species, Oxymetopon compressus, in Indian waters, accompanied by a detailed analysis of its morphology, meristic features, and color patterns. One of the newly recorded specimens represents a new maximum length record (94 mm standard length).

Materials and methods

The specimens examined in this study were obtained through monthly trawl bycatch surveys conducted along the southern region of the east coast of India. Mudasal Odai, a prominent fish landing center on India’s southeastern coast, was selected for its rich diversity in discarded catches, warranting a comprehensive study (Murugan et al. 2023; Ragul et al. 2024). In October 2023, a single specimen of a gobiid fish representing the genus Oxymetopon was identified within the trawl bycatch at the fish landing center in Mudasal Odai (11°29′06″N, 079°46′28″E).

Measurements were conducted using a Mitutoyo CD-6”ASX digital caliper, ensuring a precision of 0.1 mm. Morphometric and meristic characters were documented following Hubbs and Lagler (1964). The collected specimens were preserved in 10% formaldehyde and are housed in the reference museum of the Centre of Advanced Studies in Marine Biology, Annamalai University (CASMBAURM), India.

Identification of the presently reported specimen up to the species level was carried out with reference to Chan (1966), Klausewitz and Condé (1981), and Prokofiev (2016). Family-group classification followed van der Laan et al. (2014), while the genus and species classifications followed Fricke et al. (2023).

Results

Systematic position

Order Gobiiformes

Family Microdesmidae Regan, 1912

Subfamily Ptereleotrinae Bleeker, 1875

Genus Oxymetopon Bleeker, 1860

Oxymetopon compressus Chan, 1966

English common name: robust ribbon goby Fig. 1A–1E; Table 1

Oxymetopon compressus.—Chan (1966): pp. 1–3, fig. 1.—Klausewitz and Condé (1981): pp. 67–76, figs. 5, 5a, 6, 7, 19b, tables I and III.—Koeda and Ho (2019): pp. 85–87.

Oxymetopon compressum.—Prokofiev (2016): pp 175–180, figs. 1c, 2c, table 1 and 2.—Prokofiev (2020): pp. 115, 116, fig. 1f.

Material examined

CASMBAURM/2312819, 1 probably female, 94 mm SL (Fig. 1A–1E), southeast coast of India, off Parangipettai, Mudasal Odai (fish landing center); 11°29′06″N, 079°46′28″E; 9 Oct. 2023, S. Ragul leg.

Figure 1. 

Oxymetopon compressus (CASMBAURM 2312819) from southeastern India: (A–C) lateral view of (A) fresh, (B) preserved specimen, and (C) radiograph; (D and E) lateral view of head: (D) prominent bright bands and red high crest; (E) prominent small scales and canine teeth. Scales: A and B = 10 mm; D and E = 5 mm.

Description

First dorsal spines VI; second dorsal fin elements I + 29; anal rays I + 29, pelvic rays I + 4; pectoral rays 19; caudal rays 20; predorsal scales 21; gill rakers on 1st arch 26. Meristics and morphometrics in Table 1. Body elongate, laterally compressed, maximum depth (below first dorsal fin) 19.1% of SL, caudal-peduncle depth 9.7% of SL. Straight frontal profile, upward faced lower and upper jaws, 46.0% and 41.5% in HL respectively. A distinct frontal notch present before eye. High dorsal crest (fleshy keel) present. A pair of nasal openings in preorbital region. Mouth oblique, with a single outer row of small, irregular, slightly curved, inward-pointed canine teeth on premaxillary (Fig. 1E). Branchiostegal rays 5/5. Body with small soft ctenoid scales, nape with cycloid scales. Caudal-fin base completely covered with scales. First dorsal fin low (base length 14.5% of SL), second ray 13.5% of SL, connected with second dorsal fin by a low membrane. Second dorsal fin (base length 49.4% of SL) with fourth ray 10.8% of SL; anal fin (base length 42.5% of SL) with third ray 9.2% of SL. Caudal fin lanceolate, pointed, caudal-fin length 30.3% of SL. Pectoral fin rounded, its length 13.6% of SL. Pelvic fin with third ray elongate, pelvic-fin length 14.0% of SL.

Table 1.
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Morphometric and meristic data of Oxymetopon compressus from Mudasal Odai, India, compared with type specimen.

