Sillago sihama (Fabricius, 1775)

Saha, Shilpi, Bogorodsky, Sergey V., Baki, Mohammad Abdul, Gao, Tianxiang, Mckay, Roland J., Alpermann, Tilman J. & Song, Na, 2024, Assessment of the diversity of the family Sillaginidae in the Indian Ocean with emphasis on the taxonomic identity of Sillago sihama, Zootaxa 5493 (5), pp. 451-485 : 463-467

Sillago sihama (Fabricius, 1775)

Figures 1A–C , 2A & B , 3 , 8B , Table 2

Atherina sihama Fabricius in Niebuhr (ex Forsskål), 1775: 70 (Red Sea, Yemen, Al-Luhayya).

Northern whiting; Sand smelt; Silver sillago

Materials examined. Bangladesh: FEL_OUC uncat. [tissue sample M8191–M8193], 3 specimens, 88.7–140.8 mm standard length (SL), Maheshkhali, 21.77°N, 91.89°E, August 2019 ; FL_ JNU uncat. [MA12038–MA12051], 14 specimens, 77.0– 100.2 mm SL, Maheshkhali, January 2020 ; FL_ JNU uncat. [ SM112101 – SM112107 ], 7 specimens, 112.4–159.0 mm SL, St. Martin’s Island , 20.61°N, 92.32°E, November 2021 ; additional 40 specimens, 76.6–110.3 mm SL, Maheshkhali, January 2020; 7 specimens, 63.3–143.5 mm SL, Cox’s Bazar (21.45°N, 91.96°E), November 2019 . southern Red Sea : HUJF 19716 , 184.0 mm SL, Eritrea, photograph ; KAUMM 462 [ KAU12-006 ], 182.0 mm SL, Saudi Arabia, off Jizan, 15 February 2012 ; KAUMM 67 [ KAU12-789 ], 124.0 mm SL, Saudi Arabia, off Jizan, 29 February 2012 ; KAUMM 67 [ KAU12-789 ], 112.0 mm SL, Saudi Arabia, off Jizan, 01 March 2012 ; SMF 35900 [ KAU14-301 ], 195.0 mm SL, Saudi Arabia, off Jizan, 01 November 2014 ; SMF 35911 [ KAU14-351 ], 135.0 mm SL, Saudi Arabia, off Jizan, 04 November 2014 .

Comparative material: Sillago erythraea : SMF 35017 [ KAU 12-790 & 791], 2, 128.0–134.0 mm SL, southern Red Sea, Saudi Arabia, off Jizan, 29 February 2012; KAUMM 468, 120 mm SL, southern Red Sea, Saudi Arabia, off Jizan, 31 October 2014. Sillago mengjialensis : FEL_OUC142378, holotype, 98 mm SL, Bangladesh, Cox’s Bazar. Sillago muktijoddhai : FEL_OUC142377, holotype, 92 mm SL, Bangladesh, Cox’s Bazar. Sillago cf. sihama 2: ZJOU _ FEBL 021131, 131.0 mm SL, China, Fujian, Zhangzhou, photograph.

Diagnosis: Sillago sihama is distinguished by dorsal-fin rays XI + I,20–23; anal-fin rays II,21–23; 66–74 scales in the lateral line; 4–5 scales above the lateral line; 3–4 + 8–9 gill rakers on the first arch; 12–15 (mostly 14) abdominal, 5–10 (mostly 8) modified, 11–16 (mostly 13) caudal and 32–35 (mostly 35) total vertebrae. The body is brownish dorsally, silver ventrally; area between posterior nostril and dorsoanterior edge of orbit unpigmented; first dorsal fin with black pigment on first two membranes at spine tips; anal fin lacking black dots. The swimbladder is long with two anterior extensions, two posterior extensions without a lacuna at the base; the anterolateral extension of the swimbladder extends into the anterior short blind tubule and posterior one kinked, long and complex, and 10–11 lateral processes. The general body shape is shown in Figure 1A–C . Counts and measurements are given in Table 2. Frequency distribution for meristic counts is given in Table 3.

Color of fresh specimens ( Fig. 1A & B ): The body is unmarked, brownish, silvery gray or silvery tan dorsally, silver on sides and ventrally. Area between posterior nostril and dorsoanterior edge of orbit unpigmented. First dorsal fin with some dusky pigment on the membranes, first two membranes much darker at spine tips; membranes of the second dorsal fin with dusky pigment adjacent anteriorly to each ray. The anal fin is light yellowish to whitish without black dots, with a white margin along anterior one-third of the fin. The caudal fin is light yellowish, usually blackish along dorsal and ventral edges of each lobe. Pectoral and pelvic fins are light yellowish.

