Acanthopagrus datnia
Creators: name: Hasan, Mohammad Eusuf
name: Durand, Jean-Dominique
name: Iwatsuki, Yukio
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Perciformes
Sparidae
Acanthopagrus
Acanthopagrus datnia

description: Acanthopagrus datnia (Hamilton, 1822)
(Figures 1, 5–8, 10–11, 12A, 13A & Table 2)
Bengal Yellowfin Seabream
Coius datnia Hamilton, 1822: 88, 369, pl. 9, fig. 29 (type locality: Ganges River mouths, Bengal, British India, no type known).
Datnia Buchanani Cuvier, 1829: 148 (unneeded replacement name for Coius datnia Hamilton, 1822).
Chrysophrys longispinnis Valenciennes in Cuvier & Valenciennes, 1830: 116 (type locality: Bengal, India; and Japan; in part, Bengal specimens only); Bleeker 1853: 93 (Bengal, India and Japan; in part, Bengal specimens only); Bauchot & Daget 1972: 46 (Bengal, India and Japan; in part, Bengal specimens only); Bauchot & Skelton 1986: 331 (Bengal, India and Japan; in part, Bengal specimens only).
Chrysophrys hasta (not of Bloch & Schneider); Günther 1859: 490 (in part, Bay of Bengal specimens with 12 dorsal-fin spines, entering rivers).
Pagrus flavipinnis (invalid name); Günther 1859: 490 (name in text, Bay of Bengal).
Sparus datnia; Bleeker 1877: 5 (in part, Bengal specimen only); Hora & Mukerji 1936: 18 (Rangoon, Myanmar, list only); Misra 1959: 278 (in part, Chennai [= Madras], Orissa and West Bengal, India specimens only).
Chrysophrys datnia; Day 1876: 140, plate 34-1(Hooghly Estuary at Calcutta, Bengal, India); Day 1889: 44 (estuaries of eastern India); Lloyd 1907: 228 (Akyab, Myanmar; list only).
Mylio latus; Munro 1949: 203 (Bay of Bengal specimen only); Eggleston 1974: SPARID Myl 2 (Bay of Bengal specimen only).
Acanthopagrus datnia; Hussain 1969: 45 (estuarine waters of Bangladesh, list only); Rahman 1974: 17 (tidal rivers of Bangladesh, list only); Rahman 1989: 327 (tidal rivers of Bangladesh).
Acanthopagrus latus (not of Houttuyn); Bauchot & Smith 1983: SPARID Acanth 2 (Gulf of Mannar specimen only); Talwar & Jhingran 1991: 848 (Hooghly Estuary and Chilka Lake); Khan 2003: 9 (Sundarbans, India); Rahman 2005: 253 (tidal rivers of Bangladesh); Barman et al. 2007: 123 (Orissa, India); Rahman & Ruma 2007: 191 (tidal rivers of Bangladesh, incorrect image); Manisseri et al. 2012: 43 (Tuticorin, Gulf of Mannar); Joshi et al. 2016: 94 (Gulf of Mannar).
Acanthopagrus longispinnis; Iwatsuki & Carpenter 2006: 15 (in part, Bengal specimens only); Kume & Yoshino 2008: 51 (in part, Bengal specimens only); Iwatsuki & Heemstra 2010: 132 (in part, Bengal specimens only); Iwatsuki 2013: 76 (Ganges River and coastal area off Chennai); Mohanty et al. 2015: 11 (Chilka Lake: Orissa, list only); Pal et al. 2014:182 (Sundarbans, India; list only).
Sparidentex datnia; Iwatsuki & Carpenter 2006: 13 (in part); Kume & Yoshino 2008: 52 (in part); Iwatsuki & Heemstra 2010: 132 (in part); Iwatsuki 2013: 76, 85 (in part); Kottelat 2013: 353 (distribution unspecified, probably estuaries along upper Myanmar); Amir et al. 2014: 475; Pal et al. 2014: 182 (Sundarbans, India, list only).
Neotype (Neogenotype). BMNH 2018.9.11.1, 227 mm SL (X) (Fig. 5), Lower Ganges river basin at northern Sundarbans mangroves near Munshigonj, Satkhira, Bangladesh; stake net; spent female; purchased alive from Kolbari Bazar, Munshigonj, Satkhira by Mohammad Eusuf Hasan, 12 February 2016 (GenBank: COI—MK919178, 16S—MK919137, RAG-1— MK 919155).
