Spratelloides atrofasciatus Schultz, 1943

Hidaka, Kouichi, Yamamuro, Taihei & Yoshino, Tetsuo, 2015, Spratelloides atrofasciatus Schultz, 1943, a valid species of round herring (Clupeiformes: Clupeidae), Zootaxa 4028 (4), pp. 527-538 : 528-536

Spratelloides atrofasciatus Schultz, 1943

(English name: Small-banded Round Herring) (Japanese name: Ryukyu-kibinago)

(Okinawan local name: Baka-jyako, Sururu, Sururugwa) ( Fig. 1 A, B, Table 1 )

Spratelloides atrofasciatus Schulz 1943: 8 , fig. 1 (type locality: Fagasa Bay, Tutuila I., American Samoa); Schulz & Welander 1953: 27, Table 1 , fig. 7 (Bikini Atoll & Rongelap Atoll, Marshall Is.); Nishijimamoto 1963: 69, Table II, fig. 4 (Yonaguni I., Miyako I., Motobu, Okinawa I., Ryukyu Is.); Uyeno & Sato 1984, 1988: 19, pl. 337-G (Okinawa I.); Aonuma 2002: 244, (Okinawa I.).

Diagnosis. A species of Spratelloides with the following combination of characters: Dorsal fin rays 10–14; anal fin rays 10–13; pectoral fin rays 10–14 ( Fig. 3 ); vertebrae 43–47 ( Fig. 4 ) and lower gill rakers 20–24 ( Fig. 5 ); head length short 19.3–24.1% SL (mean 22.2%); upper jaw length short 7.0–9.3% SL (8.3%); snout length equal or slightly shorter than eye diameter, its length 5.9–7.4% SL (6.7%); lateral band usually wider than eye diameter, its width 5.7–7.9% SL (6.7%) ( Fig. 2 ); numerous black pigment spots on inner side of gill opening visible from the outside in preserved specimens ( Fig. 6 ).

Description. Counts and measurements of the holotype, paratype, and non-type specimens of Spratelloides atrofasciatus are given in Table 1 . Frequency distributions of selected counts (dorsal fin rays, pectoral fin rays, anal fin rays, total vertebrae, and lower gill rakers) are shown in Figs. 3–5 . Characters stated in the diagnosis are not repeated. Body elongated, subcylindrical, slightly compressed; body depth less than head length; snout pointed; eye diameter greater than interorbital width; upper jaw longer than snout; maxillary extending posteriorly to a vertical through front of eye but not through front of pupil; nasal openings separated by a dermal flap; two supramaxillae, the posterior with the lower part of the expanded portion larger than the upper part; lower jaw slightly projecting; gill rakers long and slender; pseudobranch with basal part of filaments covered by membrane; frontalparietal region smooth; posterior frontal fontanelles broadly divided anteriorly by a wedge of bone; rear of isthmus with usual notch and fleshy lobe on shoulder girdle; scale in lateral series from rear of head to base of caudal fin usually 42–45; vertical striae on scales discontinuous and posterior margin of scales not toothed; upper and lower lobes of caudal fin each with a pair of elongate scales on both sides; belly without scutes except a single W-shaped abdominal scute at the pelvic fin base; origin of dorsal fin equidistant between snout and caudal base or just nearer to snout than to caudal base; pelvic insertion under middle of dorsal fin base; anus immediately in front of anal fin origin; origin of anal fin a little closer to caudal fin base than to pelvic insertions.

Spratelloides atrofasciatus Spratelloides gracilis Color of preserved specimens: Head and upper and lower surfaces of body light brown; midlateral band blackish brown (silver outlined above by a thin blackish line when fresh); tip of snout, tip of lower jaw, dorsal surface of brain with black pigment, numerous black pigment spots on inner side of operculum visible from outside in preserved specimens ( Figs. 1 , 5 ); dorsal margin of iris with a black blotch in some specimens (not visible in the holotype and paratype); mid-dorsal line with a double row of black pigment cells from occiput to caudal fin base, the line irregular along base of dorsal fin; dorsolateral scale pockets fringed with black; ventral edge of abdomen pigmented; scales on caudal not pigmented.

