Sillago soringa Dutt & Sujatha, 1982

Figures 4 & 5, Table 2

Sillago soringa Dutt & Sujatha, 1982: 611–614, fig. 1 (India, Visakhapatnam).

Soringa sillago

Materials examined. Bangladesh: FL_JNU uncat. [SS22015, SS22035, SS22042, SS22043 and SS22044], 5 specimens, 81.8–101.2 mm SL, St. Martin’s Island, 20.62°N, 92.32°E, February 2020; additional 25 specimens, 69.6–102.2 mm SL, St. Martin’s Island, February 2020. India: 4 specimens, 116.6–123.9 mm SL, Chennai, 13.29°N, 80.32°E, December 2019; F7734/2, holotype; F7735/2, 4 paratypes, 123.0–153.0 mm TL, Visakhapatnam, photograph.

Comparative material: Sillago vincenti: FL_JNU uncat. [CH12191 – CH121910], 10 specimens, 141.8–220.3 mm SL, December 2019, India, Chennai. Sillaginopsis domina: FEL_OUC uncat. [tissue sample 142276, 142284, and 142293], 3 specimens, Bangladesh, Cox’s Bazar, October 2018; FL_JNU uncat. [PP121910, PP121915 and PP121916], 3 specimens, 180–195 mm SL, December 2019, Bangladesh, Patharghata.

Diagnosis: Sillago soringa is differentiated by dorsal-fin rays X–XI + I,20–22; anal-fin rays II,20–22; 68–72 lateral line scales; 4–5 scales above the lateral line; 4 + 8–9=12–13 gill rakers on the first arch; 12–14 (mostly 13) abdominal, 6–7 (mostly 7) modified, 11–14 (mostly 13) caudal, and 32–34 (mostly 33) total vertebrae; swimbladder long with a single anterior extension and a single posterior extension, short anterolateral extension and ten lateral processes. The general body shape is shown in Figure 4A. Counts and measurements are given in Table 2.

Color of fresh specimens (Fig. 4A): Body brown dorsally, whitish ventrally. Dorsal fins hyaline dusted with black dots, with dots on second dorsal fin arranged in two longitudinal rows.Anal fin light yellowish to whitish dusted with black dots. Caudal fin mainly hyaline, with dusky pigment posteriorly. Pectoral and pelvic fins hyaline.

Swimbladder (Fig. 4B & C): The swimbladder with one anterior extension projecting forward, anterolateral extension curved backward along each side for a short distance, only one posterior extension, and ten lateral processes. The duct-like process is visible.

Distribution: Sillago soringa is distributed in the northern Indian Ocean, including the southeast coast of India (Jayasankar 1991), the east coast of India (McKay 1992) and presently, the southernmost part of Bangladesh (St. Martin’s Island) (Fig. 5).

Comparison: Meristics, morphometric measurements and structure of the swimbladder of S. soringa from Bangladesh match the previous description of S. soringa from India by Dutt & Sujatha (1982) (Table 2). Frequency distribution for meristic counts is given in Table 3.

Often Sillago mengjialensis Gao, Baki & Saha, 2022, S. muktijoddhai, and S. soringa were found as a mixed group, so identification should be made based on body color and swimbladder morphology. As S. soringa resembles S. sihama but is difficult to differentiate without observation of the swimbladder (Dutt & Sujatha 1982; McKay 1992), it was most probably misidentified as S. sihama in Bangladesh. The species can be distinguished from S. sihama by having 33 vertebrae (versus 35), black dots on the anal fin and its swimbladder structure (a single posterior extension in S. soringa versus two posterior extensions in S. sihama). Sillaginopsis domina (Cuvier, 1816) can be differentiated easily from S. soringa by a very elongated second dorsal-fin spine, small eyes and absence of a swimbladder.

Sillago soringa is also similar to and can be confused with S. vincenti McKay, 1980, S. boutani Pellegrin, 1905 and S. asiatica McKay, 1982 but these three species have not yet been recorded from Bangladesh. However, S. soringa can be distinguished from these three species by combination of several characters, e.g., absence of black dots on body below lateral line, presence of black dots on the anal fin, number of vertebrae (usually 33 versus 34–38 in other three species) and swimbladder structure (Table 4). Among these four species, S. soringa is more similar to S. asiatica, but the anterolateral extension of the swimbladder is much shorter in S. soringa than in S. asiatica. Differences in the structure of the swimbladder among S. soringa, S. asiatica, S. vincenti and S. boutani are shown in Figure 4C–F.