Sardinella albella ( Valenciennes, 1847 )

Hata, Harutaka & Koeda, Keita, 2022, First Japanese Records of Sardinella albella (Teleostei: Clupeiformes: Clupeidae) from Okinawa Island, with a Key to Japanese Species of Sardinella, Species Diversity 27 (1), pp. 37-43 : 37-40

Sardinella albella ( Valenciennes, 1847)

[English name: White Sardinella ; new standard Japanese name: Ginrin-sappa] ( Figs 1 , 2 ; Tables 1, 2)

Material examined. Three specimens, 69.3–75.6 mm SL: ZUMT 17185, 71.9 mm SL ( Fig. 1A ), ZUMT 17186, 75.6 mm SL ( Fig. 1B ), ZUMT 17187, 69.3 mm SL ( Fig. 1C ), Baten Port, Nakagusuku Bay, Nanjo City, Okinawa Island, Ryukyu Archipelago, Japan (26°10′N, 127°46′E); coll. by Sadao Tanabe, donated to Shigeho Tanaka; collection date unknown, but estimated as 1920 to 1930 (see “Comparisons between S. albella and previous records of unidentified species of Sardinella from Japan ”).

Description. Body oblong, strongly compressed. Body deepest at dorsal-fin origin. Dorsal contour rising from snout tip to dorsal-fin origin, thereafter gently lowering to uppermost point of caudal-fin base. Ventral contour lowering from lower-jaw tip to just below pectoral fin, thereafter gradually elevated to lowermost point of caudal-fin base. Abdomen covered with 31 prominently keeled scutes from isthmus to anus. Mouth terminal, small, posterior tip of maxilla slightly short of anterior margin of pupil. Ventral margin of maxilla with small uniserial teeth. Premaxilla and hypomaxilla without teeth. First supramaxilla elongated longitudinally. Second supramaxilla paddle-shaped, vertically symmetrical. Posterior ramus of lower jaw elevated. Orbit elliptical, horizontal axis longest. Eye large, positioned laterally on head dorsal to horizontal through pectoral-fin insertion, visible in dorsal view. Eye round, covered with adipose eyelid. Anterior part of eye exposed. Pupil round. Interorbital space flat. Nostrils close to each other, anterior to orbit, dorsal-ventral dimension slightly elongate. Posterior margins of preopercle, subopercle and opercle convex, rounded, without serrations. Pseudobranchial filaments present on inner surface of opercle, exposed. Two fleshy outgrowths on posterior margin of gill opening; a single large papilla on ventral margin. Gill rakers long, slender, with numerous asperities on anterior and posterior faces. Gill filaments longer than corresponding gill rakers. Pectoral-fin insertion slightly anterior to posterior margin of opercle. Posterior tip of pectoral fin pointed, just short of reaching vertical through dorsal-fin origin. Dorsal, ventral, and posterior margins of pectoral fin nearly straight. Dorsal most ray of pectoral fin unbranched, all others branched. Anterior margin of dorsal fin elevated from fin origin to fourth ray tip; middle portion of dorsal-fin margin slightly concave. Dorsal-fin first ray minute, located closely to second ray; anterior four rays unbranched, others branched; posteriormost ray not filamentous. Pelvic-fin insertion just below base of ninth or tenth dorsal-fin ray. Posterior tip of depressed pelvic fin pointed, not reaching anus. Anterior and posterior margins of pelvic fin nearly straight. Anteriormost ray of pelvic fin unbranched, others branched. Anal-fin origin just behind anus. Last two anal-fin rays enlarged. Anus oval, horizontal axis longest. Caudal fin forked, upper and lower margins straight. Tips of both jaws point- ed, lower-jaw tip slightly projecting beyond snout tip. Scales cycloid, thin, deciduous, those on lateral body surface with several centrally discontinuous vertical striae, without perforations ( Fig. 2 ). Predorsal scales paired. No elongate winglike scales present beneath normal paired scales. No scales on head and most fins; a broad triangular sheath of scales on caudal fin.

Color of preserved specimens: Dorsum to upper part of lateral surface of body dark purplish-brown. Lower part of lateral surface and ventral surface of body uniformly pale brown. Pectoral, pelvic, and anal fins semitransparent, pale, without melanophores except for uppermost pectoral-fin ray. Dorsal and caudal fins uniformly pale, melanophores scattered along fin rays. Dark blotch on dorsal-fin origin ( Fig. 1B ).

Distribution. Sardinella albella is widely distributed in Indo-West Pacific tropical waters, from the east coast of Africa to northern Australia and the Ryukyu Archipelago including the Red Sea and the Persian Gulf ( Whitehead 1985; Munroe et al. 1999; Matsuura et al. 2001; Yoshino 2009, 2015, 2018; Matsunuma 2011, 2013; Stern et al. 2015, 2016; Hata 2019; this study). In Japan, the species is known only from Nakagusuku Bay, east coast of southeastern Okinawa Island, Ryukyu Archipelago (this study).

Identification. The specimens collected from Okinawa Island were assignable to the genus Sardinella as defined by Whitehead (1985) and Munroe et al. (1999), having prominently keeled scutes on the abdomen, paired predorsal scales, a symmetrical second supramaxilla, toothless hypo-maxilla, anal fin with two posteriormost fin rays enlarged, and the gill opening with two fleshy outgrowths on the posterior margin. They further conformed to Sardinella albella , having the following combination of characters that closely matched the diagnostic features given by Whitehead (1985), Munroe et al. (1999), and Stern et al. (2016): caudal fin uniformly pale, lacking a distinct blotch; black spot on dorsal-fin origin; striae on scales on lateral body surface interrupted centrally; 30−32+56−59=86−90 gill rakers on first gill arch; and 18+13=31 keeled scutes along body ventral surface.