Swimbladder ( Fig. 2A & B ): The swimbladder is long. Two anterior extensions are divided and end on each side of the basioccipital over the auditory capsule. An anterolateral extension originates anteriorly on both sides of the swimbladder and then bifurcates into anterior and posterior subextensions. The anterior subextensions are short, simple blind tubules, but the posterior one is kinky, long and complex, extending along the abdominal wall and terminating near the bases of two posterior extensions. The entire lateral surface of the main body of the swimbladder has 10–11 robust and horn-like lateral processes (anterior 4–5 stout and horn-like, posterior 6–7 small and triangular) and penetrate the musculature. Posterior sub-extensions of the swimbladder are ventrally adjacent to the lateral processes but not interconnected with each other. Two posterior tapering extensions of the swimbladder extend into the caudal region. Bases of the two posterior extensions are adherent and two posterior extensions are well-knit, without a lacuna in between. A single duct-like process arises from the ventral surface of the swimbladder, and extends to the urogenital opening. The duct-like process originates anteriorly at the termination of the swimbladder and anterior to the base of two posterior extensions. A sub-extension is attached to the sanguineous vesicle near the vertebrae.

Distribution: Sillago sihama , originally described from the southern Red Sea ( Yemen), is widely distributed in the Indian Ocean, sampled from the southern Red Sea ( Eritrea and Saudi Arabia), Arabian Sea (western India, Pakistan), northeastern Arabian Gulf (Hormozgan, Iran), South Africa (Mlalazi Estuary, Tugela Bank and Mhlathuze Estuary), and Bay of Bengal, Bangladesh (Maheshkhali, Cox’s Bazar and St. Martin’s Island) ( Lakra et al. 2011; Golani et al. 2013; Bogorodsky et al. 2014; Steinke et al. 2016; Cheng et al. 2020; Divya et al. 2021 (as S. intermedius ); Amir et al. 2022; Afrand et al. 2023; present study) ( Fig. 3 ).

Remarks: Habib & Islam (2020) listed S. sihama from Bangladesh based on six sources, but all these publications lack descriptions of collected material. Later, Ahmed et al. (2021) included specimens under the name S. sihama in their phylogenetic analysis, but further study revealed that this material represents another species, namely Sillago muktijoddhai Gao & Saha, 2022 . Accordingly, S. sihama is reported as the first confirmed, easternmost record from Bangladesh in the present study.

Unfortunately, there is no published literature on the structure of the swimbladder for S. sihama samples from India, Pakistan, Iran and South Africa. However, there were marked differences in the swimbladder between specimens from Bangladesh ( Fig. 2A & B ) and Eritrea based on available published literature ( Golani et al. 2013; Fig. 2C in present study). According to Golani et al. (2013), the swimbladder of Sillago sihama ( Eritrea) lacks an anterior subextension of the anterolateral extension, and the two posterior tapering extensions are separated from each other. The posterior sub-extensions of the anterolateral extension are smooth but differ from those in S. sihama ( Bangladesh). These differences include the presence of an anterior subextension of the anterolateral extension, two posterior extensions joined to each other, and each posterior subextension of the anterolateral extension is a complex. Previously Kaga (2013) raised this question with detailed comments and stated that Golani et al. (2013) must have overlooked anterior sub-extensions of the anterolateral extension. Moreover, these authors did not provide any swimbladder photographs (just schematic drawings) and did not indicate which specimens were examined for swimbladder morphology. Therefore, swimbladder morphology described in the present study is applicable to the true S. sihama and can be useful for comparison with undescribed species in future.

Figures

FIGURE 1. A: Sillago sihama, KAUMM 462 [KAU12-006], 182.0 mm SL, Jizan, SaudiArabia, southern Red Sea; B: S. sihama, SMF 35900 [KAU14-301], 195.0 mm SL, Jizan, Saudi Arabia, southern Red Sea; C: S. sihama, 98.9 mm SL, Maheshkhali, Bangladesh; D: S. cf. sihama 2, ZJOU_FEBL021131, 131.0 mm SL, Fujian, Zhangzhou, China (Xiao 2018).

FIGURE 2. A & B: Swimbladder of Sillago sihama, Bangladesh; C: Swimbladder of Sillago sihama, Eritrea, southern Red Sea (Golani et al. 2013); D: Swimbladder of Sillago cf. sihama 2, China (Xiao 2018).

FIGURE 3. Distribution of Sillago sihama in the Indian Ocean.

FIGURE 8. Head close-up showing area between posterior nostril and dorsoanterior edge of orbit. A: Sillago erythraea. SMF 35017; B: Sillago sihama, KAUMM 67. Photos by Sven Traenkner (SMF).