Introduction
Gobiidae (Perciformes, Gobioidei) are the most diverse group of marine teleost fishes, well represented in marine, brackish, and freshwater habitats (Eschmeyer et al., Reference Eschmeyer, Fricke, Fong and Polack2010; Larson et al., Reference Larson, Heemstra, Heemstra, Ebert, Holleman and Randall2022a, Reference Larson, Murugan, Ragul and Mahadevan2022b) with well over 2000 extant species currently recognized (Fricke et al., Reference Fricke, Eschmeyer and Van Der Laan2023). The Indo-Pacific gobiid genus Acentrogobius Bleeker 1874 typically inhabits soft substrata of coastal bays, mangrove streams, estuaries, and freshwater (Allen et al., Reference Allen, Erdmann and Hadiaty2015). Allen (Reference Allen2015) discussed some taxonomic problems associated with this group, which Larson and Lim (Reference Larson and Lim2005) referred to as a confusing group and a ‘catch basket’ for many gobies of similar appearance. A total of 25 valid species have been described under this genus worldwide (Fricke et al., Reference Fricke, Eschmeyer and Van Der Laan2023). In India, a number of species of Acentrogobius and its close relatives (Amoya, Aulopareia, Yongeichthys) have been reported, under a variety of names; work on this group remains to be done.
The tridentigerine genus Pseudogobius comprises 15 valid species which inhabit marine, estuarine to fresh waters (Larson, Reference Larson2001; Larson and Hammer, Reference Larson and Hammer2021). In India, two species of this genus have been reported, namely P. melanosticta (Day, 1876) and P. minimus (Hora, 1923), with other records being misidentifications. Pseudogobius fulvicaudus Huang et al. (Reference Huang, Shao, Huang, Chong and Chen2014), commonly known as Yellowfin snubnose goby, is so far known from the waters of Brunei, Malaysia, Northern Australia, Vietnam, Singapore, and Thailand (Larson and Hammer, Reference Larson and Hammer2021).
During recent monthly fish surveys conducted along the estuaries and fish landing centres of Tamil Nadu coast, Southeast India, from April 2021 to June 2023, we recorded the above two species for the first time from Indian waters.
Methods
The present specimens were collected at regular weekly intervals for a period of two years from April 2021 to June 2023 along the estuaries and fish landing centres of Tamil Nadu coast, Southeast India, to document estuarine cryptic species, trawl bycatch species, and their diversity. Four specimens of P. fulvicaudus were collected during this study from the Ennore estuary (13°13′24″N 80°18′57″E) and Vellar estuary (11°29′26″N 79°45′58″E) which are lined with mangroves (Figure 1). The specimens were collected by using scoop net and by hand-picking methods during the receding period of the incoming tides. Five specimens of A. vanderloosi were collected from the bycatch of bottom trawlers targeting non-penaeid shrimp (mesh size range, 20–40 mm) at Mudasal Odai (11°29′06″N 79°46′28″E) and Pazhayar (11°21′32″N, 79°49′22″E) (Figure 1) fish landing centres. Trawling was carried out nearshore at depths ranging from 10 to 15 m, at a distance of 1–10 km from the shore.
Figure 1. Map representing present sampling points. Acentrogobius vanderloosi (red): Mudasal Odai fishing harbour (Red circle), Pazhayar fish landing centre (red square); Pseudogobius fulvicaudus (yellow): Ennore estuary (Yellow circle), and Vellar estuary (yellow square).
After collection, the specimens were cleaned from mucus, debris, and mud prior to fixation and fresh photographs were taken. The meristic counts were noted, and morphometric characters were measured using Mitutoyo CD-6”ASX® digital Vernier calliper with the nearest 0.1 mm accuracy. Later, the specimens were preserved in 10% formaldehyde and then into 70% ethanol (R). specimens were identified using Allen (Reference Allen2015) and Larson and Hammer (Reference Larson and Hammer2021) and measured as per Hubbs and Lagler (Reference Hubbs and Lagler1958). Specimens examined are deposited in the Centre of Advanced Studies in Marine Biology, Faculty of Marine Sciences, Annamalai University, Reference Museum (CASMBAURM), Parangipettai, India.