Topotypes. Ganges estuary, south-western Bangladesh, Northern Bay of Bengal— AMS I.48389-006, 153 mm SL (X), Munshigonj, Satkhira; AMS I.48390-001, 185 mm SL (X), Chowrasta Fish Market, Kolapara, Patuakhali; BMNH 2018.9.11.2, 137 mm SL (X), Munshigonj, Satkhira; CUMS F507.19, 240 mm SL, Munshigonj, Satkhira; CUMS F507.21–25, 155– 320 mm SL, Munshigonj, Satkhira; CUMS F507.52, 150 mm SL, Mohipur Landing Centre, Kolapara, Patuakhali; CUMS F507.53, 262 mm SL, Chowrasta Fish Market, Kolapara, Patuakhali; CUMS F507.57, 154 mm SL, Munshigonj, Satkhira; CUMS F507.59, 145 mm SL, Munshigonj, Satkhira; CUMS F507.62, 133 mm SL, Munshigonj, Satkhira; CUMS F507.69–71, 157– 195 mm SL, Chowrasta Fish Market, Kolapara, Patuakhali; CUMS F507.94, 178 mm SL, Biponibag Fish Market, Chandpur, Meghna River; USNM 443797–98, 137– 230 mm SL, Munshigonj, Satkhira.
Other specimens. Northern Bay of Bengal, south-eastern Bangladesh —Lower Moheshkhali Channel, Cox’s Bazar AMS I.48388-003–004, 113–129 mm SL (X); AMS I.48391-001–002, 90.5–116 mm SL (X); BMNH 2018.9.11.5–8, 90– 150mm SL (male) (X); CUMS F507.08–09, 188–275 mm SL; CUMS F507.13–16, 84– 232 mm SL, Bakkhali Estuary; CUMS F507.30–37, 102– 203 mm SL; CUMS F507.39–41, 130– 137 mm SL; CUMS F507.43–48, 114– 129 mm SL; CUMS F507.65–67, 151– 167 mm SL; CUMS F507.78–79, 121– 128 mm SL; CUMS F507.82–85, 90– 97 mm SL; CUMS F507.88, 87 mm SL; CUMS F507.90–93, 68– 120 mm SL; MUFS 46106, 190 mm SL; USNM 443790–95, 85– 158 mm SL. Matamuhury Estuary, Chakaria, Cox’s Bazar: CUMS F507.02, 122 mm SL; MUFS 46105, 205 mm SL; MUFS 46107–10, 148– 220 mm SL. Naf Estuary at Teknaf, Cox’s Bazar (bordering: Myanmar): CUMS F507.03–07, 88–265 mm SL; CUMS F507.18, 255 mm SL; CUMS F507.72, 225 mm SL; USNM 443796, 195 mm SL.
Historic specimens identified as Acanthopagrus datnia. Ganges River Mouth, Bay of Bengal at Calcutta (= Kolkata), Bengal, British India: BMNH 1844.3.11.12, 220 mm SL (stuffed), Chrysophrys hasta, Günther (1859: 490) specimen (as “k”); BMNH 1844.3.11.13, 233 mm SL (stuffed), Chrysophrys hasta, Günther (1859: 490) specimen (as “e”); BMNH 1844.3.11.14, 225 mm SL (stuffed), Chrysophrys hasta, Günther (1859: 490) specimen (as “h”); BMNH 1857.6.13.106, 222 mm SL (stuffed), Chrysophrys hasta, Günther (1859: 490) specimen (as “i”, Dr. Cantor’s specimen, Pagrus flavopinnis, invalid name); BMNH 1857.6.13.107, 188 mm SL (stuffed), Chrysophrys hasta, Günther (1859: 490) specimen (as “c”, Dr. Cantor’s specimen, Pagrus flavipinnis, invalid name); BMNH 1858.8.15.3, 118.5 mm SL (spirit), Chrysophrys hasta, Günther (1859: 490) specimen (as “g”). Gulf of Mannar, South-western Bay of Bengal. India: CMFRI GB 31.142. 1, 240 mm SL, labeled as Acanthopagrus latus; Sri Lanka: BMNH 1991.7.12.40, 35.5 mm SL, labeled as Acanthopagrus latus.