Distribution and ecological notes. Schulz (1943) stated that the holotype of Spratelloides atrofasciatus was collected from Fagasa Bay, Tutuila Island, American Samoa. Schulz and Welander (1953) also reported S. atrofasciatus from Bikini, Rongelap and Rongerik Atolls, Marshall Islands. We collected specimens of S. atrofasciatus from the Ryukyu Islands: from south to north, Hatoma Island, Ishigaki Island, Miyako Island, Ohjima, Okinawa Island, and Takara-jima. A series of 24 specimens, NSMT-P 106605, 16.3–20.1 mm SL, from Palikoulo bay, Espiritu Santo Island, Vanuatu, 9 November 1964, collected by RV Shunyo, were identified as S. atrofasciatus in this study. Despite our two decades of search efforts, S. atrofasciatus is still not known from Kyushu (including Nagasaki, the type locality of S. gracilis ), Shikoku, nor Honshu, Japan. Thus the present known distribution of S. atrofasciatus is restricted to the Samoa, Marshall, Vanuatu, and Ryukyu Islands, and Takara Island in the Tokara Islands is the most northern distribution. Direct microscopic examinations of one specimen of URM-P 44245, 36.2 mm SL, 16 Aug. 2004; three stained and cleared specimens of URM-P 20001 32.7–37.9 mm SL, 1st June 1961; and one specimen of URM-P 44248, 45.2 mm SL, 17 July 2003, revealed they were gravid with 0.9–1.0 mm diameter ripe eggs. Maximum size of these specimens was 45.2mm SL and minimum mature size was 32.7 mm SL.

Comparisons. Spratelloides delicatulus and S. robustus are omitted from this comparison by lacking a lateral stripe and having continues striae on body scales. Striped round herrings, S. atrofasciatus , S. gracilis and S. lewisi , are similar to one another in general body appearance, especially in having a midlateral band and discontinuous vertical striae on their scales. Spratelloides lewisi is distinguishable from S. atrofasciatus and S. gracilis by having an incomplete midlateral band that fades anteriorly near the tips of the pectoral fins and in the number of lower gill rakers ( S. atrofasciatus : 20–24, S. lewisi : 28–32, S. gracilis : 30–39) ( Wongratana 1983; this study).

Spratelloides atrofasciatus is distinguished from S. gracilis in having a wider lateral band (5.7–7.9 % vs. 3.8– 7.5%SL), and shorter head length (19.3–24.1% vs. 20.8–26.9%), upper jaw length (7.0–9.3% vs. 7.7–10.5%) and snout length (5.9–7.4% vs. 6.6–9.0%) ( Fig.2 ), and fewer dorsal fin rays (10–14 vs. 12–14), anal fin rays (10–13 vs. 12–15), pectoral fin rays (10–14 vs. 12–14), total vertebrae (43–47 vs. 47–50), and lower gill rakers (20–24 vs. 30– 39) ( Figs. 3–5 ). Numerous black pigment spots on the inner side of the operculum are visible from the outside on preserved specimens of S. atrofasciatus that are absent in S. gracilis ( Figs. 1 AB and 6A).

Spratelloides atrofasciatus is a small species characterized by its minimum mature size of 32.7 mm SL and maximum size of 45.2 mm SL. By contrast, Shirafuji et al. (2007) reported mature S. gracilis from 54.9 mm SL and growing to 100.9 mm SL in Wakayama, Japan and Weng et al. (2005) reported mature S. gracilis from 54 mm FL (about 50 mm SL) and growing to 84mm FL (about 80mm SL) in Penghu, central Taiwan Strait. In this study, five stained and cleared specimens of S. gracilis (URM-P 17548, 39.1–49.5 mm SL) examined were not yet mature.

Discussion. Non-types of Spratelloides gracilis examined here share the same morphological characters with the lectotype of S. gracilis (RMNH 3260a, 94.0mm SL) ( Table 1 ).

Spratelloides atrofasciatus was originally described by Schultz (1943) based on two specimens. Although in his original description Schultz (1943) did not give detailed comparisons with congeners, Schultz and Welander (1953) mentioned the following diagnostic characters: fewer anal fin rays (10–11 vs. S. japonicus = S. gracilis : 12– 14), scales (41–42 vs. 44–49) and lower gill rakers (19–23 vs. 26–36), which distinguished it from Spratelloides japonicus (= S. gracilis ). Nishijimamoto (1963) reported the occurrence of S. atrofasciatus and compared it with the other two species, S. japonicus (= S. gracilis ) and S. delicatulus , found in Japan. Almost all specimens that Nishijimamoto studied are damaged or lost, but fortunately the samples of S. atrofasciatus collected from Miyako Island were salvaged. Those specimens were registered in our collection as URM-P 20000 and URM-P 20001 and used here.

