Gnathanodon Bleeker 1850

Genus Gnathanodon Bleeker 1850 View in CoL

Gnathanodon speciosus (Forsskål 1775)

Common name: Golden trevally ( Figures 1 View Figure 1 , 2 View Figure 2 )

1775. Scomber speciosus Forsskål (in Niebuhr), Descr. Anim., p. 54, pl. xii (type locality: Jeddah , Saudi Arabia, Red Sea) .

2003. Gnathanodon speciosus Allen and Adrim, Zool. Stud. , 42 (1): 38 ( Indonesia).

Materials examined: ZSI F 12909/2, 2 ex., 118.7 - 133.4 mm SL, 22°09’07.0”N, 88°53’55.0”E, off Garal River , Satjelia Island , Gosaba , Sundarbans , Dakshin 24 Parganas, West Bengal, India, bag net fishing, 24-iv-2018, coll. P. Chakraborty. GoogleMaps

Meristic characters: Dorsal-fin rays VII - I/19 - 21; pectoral-fin rays 22; pelvic-fin rays I/5; anal-fin rays II - I/16 - 17; scutes 21 - 22; curved lateral line scales 62 - 69; gill rakers on lower limb of first-gill arch 19 - 20.

Description: Body deep, compressed; dorsal profile moderately convex anteriorly; poorly developed adipose eyelids; lips papillose; upper jaw strongly protractible, maxilla reaching to below front edge of eye; minute teeth on lower jaw; breast wholly scaly; caudal peduncle moderately compressed; caudal fin deeply forked.

Proportions as % of SL: body depth 45.8 - 48.8; head length

32.6 - 36.4; curved lateral line length 35.3 - 40.2; straight lateral line length 41.0 - 45.5. Soft dorsal-fin base length

52.2 - 55.1; soft anal-fin base length 37.5 - 41.3; soft dorsal-fin lobe height 18.6 - 23.2; soft anal-fin lobe height 16.8 -

20.1; pectoral-fin length 28.7 - 30.0; snout to origin of spinous dorsal-fin 37.9 - 40.8; maximum scute length 1.8 -

2.1. Proportions as % of head length: eye diameter 19.2 -

24.4; snout length 33.2 - 34.2; postorbital length 45.8 - 47.6; upper-jaw length 41.9 - 43.1.

Colouration: When fresh, body bright yellow with 10–11 alternating broad and narrow dark bands across sides. All fins yellow, caudal-fin lobes black. After fixation, body silvery above and below, breast area with golden tinge. Pectoral fins partially yellow, pelvic fins white. Dorsal, anal, and caudal fins dusky, 10–11 alternating broad and narrow dark stripes along sides.

Distribution: Gnathanodon speciosus is widely distributed from the Indo-Pacific to the eastern Pacific, occurring from the Persian/Arabian Gulf to southern Japan and Australia, and further to Tonga, Hawaii, the Austral Islands, and along the coast from Mexico to Ecuador ( Smith-Vaniz, 2022). In India, it occurs along the entire coastline, from Gujarat to West Bengal, and extends to the Andaman and Nicobar Islands ( Ranjan, 2017). The specimens for this study were collected from the mangrove-associated waters of the Sundarbans in West Bengal.

Remarks: The genus Gnathanodon Bleeker 1850 , is monotypic. It is distinguished from other genera within the Carangidae family by weak teeth present only in the lower jaw of juveniles and absent absent in adults, poorly developed adipose eyelids, and fleshy lips ( Smith-Vaniz, 1999). The collected specimens can be distinguished from other carangid species in the Sundarbans by the following features: two dorsal fins; a deep, compressed body; a somewhat rounded head; non-filamentous dorsal- and anal-fin rays; poorly developed adipose eyelids; and 10 - 11 alternating black bands along the sides ( Figure 2 View Figure 2 ).

Talwar et al. (1992) first reported G. speciosus from coastal West Bengal, a finding later confirmed by Ray et al. (2021). Beyond these coastal records, this study documents the first occurrence of G. speciosus in the mangrove-associated waters of the Indian Sundarbans, contributing to the ichthyofaunal diversity of the region. The species has also been reported from other mangrove-associated habitats in Odisha, Maharashtra, Goa, and the Andaman & Nicobar Islands ( Mishra et al., 2019). We hypothesise that wind, wave action, and possibly rising water temperatures may explain its inland range expansion within the Sundarbans, potentially moving in from coastal West Bengal. With this record, the total number of carangid species reported from the Sundarbans rises to 13.