Results
Systematics
Family Gobiidae Cuvier, 1816
Subfamily Gobiinae Cuvier, 1816
Genus Acentrogobius Bleeker, 1874
Acentrogobius vanderloosi Allen, Reference Allen2015
(Figure 2 & Table 1)
Materials examined
One female specimen (CASMBAURM/2312711), 85.79 mm SL, from Pazhayar fish landing centre (11°21′32″N, 79°49′22″E), coll. A. Murugan, June 2021. 1 female specimen (CASMBAURM/2312712), with SL of 79.88 mm, June 2022; 1 male and 2 female specimens (CASMBAURM/2312713–15), 69.72–89.85 mm SL, June 2023 from Mudasal Odai fish landing centre (11°29′06″N 79°46′28″E), India: Tamil Nadu, coll. S. Ragul.
Figure 2. Fresh coloration of Acentrogobius vanderloosi (85.79 mm SL) from Pazhayar fish landing centre, Southeast coast of India: Tamil Nadu (scale 10 mm). Photo by A. Murugan.
Table 1. Morphometric and meristic data for Acentrogobius vanderloosi Allen, Reference Allen2015 (Mudasal Odai, India) compared to data from type specimens (Allen, Reference Allen2015)
Additional material observed
Larson and Murugan collected this species on 2 August 2018 at Pazhayar fish landing, Tamil Nadu (specimens not retained). During 2008–2012, Sedeepta Biswas, Ravi Velayudham, and Dijpanan Ray have sent Helen K. Larson, photos of this species collected from Northeast and Southeast coast of India.
Diagnosis
Dorsal-fin rays VI + I,10; anal-fin rays I,10; pectoral-fin rays 20; caudal fin pointed; longitudinal scale series 30; transverse-scales 9–10; predorsal-scales 12–13; body covered with ctenoid scales, cycloid on breast, pectoral-fin base and head; uppermost portion of opercle with three scale rows; and scaled cheek (Allen, Reference Allen2015).
Description
Dorsal-fin rays VI + I, 10; anal-fin rays I, 10; pectoral-fin rays 20; pelvic-fin rays I, 5; segmented caudal-fin rays 18 (17–18); longitudinal scale series 31(30–31); transverse scales 10 (9–11); predorsal scales 12 (11–13); and circumpeduncular scales 12 (12–13). Body elongate, compressed laterally; body depth at pelvic-fin base 19.73–20.89% SL and body depth at anal origin 19.73–20.89% of SL; head length 25.87–27.04% of SL. Body scales ctenoid up to pectoral fin base, predorsal with cycloid scales; pectoral fin base naked, belly scales cycloid; distance between snout and origin of first dorsal fin 30.41–33.14 in % of SL, between snout and origin of second dorsal fin 54.4–56.17, between snout and origin of anal fin 56.61–57.92, between snout and origin of pelvic fins 29.28–31.81, and between snout and origin of pectoral fin 25.51–28.2 all in % of SL. Caudal peduncle slender with length of 15.13–18.09% of SL and with compressed width of 4.09–4.58% of SL and caudal peduncle depth 10.65–11.04% of SL.
Head rounded and wide, width at the posterior preopercular margin 15.86–16.08% of SL. Head depth at posterior preopercular margin 16.14–16.68% of SL. Opercle with 1–3 rows of cycloid scales, fully scaled cheek (i.e. preopercle) with depth of 7.86–8.34% of SL; and belly scales cycloid. Snout rounded and contributing 6.71–6.96% of SL. Eyes large, diameter width 6.87–7.72% of SL. Terminal mouth, jaws reaching to a vertical below mid-eye region, upper jaw length 8.19–9.53% of SL. Maxilla extending up to vertical anterior margin of the eye. Small teeth in jaws, with several rows of posteriorly curved canine teeth: a pair at upper jaw and a single row at lower jaw. Bilobed broad tongue. Gill-opening extending anteriorly up to below mid-preopercle. Triangular first dorsal fin with second spine longest (34.29–37.92% of SL), with first spine (36.29–36.57% of SL), and third (25.46–28.74% of SL). Correspondingly, the length of second dorsal fin base (35.12–37.45% of SL) is greater than the first dorsal base (10.37–12.88% of SL). Oval shaped pectoral and pelvic fins with length of 23.88–24.55% of SL and 19.59–22.27% of SL; pelvic fin spine length 6.47–8.03% of SL; Short anal fin with base length of 25.6–26.67% of SL; narrow caudal fin with tapered point, 26.85–28.18% of SL (Table 1).