Sprateloides gracilis was originally described by Temmick and Schlegel (1846) from specimens collected at Nagasaki, Japan. Boeseman (1947) designated the specimen RMNH 3060a as the lectotype of S. gracilis . Whitehead (1963) treated S. atrofasciatus as a subspecies of S. gracilis based on fewer counts of lower gillrakers (19–23 vs. 26–36) mentioned by Schultz and Welander (1953) and assumed the fewer counts of lower gillrakers representing an ecophenotypic variation of S. gracilis . Although Wongratana (1980) examined the holotype of S. atrofasciatus , he treated it as a junior synonym of S. gracilis because he found two specimens of S. gracilis with counts of fewer gill rakers from different areas of the Indo-West Pacific. Whitehead (1985) designated S. atrofasciatus as a junior synonym of S. gracilis by following Wongratana (1980). Whitehead’s (1963) study lacked direct examination of specimens of S. atrofasciatus . Two specimens showing counts of fewer gill rakers in Wongratana (1980) are here considered to be misidentifications of S. atrofasciatus , because those data all fall within our counts of S. atrofasciatus (see Fig. 42 in Wongratana, 1980).

We regard Clupea argyrotaeniata Bleeker, 1849 as a junior synonym of Spratelloides gracilis in having a larger number of lower gill rakers (31) and its larger body size (62.4mm SL), following Whitehead et al. (1966). Arambourg (1927) described a fossil species Spratelloides lemoinei from the Miocene, from Oran, northwestern coast of Algeria. In this study, we found that S. lemoinei is easily distinguishable from S. atrofasciatus by its larger size (82 mm SL) and larger number of anal fin rays (14). Gaudant (1979) and Grande (1985) treated S. lemoinei as a valid species, while Sorbini (1987) treated S. lemoinei as a junior synonym of S. gracilis . The relationships between S. lemoinei and S. gracilis are beyond the scope of this study.

Little is known about the biology and ecology of Spratelloides atrofasciatus . Schultz and Welander (1953) reported juveniles and male specimens with enlarged testes from Bikini Lagoon. In this study, minimum female maturation of S. atrofasciatus is 32.7 mm and maximum size is 45.2 mm SL. By contrast, Shirafuji et al. (2007) reported mature female S. gracilis from 54.9 mm SL and maximum size of 100 mm SL from Wakayama, Japan, and Weng et al. (2005) reported the first maturation size of female S. gracilis at 54 mm FL (about 50 mm SL) and maximum size about 90 mm SL from Penghu, central Taiwan Strait. These reports indicate that S. atrofasciatus matures at a smaller size and does not grow to the minimum mature size of S. gracilis . Milton et al. (1991) reported on the age and growth of S. gracilis from the Solomon Islands, near Samoa (the type locality of S. atrofasciatus ), and according to their study, S. gracilis showed two growth modes (slow and fast). From its estimated maximum size of 43mm SL, so-called ‘slow S. gracilis ’ were probably S. atrofasciatus and from its estimated maximum size of 60mm, so-called ‘fast S. gracilis ’ were probably S. gracilis . Thus, it appears that these two species are distributed sympatrically not only in the Ryukyu Islands, but also in the Solomon Islands.

Mohan and Kunhikoya (1985) reported S. japonicus (Houttuyn) (= S. gracilis ) matured from 45mm TL (about 39 mm SL) in Minicoy (formerly part of the Maldive Islands). Their study also seems to include S. atrofasciatus because of its small size at maturity.

Figures

FIGURE 1. (A) Original illustration of Spratelloides atrofasciatus (Fig. 1 in Schultz 1943): (B) holotype (USNM 115099, 31.7 mm SL) of S. atrofasciatus, photographed by Jennifer L Willett, Division of Fishes, Smithsonian Institution; (C) Original illustration of Spratelloides gracilis (PL CVIII fig. 2 in Temminck & Schlegel 1846) (right and left reversed); (D) Lectotype (RMNH 3260 a 94 mm SL) of S. gracilis, photographed by Seishi Kimura, Mie University.