Diagnosis. Distinguished from other species of Acanthopagrus by the following combination of characters: body moderately deep 2.0 ‒ 2.5 (mean 2.3) times in SL/BD (relatively slender in young and/or male specimens, and deeper in larger/gravid females); dorsal-fin rays XII, 10 (very rarely XI, 11 or XIII, 9; two each in 97 specimens); 3½ scale rows between fifth dorsal-fin spine base and lateral line; 4½ scale rows above lateral line, 10½ ‒ 11½ scale rows below lateral line; second anal-fin spine exceptionally robust: 17.5 ‒ 26.1% [mean 21%, n = 64] of SL in specimens <180 mm SL, and 13.6–19.8% [mean 17.2%, n = 27] of SL in specimens> 180 mm SL, much longer and stronger than third (2 AS /3 AS = 1.25–2.00, mean 1.6), it’s relative length decreases with increasing growth; pored lateral-line scales 42 ‒ 46 (mode 45); first soft dorsal-fin ray clearly longer than last dorsal-fin spine; pelvic and anal fins light yellow or yellow (Fig. 6A), caudal fin yellowish grey with a black margin (breadth about ¼ of caudal fin) (Fig. 5A, 6C); black streaks present proximally on inter-radial membranes between yellow anal-fin rays, even in preserved specimens (more prominent between second and fifth anal-fin rays); black blotches absent on inter-radial membranes between dorsal-fin rays; a black spot at the upper side of pectoral fin origin, persisting in preservatives; a weak diffuse dark blotch at origin of lateral line continuing over upper part of posterior opercle and upper cleithrum, becomes more prominent in (formalin) preservation.
Description. Counts and measurements of the neotype (BMNH 2018.9.11.1) and non-type specimens are given as percentages of SL in Table 2. The following description is for the neotype, followed by others in parentheses (if different). Characters stated in the diagnosis are not repeated.
Body fairly deep (juveniles relatively slender), compressed; upper profile notably convex and angular due to a bulge at eye; dorsal-fin spines appear alternately broad and narrow on either side; body scales feebly ctenoid, anteriorly similar to cycloid; mouth nearly horizontal and terminal; lips thick; snout strongly pointed, two nostrils just in front of eye; anterior nostril rounded and posterior one slit-like; maxilla reaching to below two thirds of posterior margin of pupil, longer than orbit diameter; lower jaw included slightly in upper jaw; teeth in both jaws in three to five rows, smaller anteriorly; typical molariform teeth strongly developed posteriorly (Fig. 7), six canines at front of both jaws; suborbital depth subequal to orbit; four or five transverse rows of scales on cheek; antero-dorsal profile ascending gently from just above eye, curved; anterior-most margin of head scalation broadly rounded, with small scales anteriorly, reaching to just posterior end or middle of the pupil; preopercular flange scale-less, posterior margin not serrated; scaly sheath at base of dorsal and anal fins; a long axillary pelvic process; dorsal-fin spines strong, fourth (and fifth) spine longest; first anal-fin spine clearly shorter than orbit diameter; second anal-fin spine flattened laterally, clearly longer than longest (fourth) dorsal-fin spine; third anal-fin spine shorter than the second anal-fin spine, longer than snout length; pectoral-fin tip nearly reaching to level with first anal-fin spine base, length greater than head length; first pelvic-fin ray length greater than (or subequal to) second anal-fin spine length; pelvicfin spine longer than snout length; three supraneural bones (0/0 + 0/2/); vertebrae 10 + 14.
Morphological changes with growth: Morphological examination of life history stages along with molecular data helps to resolve confusions on various species once described from younger specimens (Iwatsuki & Kimura 1997; Iwatsuki et al. 2001; Baldwin et al. 2009; Russell & Craig 2013, Russell et al. 2019). Fishes often show morphometric variation according to their sex, age and/or to the catching season (Günther 1859; Minos et al. 2008; Benchalel & Kara 2012; Sukumaran et al. 2016). The 2 AS in fishes usually grow relatively longer in immature and half-grown specimens (Günther 1859).
We observed some sort of variation in body shape and in the relative length of the second anal-fin spine. Fishes of similar length were found to belong to variable body depth (slender, SL:BD>2.4 vs deeper, SL:BD<2.4) (Fig. 8). However, close observations revealed no remarkable differences in morphometric data in these two forms, and no correlation was observed in between standard length and body depth. Macroscopic observation of gonads reveals that the slender forms were predominantly younger ones (usually <200 mm SL) and initial breeding males, while the larger ones (usually> 200 mm SL) were predominantly breeding females. This probably reflects protandrous hermaphroditism in Acanthopagrus datnia. As usual, the gravid females were observed to be deeper bodied while the spent ones are relatively slender in shape.