Coloration (live specimen) (Figure 2), pale grey with rows of orange spots on body; five horizontally-elongate to rounded brown blotches on midline of the body, 5th and darkest blotch located at middle of caudal-fin base, two orange stripes on cheek and pale blue short stripe under eye and a variably sized bluish blotch on opercle; pectoral fin base with two orange bars extending close to ray bases; unpaired fins with rows of orange spots or short lines.
Coloration (preserved specimen), body becomes paler than the live specimen, brown blotches become into dark black blotches, the pair of orange stripes become paler into whitish stripes, and the blue spot on the opercle remains bright.
Distribution. This species was previously known from the type locality of Alotau, Milne Bay Province, Papua New Guinea (Allen, Reference Allen2015; Figure 4).
Remarks
Acentrogobius vanderloosi belongs to the Yongeichthys species-group (see Larson in Heemstra et al., Reference Larson, Heemstra, Heemstra, Ebert, Holleman and Randall2022a) in having longitudinal rows of sensory papillae on the cheek, the gill opening extending forward to mid-preopercle, and a single transverse row of papillae on the chin (the Acentrogobius species-group has two groups of transverse papilla lines on the chin).
It differs from its congeners by having 10 anal-fin rays, 20 pectoral fin rays, both the cheek and opercle completely scaled, and having all first dorsal fin spines greatly elongate and filamentous. The colour pattern of A. vanderloosi is diagnostic, particularly the combination of a pair of yellow cheek stripes, numerous orange spots on the body, and the lack of parallel dark stripes on the side that enclose the large dark marks along the side in other Acentrogobius (Allen, Reference Allen2015).
Systematics
Family Gobiidae Cuvier, 1816
Subfamily Gobionellinae Bleeker, 1874
Genus Pseudogobius Popta, 1922
Pseudogobius fulvicaudus Huang et al., Reference Huang, Shao, Huang, Chong and Chen2014
(Figure 3 & Table 2)
Figure 3. Live coloration of Pseudogobius fulvicaudus (17.9 mm SL) from Ennore estuary, Southeast coast of India: Tamil Nadu (scale 5 mm). Photo by Aravind Manoj.
Table 2. Morphometric and meristic data for female P. fulvicaudus (Ennore and Vellar estuary, India) compared to data of female type specimens Huang et al. (Reference Huang, Shao, Huang, Chong and Chen2014); Larson and Hammer (Reference Larson and Hammer2021)
Materials examined
Two females (CASMBAURM/2312624–25), 14.2–15.3 mm SL, from Ennore mangrove forest (13°13′24″N 80°18′57″E), coll. Aravind Manoj, July 2021. One male and 1 female specimen (CASMBAURM/2312626–27), 14.8–17.9 mm SL from Vellar mangroves forest (11°29′26″N 79°45′58″E) and Parangipettai, coll. S. Ragul, April 2022; Southeast India: Tamil Nadu.
Diagnosis
Both second dorsal-fin rays and anal-fin rays I, 6–9; pectoral-fin rays 14–17; segmented caudal fin rays 16; lateral scale series 24–30; cheek scales behind eye 1–3; opercle partially scaled; and predorsal scales 6–11 (Larson and Hammer, Reference Larson and Hammer2021).
Description
Body slender, anteriorly sub-cylindrical and posteriorly compressed. Body depth at anal origin 15.0–16.1% of SL. Caudal peduncle slender and compressed, 28.4–29.5% of SL and caudal peduncle depth 11.7–11.9% of SL. Ctenoid scales over body up to pectoral fin base, cycloid scales over predorsal; naked pectoral fin base, and belly scales cycloid.
Head appears rounded and wide, width at posterior preopercular margin 70.9–74.5% of HL; depth from 53.2 to 59.1% of HL. 1–3 cycloid scales rows on opercle, cheek appears scaleless; and scales on ventral region cycloid. Snout rounded and slightly inflated, length 16.1–16.4% of HL. Eyes large, diameter 31.7–33.4% of HL. Interorbital region moderately wide, 15.6–18.9% of HL. Mouth small and terminal, slightly oblique, jaws reaching back to below mid-eye with upper jaw length 26.7–32.2% of HL. Anterior nostril in short tube and oval to round shaped posterior nostril opening. Two rows of upper and lower jaw teeth. Short and blunt tongue tip. Gill-opening extending ventrally up to below middle of opercle. Very diminutive gill rakers on outer face of first gill arch (Table 2).