In particular, meristic and morphometric characters of the Okinawa specimens generally matched those given by Stern et al. (2016) for Sardinella albella , although they differed slightly from Stern et al. (2016) ’s specimens in having slightly lower total ray counts for the dorsal, anal, and pectoral fins, and higher counts of upper gill rakers on the first gill arch and pseudobranchial filaments ( Table 1). However, specimens of S. albella examined by Stern et al. (2016) were collected only from the Indian Ocean (Red Sea, eastern coast of Africa, and India), and the above minor differences were judged as intraspecific or regional variations only.

Comparisons between S. albella and previous records of unidentified species of Sardinella from Japan. As stated in Hata and Motomura (2021b), several unidentified/indeterminate species of Sardinella have been reported from Japan. Clupea immaculata Kishinouye, 1908 , of uncertain taxonomic status (possibly a junior synonym of S. aurita or S. gibbosa ) according to Hata and Motomura (2021b), clearly differs from S. albella by having 19+14 scutes covering the abdomen (vs. 18+12 or 13=30 or 31 in S. albella ; Kishinouye 1908; Stern et al. 2016; this study). Clupea exile Kishinouye, 1911 , also of uncertain taxonomic status ( Yoshigou 2002; Aonuma and Yagishita 2013; Hata and Motomura 2021b), has distinctively lower vertebral counts than in the specimens of S. albella examined here (40 vs. 44–46; Kishinouye 1911; this study; Table 1).

Aoyagi (1941) reported Sardinella sindensis (Day, 1878) from Miyako Island, Japan, based on three specimens (54.7–60.2 mm SL). Subsequently, Matsubara (1955) listed the following diagnostic characters for S. sindensis sensu Aoyagi (1941) : pelvic fin with eight fin rays, black spot on dorsal-fin origin, lower gill rakers on first gill arch 58–62, body depth 3 to 4 times (approx. 25.0–33.3%) in SL, and eye diameter 3.5 to 4 times (approx. 25–28.6%) in head length. However, the distributional range of S. sindensis is limited to the northwestern Indian Ocean, from the Gulf of Aden to the western coast of India ( Whitehead 1985). Although the gill raker counts of Aoyagi (1941) ’s S. sindensis are included within the range of those shown for S. albella by Stern et al. (2016) and the present study (47–64), Aoyagi’s specimens were smaller than in the latter studies (54.7–60.2mm SL vs. 63.9–130.0 mm in Stern et al. 2016; 69.3–75.6 mm in this study), a significant consideration given that the gill raker counts of some clupeoid fishes (including S. albella ) are known to increase with increasing body length ( Whitehead 1985; Munroe et al. 1999). In fact, S. sindensis sensu Aoyagi (1941) is most likely to be Sardinella alcyone Hata and Motomura, 2019 (lower gill rakers on first gill arch 64–72 in 66.6–109.8mm SL specimens; Hata and Motomura 2019c). Therefore, the specimens described herein represent the first certain records of S. albella from Japanese waters, with Nakagusuku Bay, Okinawa Island being confirmed as the northern distribution limit of the species in the Pacific Ocean.

Because a Japanese name has not been proposed previously for S. albella , the new standard Japanese name “Ginrin-sappa” is herein proposed for the species (based on ZUMT 17186; Fig. 1A ), “ginrin” meaning “silver scales”, in reference to the shiny silver scales on fresh specimens (Hata 2019), and “sappa” being the Japanese name for the genus Sardinella . Including S. albella , seven species of Sardinella have been confirmed in Japanese waters (see Key below; Aonuma and Yagishita 2013; Hata and Motomura 2019a, c, 2021b; this study).

Sardinella albella is abundantly caught in Taiwan and Philippines ( Willette et al. 2011; Hata 2019). The occurrence of the species in Okinawa Island is thought to be a result of the transportation from the southern areas such as Taiwan and Philippines by Kuroshio Current. Because the “10,000” series of ZUMT specimens were collected from 1920 to 1930, the present specimens were collected at least 90 years ago. During an ongoing taxonomic review of Sardinella from Japanese waters by the first author, no specimens of S. albella collected after the 1930’s have been located. In Nakagusuku Bay, the collection locality of the specimens examined herein, fishery catches of two other clupeoid species, Nematalosa come (Richardson, 1846) and Nematalosa japonica Regan, 1917 , have significantly decreased following progressive infilling of the bay since the 1980’s ( Uehara et al. 2015). As in the case of the two latter species, the environment that individuals of S. albella transported by Kuroshio Current can inhabit may have decreased due to changes in the coastal environment of Nakagusuku Bay. To better understand the distribution patterns of S. albella in the northwestern Pacific, fisheries surveys of the Nakagusuku Bay and other potentially suitable habitats of S. albella in Okinawa are necessary including comparative genetic analyses from collected material.

Figures

Fig. 1. Formalin-preserved preserved specimens of Sardinella albella from Nakagusuku Bay, Okinawa Island, Ryukyu Archipelago, Japan [A: ZUMT 17185, 71.9mm SL; B: ZUMT 17186, 75.6mm SL; C: ZUMT 17187, 69.3mm SL (a: lateral, b: dorsal, c: ventral views)].

Fig. 2. Stained scale removed from left side of midbody (just above pectoral fin) of Sardinella albella from Nakagusuku Bay, Okinawa Island, Ryukyu Archipelago, Japan (ZUMT 17185, 71.9mm SL).