Analysis of 2 AS measurements of Acanthopagrus datnia showed growth related changes in the proportions of standard length. The relative length of 2 AS was found to decrease with increasing growth (r = -0.80, p = <0.0001), i.e., the younger fishes have relatively longer sized second anal-fin spines which become proportionally shorter with growth (Fig. 9). Initial breeding males also tend to be more slender in shape than breeding females.
Colour when fresh: Based on a colour photographs of the Neotype, BMNH 2018.9.11.1 (Fig. 5A) and others (Fig. 6, 8): Head and body silvery pale grey; belly whitish-silvery with streaks along longitudinal scale rows; dorsal fin grayish to hyaline or blackish-gray; pelvic and anal fins yellowish and whitish; caudal fin yellowish grey with dark blackish margin; pectoral fins somewhat yellowish hyaline, a black spot/blotch at upper side of the origin or axil of pectoral fin; black streaks proximally on inter-radial membranes between yellow anal-fin rays, more prominent between second and fifth anal-fin rays; a weak diffuse dark blotch at origin of lateral line continuing over upper part of posterior opercle and upper cleithrum.
Colour in preservative: Head, body and all fins yellowish-tan; a dark defused blotch at origin of lateral line, a black spot at upper side of the axil of pectoral fin, and black streaks proximally on inter-radial membranes between yellow anal-fin rays are persistent in preservation (Fig. 5B).
Size: Attains ca. 50 cm total length, weighing around 2 kgs.
Distribution. Acanthopagrus datnia is currently known from mangrove fringed, estuarine and coastal areas of the entire northern, eastern and western coast of the Bay of Bengal (Fig. 2): centrally—in lower basins of the Ganges River (type locality: Sundarbans mangroves and adjacent areas in Bangladesh, and in West Bengal, India); in the western Bay of Bengal—in Lake Chilka (Orissa, India), Parangipettai Coast and shallow coastal area off Chennai (Tamil Nadu, India), Gulf of Mannar (Tamil Nadu, India), and Negumbu Estuary (Sri Lanka); in the eastern Bay of Bengal—in all the estuaries of eastern Bangladesh (the Sangu, Matamuhuri, Sonadia, Bakkhali and Naf), upper Myanmar (the Kaladan Estuary), and probably also in the Irrawady Delta and Gulf of Martaban. Nevertheless, it is endemic to the Bay of Bengal region.
Etymology. Hamilton (1822) used common vernacular names in latinised form in naming most of his nominal species. Coius datnia was no exception to this, where the species name was derived from its local name Daitna Mas or Datina Mas known in lower Ganges estuarine areas, across all of coastal Bangladesh and in West Bengal of India. We follow the common English name, “Bengal Yellowfin Seabream” suggested by Iwatsuki (2013).
Habitat, biology and life history. Acanthopagrus datnia is known to occur in all the mouths of the Ganges (Hamilton 1822), especially in the mangrove fringed canals in the northern Bay of Bengal region. Acanthopagrus datnia probably has a single short duration spawning season in southern Bangladesh—in winter, predominantly in December–January, indicating an apparently inverse relationship of spawning with water temperature (Hasan 2009). The sequence of sexual phases in relation to sizes indicates A. datnia to be a protandrous hermaphrodite (initial males changing to female). Some individuals, however, remain female from early life, i.e., not changing sex at all (Hasan 2009), though they may not be fully functional at that time. Recruitment of juveniles (~ 20 mm SL) in estuaries of south-eastern Bangladesh commences on mid-winter (early January) with a peak during spring and early summer (March-April) (Hasan 2009).
Acanthopagrus datnia is a commercially important fish in its range, though not very common in markets. It is usually harvested by fixed shore encircling stake nets, set at intertidal mangrove-fringed muddy shores, and by hand-lines (predominantly larger individuals). Further study is required to have a detailed picture of reproductive biology and population parameters.