Short triangular shaped first dorsal fin with rounded margin, second spine longer than other spines. Pectoral fin oval, pelvic fin narrow and oval, short anal fin, and round caudal fin.
Coloration (live, Figure 3). Head and body translucent, whitish ventrally. Oblique blackish brown bar extends below rear part of first dorsal fin base halfway down side of body; above the anal fin, two internal blackish ventral spots and two on caudal peduncle. First dorsal fin with rounded black mark posteriorly close to fin base, covering fifth to sixth spines and a yellow bar above the black mark covering second to fourth spines. Scattered dusky grey irregular small spots on cheek and opercle; outer rim of the eye golden. Eye golden brown, opercle with pale blue patch. Base of pectoral fin with dusky grey spots. Caudal fin with two blackish rounded spots, usually larger spot at lowermost caudal base, darker than upper and not in contact with diffuse grey mid-base spot; a broad half-moon yellow band extends out from fin base onto caudal fin. Transparent to faintly grey second dorsal fin with diffuse yellow area on lower part, clear to whitish fin margin. Translucent whitish to translucent yellow anal fin. Transparent pectoral fin. Translucent pelvic fins to whitish.
Coloration (preserved material)
Similar to live colour, but yellow colour fades to pale brown.
Habitat and distribution
Intertidal muddy areas and shallow tidal pools of mangroves are where this species has previously been recorded in Brunei, Malaysia, Northern Australia, Vietnam, Singapore, and Thailand (Larson and Hammer, Reference Larson and Hammer2021; Figure 4).
Figure 4. Distribution range of Acentrogobius vanderloosi (red) and Pseudogobius fulvicaudus (black): present study area (star), type localities (square), and previously known localities (circle) from literature and specimens in collections.
Remarks
Pseudogobius fulvicaudus, differs from its congeners by the following characters: caudal fin base with distinct two black spots. A prominent bright yellow, semicircular to vertical band on anterior part of caudal fin.
Discussion
This paper presents the first records of A. vanderloosi and P. fulvicaudus from Indian waters and extends its distributional range considerably. Allen and Erdmann (Reference Allen and Erdmann2012) commented that Acentrogobius (Bleeker) genus contains a diversity of morphological forms and is most likely a polyphyletic assemblage.
Pseudogobius fulvicaudus co-occurs with Acentrogobius audax, A. viganensis, A. viridipunctatus, Favonigobius reichei, Psammogobius biocellatus, Hemigobius hoevenii, Eugnathogobius mindora, Mugilogobius tigrinus, Pseudogobius minimus, and P. melanostictus from shallow intertidal muddy habitat of Ennore mangroves and edible oyster beds of Vellar mangrove forest. These types of habitats are common along the Indian coast which likely harbour a greater diversity of gobioids. Larson and Hammer (Reference Larson and Hammer2021) commented that preliminary DNA analyses shows that P. fulvicaudus is likely to be a species-complex, so additional genetic and morphological work is required on the Indian populations to understand this.
Conclusion
The records of these species of Acentrogobius and Pseudogobius from Tamil Nadu coastal waters are new additions to the list of marine and estuarine fishes of Indian coastal waters as well as drawing attention to the problems in identification of the gobioid fishes of India. It is a well-known fact that coastal areas are utilized for various infrastructure projects and human settlements and linked activities. Due to these developmental activities, gobioid fishes as a whole will be facing problems at present and in the near future. Hence it is very important to document these coastal dwelling fishes at the earliest, so that the coastal impacts can be evaluated on biodiversity as soon as possible.
Acknowledgements
The authors are thankful to the Director and Dean of the Faculty of Marine Sciences, Annamalai University, for providing necessary facilities.
Data Availability Statement
All relevant dataset supporting the conclusions of this article is included within the article.
Author contributions
S.R. and G.M. wrote the first version of the manuscript. A.M. and S.R. carried out field sampling and collected the specimens. All authors contributed to the draft, provided critical feedback and helped shape the research. All authors read and approved the final manuscript.
Financial support
This research received no specific grant from any funding agency, commercial or not-for- profit sectors.
Competing interest
None.
Ethical standards
Not applicable.