FIGURE 2. Proportions of head length, greatest width of lateral band, upper jaw length, and snout length, in Spratelloides atrofasciatus (Holotype: solid circle, Non-types: open circles) and S. gracilis (Lectotype: solid triangle, Non-types: open triangles)

FIGURE 3. Frequency distributions of dorsal, anal and pectoral fin rays in Spratelloides atrofasciatus (solid) and S. gracilis (open), Holotype of S. atrofasciatus (solid circle), Lectotype of S. gracilis (solid triangle).

FIGURE 4. Frequency distributions of total vertebrae in Spratelloides atrofasciatus (solid) and S. gracilis (open). Holotype of S. atrofasciatus (solid circle).

FIGURE 5. Frequency distributions of lower gill rakers in Spratelloides atrofasciatus (solid) and S. gracilis (open). Holotype of S. atrofasciatus (solid circle).

FIGURE 6. Head and inner side of right gill cover in two species of Spratelloides. A S. atrofasciatus URM-P 44311, 41.4 mm SL. B S. gracilis, URM-P 44265, 52.4 mm SL.

Tables

TABLE 1. Meristics and proportional measurements expressed as percentage of standard length (SL), of the type and non-type specimens of Spratelloides atrofasciatus and S. gracilis. (Figures in parentheses indicate mean values; a = data from Schultz 1943; b = data from lectotype description of Boeseman 1947).

Holotype	Paratype	non-types	Lectotype	non-types
USNM 115099	USNM 115100	n = 110	RMNH 3260a	n = 105
Standard length (mm) 31.7 a Counts - dorsal-fin rays 11 a - pectoral-fin rays 12 a	30.5 a 12 a –	27.0–45.2 10–14 10–13	94.0 11 b 14 b	31.0–93.3 12–15 12–14
- pelvic-fin rays 8 a - anal-fin rays 11 a - lower gill rakers 21	8 a 10 a 19 a	8–9 10–14 20–24	8 b 14 b –	8 12–14 30–39
- scales 44 a - vertebrae 44 Measurements as % SL - head length 24 a - body depth 14.5 a - body width – - eye diameter 7.3 a	42 a – 24.3 a 14.7 a – 7.2 a	– 43–47 19.3–24.1 (22.2) 12.2–16.3 (14.0) 4.8–7.9 (6.2) 5.4–7.5 (6.3)	– – 21.2 – – –	– 47–50 20.8–26.9 (22.9) 11.6–18.2 (15.4) 4.8–7.3 (6.1) 4.4–8.6 (6.2)
- snout length 7.3 a - interorbital width 2.8 a - upper jaw length 8.8 a	7.2 a 2.9 a 9.8 a	5.9–7.4 (6.7) 3.1–5.2 (4.0) 7.0–9.3 (8.3)	7.2 – 8.1	6.6–9.0 (8.0) 3.2–4.9 (3.9) 7.7–10.5 (8.9)
- greatest width of lateral band – - predorsal length 45.7 a - prepectoral length –	– 47.5 a –	5.7–7.9 (6.7) 41.1–51.2 (47.0) 21.5–25.1 (23.3)	6.4 – –	3.8–7.5 (6.3) 46.4–50.9 (48.3) 21.3–28.2 (23.9)
- prepelvic length 52.1 a - preanal length 79 a - dorsal-fin base 9.5 a	53 a 81.3 a 9.8 a	49.7–58.4 (53.7) 76.2–83.5 (80.3) 7.9–12.6 (10.5)	– – –	53.6–58.9 (56.5) 77.5–84.6 (82.5) 8.4–12.3 (10.3)
- anal-fin base 9.5 a	9.8 a	8.3–13.6 (10.3)	–	7.9–11.8 (10.0)
- length of depressed dorsal fin 16.4 a	16.4 a	13.3–18.2 (15.9)	–	13.1–18.2 (15.5)
- length of depressed anal fin – - length from pectoral-fin insertion to 30 a pelvic-fin insertion - length from pelvic insertion to anal-fin 24.3 a origin	– 30.2 a 26.2 a	10.9–16.5 (13.9) 13.3–34.6 (30.2) 10.9–29.8 (26.5)	– – –	11.3–16.0 (13.7) 29.8–39.8 (33.5) 23.9–29.8 (27.0)