Intraspecific genetic similarity. The ML analyses based on couple of mitochondrial CO1 (Fig. 3), and 16S (Fig. 4A) and nuclear RAG-1 (Fig. 4B) resulted no clustering in respect of having 2 AS above or below 21% of SL and/or body shape slender or deeper. The intra-species divergence (Kimura-2 parameter) estimated using CO1and RAG sequences were 0.2% and 0.1%, respectively. No nucleotidic polymorphism was recovered in the A. datnia samples using 16S sequences. All these analyses confirm the genetic integrity of A. datnia in Northern Bay of Bengal, the type locality (Fig. 2). The two gross body types (Fig. 8), and different length of the second anal-fin spine, are therefore considered simply as intraspecific variations of a single species, which may be due to variation of body shape of male and female specimens during the breeding season (Benchalel & Kara 2012), or variation with growth and adaptation, and condition factor (Sukumaran et al. 2016).
Remarks. Coius datnia Hamilton 1822 was considered as belonging to genus Acanthopagrus (Günther 1859; Day 1875 - 78; Bleeker 1877; Fowler 1929 & 1933; Munro 1949; Rahman 1989 & 2005; Talwar & Jhingran 1991; and Kottelat 2000, see Discussion of synonymies below). However, several authors recently suggested the species be placed in the genus Sparidentex stating the reason that the original description does not mention the presence of molars (Iwatsuki & Carpenter 2006; Kume & Yoshino 2008; Iwatsuki & Heemstra 2010; Iwatsuki 2013; Amir et al. 2014). No type of Coius datnia was designated, but the species was drawn as a fine figure (Hamilton 1822: 88, 369, pl. 9, fig. 29; Fig. 1A). Such figure apparently looked similar to Sparidentex hasta in overall appearance and colouration of body (Fig. 14A, B) and generated confusion in determining the taxonomic identity of Coius datnia. However, it is significant that although Hamilton (1822) did not use the term ‘molars’, he described the inner teeth of C. datnia as ‘blunt and crowded together’: “ The anterior teeth in both jaws are sharp, conical, of unequal size, and placed in a single row: the posterior ones are blunt and crowded together ” (Hamilton 1822, p. 88). Such a description explicitly suggests the presence of molars (McGrouther 2015), which supports the current generic allocation of Coius datnia Hamilton, 1822 to Acanthopagrus, rather than Sparidentex. Besides, the genus Sparidentex usually has 11 dorsal-fin spines and 11 dorsal soft-rays and a much slender body (Amir et al. 2014; Siddiqui et al. 2014; Iwatsuki & Heemstra in press; Iwatsuki & Carpenter, in prep.), while the figure of Coius datnia has 12 dorsalfin spines and 10 dorsal soft-rays (Fig. 1A). Accordingly, we concluded that Coius datnia belongs to a species of the genus Acanthopagrus. Furthermore, we assume that Sparidentex species are not distributed in the northern Bay of Bengal. Despite intensive sampling for last 15 years, the authors did not find any Sparidentex species there but only Acanthopagrus berda and A. datnia.
There was noticeable variation in body shape and in the relative length of the second anal-fin spine. The larg- er second anal-fin spine in the lectotype and in one paralectotype (designated by Iwatsuki 2013, formerly two syntypes), of Acanthopagrus longispinnis (Valenciennes, 1830), MNHN 5282 (Fig. 10), are in fact, smaller-sized specimens of A. datnia. They strongly conform to the above descriptions and morphometrics of Coius datnia. Acanthopagrus datnia is thus justified as a senior synonym of A. longispinnis.
Neotype designation: Coius datnia Hamilton, 1822 was described on the basis of specimens from the mouths of the Ganges, in then Bengal, British India. Like all of his nominal species, Hamilton (1822) did not designate any type specimens for this species. This resulted considerable confusion in determining the correct taxonomic identity of this species (See Discussion below). In order to avoid further confusion, a neotype of C. datnia is designated for a specimen (BMNH 2018.9.11.1, 227 mm SL) collected from the type locality (lower Ganges river mouths at Sundarbans Mangrove Canals near Munshigonj, Satkhira, Bangladesh). The neotype designation for Coius datnia is justified (Kottelat 2000) as applicable according to ICZN (2013) (Art. 75.3.1–75.3.7).
description: Published as part of Hasan, Mohammad Eusuf, Durand, Jean-Dominique & Iwatsuki, Yukio, 2020, Acanthopagrus datnia (Hamilton, 1822), a senior synonym of Acanthopagrus longispinnis (Valenciennes, 1830) (Perciformes: Sparidae), pp. 151-181 in Zootaxa 4750 (2) on pages 159-167, DOI: 10.11646/zootaxa.4750.2.1, http://zenodo.org/record/3707261