Character Chan 1966 Prokofiev 2016 This study
Holotype Hong Kong Vietnam southeastern India
n = 1 n = 12 n = 1
Measurements (absolute values) [mm]
Total length (TL) — — 124
Standard length (SL) 66.4 57–82 94
Head length (HL) 12.6 — 14.0
Measurements (relative values) [% of SL]
Head length 18.9 15.9–20.2 (18.2) 14.9
Greatest body depth at hind base of first dorsal 22.3 17.4–19.3 (18.3) 19.1
Caudal-peduncle depth 11.3 9.1–11.0 (10.2) 9.7
Predorsal (1) length 24.1 — 21.2
Predorsal (2) length 45.2 — 42.2
Preanal length 51.2 — 46.2
Prepectoral length 20.2 — 17.9
Prepelvic length 26.2 — 21.9
Length of first dorsal-fin base 13.6 — 14.5
Length of second ray of first dorsal fin 12.0 — 13.5
Length of second dorsal-fin base 46.7 — 49.4
Length of fourth ray of second dorsal fin 13.6 — 10.8
Length of anal-fin base 41.9 — 42.5
Length of third ray of anal fin 9.0 — 9.22
Pectoral-fin length 18.1 16.3–20.8 (17.9) 13.6
Pelvic-fin length 17.3 14.6–17.5 (16.0) 14.0
Caudal-fin length 37.7 — 30.3
Measurements (relative values) [% of HL]
Eye diameter 31.8 — 31.2
Upper-jaw length 43.7 — 41.5
Snout length 22.2 — 17.3
Interorbital width 22.2 — 21.1
Counts
First dorsal-fin elements VI VI VI
Second dorsal-fin elements I, 30 I, 27–30 I, 29
Anal-fin elements I, 29 I, 26–29 I, 29
Pectoral-fin rays 20 18–21 19
Pelvic-fin rays I, 4 I, 4 I, 4
Caudal-fin rays 20 — 20
Predorsal scales 31 — 31
Gill rakers on first arch 32 27–28 (6–7) 32
Vertebral formula — 10 + 16 10 + 16

Coloration

Freshly dead specimen (Fig. 1A): Head and body pinkish brown; distinct red blotch on upper base of pectoral fin; crest rimmed with bright red; eye with red blotch each on upper and lower margins (Fig. 1D). Three grey-blue iridescent bars traversing eye. Anal fin and lower caudal fin light reddish pink; caudal fin with vertical light orange and pale blue bars. In preserved specimen (Fig. 1B), head and body transitioning to yellowish tint, and belly partially whitish. Anal fin darker compared to fresh state, and caudal fin with prominent dark vertical lines.

Habitat

The robust ribbon goby, Oxymetopon compressus, has been reported from a depth range of 10 to 18 m, predominantly on silty-sand bottoms, positioned at the outer edge of coral reefs (Prokofiev 2016). The type specimen, as documented by Chan (1966), was collected on a muddy bottom within the depth range of 14 to 16 m.

In contrast, the presently reported specimen was discovered in a novel habitat, ranging from 20 to 25 m in depth. This new location features muddy-silt washed-out bottom sediments along the Parangipettai coast.

Distribution

Oxymetopon compressus has been known only from the western Pacific, from Hong Kong (Chan 1966), Japan: Okinawa, Ryukyu Islands (Ikeda et al. 2000; Akihito et al. 2002), Gulf of Thailand, East Sumatra, Papua New Guinea, Australia: Low Isles, Queensland (Allen and Erdmann 2012) and Vietnam (Prokofiev 2016). The presently reported study expands its distribution to the southeast coast of India in the Indian Ocean.

Discussion

The robust ribbon goby, Oxymetopon compressus, differs from its congeners by the number of dorsal-fin rays and anal-fin rays, especially by the length of the pelvic and pectoral fins and by their color characters. It is distinguished from O. filamentosum and O. typus by its relatively short first dorsal spines (vs. filamentous in O. filamentosum and long in O. typus) and by having the anal fin elements of I + 29 (vs. I + 26 in O. filamentosum and I + 31 in O. typus).

Oxymetopon compressus differs from O. curticauda by having a higher number of dorsal and anal fin elements of I + 29 (vs. I + 22–23 and I + 21–23 in O. curticauda). O. compressus differs from O. cyanoctenosum with a more gill rakers count in first gill arch 26 (vs. 21 in O. cyanoctenosum) and comparatively length of the pelvic fin is slightly longer than the length pectoral fin but not reaching the anus (vs. elongated pelvic fin which reaches the anus in O. cyanoctenosum).

Oxymetopon compressus is most similar to O. formosum in sharing low supraorbital crest and head markings (Klausewitz and Condé 1981). However, O. compressus differs in the presence of anal fin elements I + 29 (vs. I + 27 in O. formosum).

The new record from southern India expands the distribution range of the species by approximately 2200 km to the west (Fig. 2). It indicates that this rare species is apparently much more widespread than previously known and is also expected to occur in the intermediate regions. Additional studies of silty or muddy sediments in the eastern Indian Ocean and western Pacific are needed to assess the full distribution range of O. compressus.

Figure 2. 

Distribution range of Oxymetopon compressus. A = new record; B = type locality; C = other records.

Acknowledgments

The authors are grateful to the Director and Dean of the Faculty of Marine Sciences, Annamalai University, for providing facilities enabling this research. The authors are obliged to Dr Helen K Larson, Museum and Art Gallery of the Northern Territory, Australia for her help in confirming the identification of this species. The authors would also like to thank Mr M. Subramaniyan and Dr M. Divya Sneha for their help in the radiograph of the fish specimen. The authors wish to extend their sincere gratitude to the reviewers for their valuable comments.

References

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