The false Indian anchovy, Stolephorus advenus Wongratana, 1987 (Engraulidae), previously known only from the type specimen from the Northern Territory, Australia, is redescribed herewith and its validity confirmed, on the basis of the holotype and nine additional specimens from the northern coast of Australia. Although the significance of differences between S. advenus and some congeners with a similarly short maxilla has been unclear, the diagnostic reliability of some characters, including melanophores absent on the dorsal- and anal-fin bases, pectoral fin and occipital region, fewer pseudobranchial filaments, and greater number of prepelvic scutes, is confirmed. An extended distribution of the species around the northern coast of Australia is also reported.

Clupeomorpha, ichthyofauna, Stolephorus balinensis, Stolephorus indicus, taxonomy

Stolephorus Lacepède, 1803, an Indo–Pacific genus of marine and/or brackish water anchovies (Engraulidae), comprises 45 valid species (Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a, 2018b, 2018c, 2018d, 2021a, 2021b, 2021c, 2022a, 2022b, 2023; Hata et al. 2019, 2020a, 2020b, 2021, 2022a, 2022b, 2023; Gangan et al. 2020). Although the genus was previously considered congeneric with the morphologically similar genus Encrasicholina Fowler, 1938 (e.g., Whitehead 1967, 1972; Wongratana 1983), the two genera were separated by Nelson (1983) and Whitehead et al. (1988), with Lavoué et al. (2017) later proposing that Stolephorus represented the earliest generic offshoot within Engraulinae. Stolephorus advenus Wongratana, 1987 (false Indian anchovy) has been known to date only from the holotype, collected from Cobourg Peninsula, Australia, and was, in all respects, very poorly known.

During an examination of Australian species of Stolephorus, nine additional specimens of S. advenus, collected from several localities along the northern coast of Australia, were identified. The specimens, with additional morphological and biological information confirming the validity of the species, are described in detail herein.

Counts and measurements follow Hata and Motomura (2017), and are presented as percentage of standard length or head length. All measurements were made with digital calipers to the nearest 0.1 mm. “Pelvic scute” refers to the scute associated with the pelvic-fin insertion, whereas “prepelvic”, “postpelvic”, and “predorsal scutes” refer to the scutes anterior to the pelvic scute, posterior to the pelvic scute, and just anterior to the dorsal-fin origin, respectively. Abbreviations are as follows—SL is the standard length; UGR, LGR, and TGR are the rakers on upper limb, lower limb, and total gill rakers, respectively, with associated numbers indicating the specific gill arch; and SMX-MX is the distance between posterior margins of supramaxilla and maxilla. Institutional abbreviations follow Sabaj (2020).

Comparative material examined. Stolephorus balinensis (Bleeker, 1849), 119 specimens, 43.4–148.4 mm SL: listed in Hata and Motomura (2023) and 15 additional specimens: BBM-ICH 1963-1348-38, 3 specimens, 84.1–99.3 mm SL, Muar, Johor Strait, Malaysia; BPBM 19216, 2 of 5 specimens, 98.4–102.0 mm SL, Ambon, Indonesia; BPBM 26469, 2 specimens, 86.0–94.2 mm SL, Cebu Island, Philippines; BPBM 29883, 2 specimens, 124.8–125.3 mm SL, Montong, west coast of Lombok, Indonesia; CAS 230421, 1 of 4 specimens, 91.7 mm SL, southwest of Babelthuap Island, Palau (07°23′17′′N, 134°30′40′′E), 2–6 feet (approx. 0.6–1.8 m) depth; CAS 235774, 99.9 mm SL, 1 of 3 specimens, mouth of Mae Nam Prasae River, Rayong (12°41′45′′N, 101°42′11′′E); CAS-SU 29219, 4 specimens, 84.1–89.9 mm SL, Palau.

Stolephorus belaerius Hata, Lavoué et Motomura, 2021, 27 specimens, 63.4–127.1 mm SL: listed in Hata et al. (2021) and 2 additional specimens: CAS 58503, 97.3 mm SL, Mombasa, Kenya; LACM 31618-18, 76.3 mm SL, 1 of 5 specimens, Hasini Creek, Manda Island, Kenya.

Stolephorus commersonnii Lacepède, 1803, 16 specimens, 62.1–112.3 mm SL: listed in Hata et al. (2021).

Stolephorus horizon Hata et Motomura, 2023, 34 specimens, 62.3–108.1 mm SL; Stolephorus indicus (van Hasselt, 1823), 41 specimens, 53.3–133.6 mm SL; Stolephorus meteorum Hata, Lavoué, Bogorodsky, Alpermann, et Motomura 2023, 20 specimens, 49.2–115.0 mm SL; Stolephorus scitulus (Fowler, 1911), 46 specimens, 47.6–102.7 mm SL: listed in Hata and Motomura (2023).

Family Engraulidae

Stolephorus Lacepède, 1803

Stolephorus advenus was described by Wongratana (1987a) based on a single specimen (holotype), collected from Cobourg Peninsula, Australia (Fig. 1A). Although the original description stated that the holotype had five prepelvic scutes and 24 1LGR, re-examination of the specimen confirmed the presence of seven prepelvic scutes and 25 1LGR. The pelvic fin was also missing from the holotype, but Wongratana (1987a) speculated that when depressed, the pelvic fin of S. advenus would not have reached the vertical through the dorsal-fin origin. The additional specimens examined in the presently reported study confirm the validity of that speculation. Although Wongratana (1987a) and Wongratana et al. (1999) stated that S. advenus lacked melanophores on the occipital region, some of the additional specimens actually have melanophores scattered on that region (Fig. 1F). Furthermore, following their revisional studies of Stolephorus, Whitehead et al. (1988) and Wongratana et al. (1999) indicated that S. advenus could be distinguished from all congeners, except Stolephorus indicus, by the short maxilla (posteriorly not reaching the preopercle posterior margin) and 1LGR fewer than 30. However, since those studies, numerous new or cryptic species of Stolephorus have been described, with Whitehead’s et al. (1988) “Stolephorus indicus” actually representing at least seven species, Stolephorus balinensis, Stolephorus belaerius, Stolephorus commersonnii, Stolephorus horizon, Stolephorus indicus, Stolephorus meteorum, and Stolephorus scitulus. Accordingly, S. advenus can be presently distinguished from all other congeners, except the latter seven species previously regarded as “S. indicus”, by having a shorter maxilla (see above), 1LGR fewer than 30, the pelvic fin not reaching posteriorly the vertical through the dorsal-fin origin, and no dark lines on the dorsum. In addition, S. advenus differs from all seven species previously included in “S. indicus” as follows: maxilla not reaching posteriorly anterior margin of preopercle, 13.7%–14.5% of SL [vs. just reaching or slightly beyond anterior margin; longer than 15% of SL (14.3%–17.5% in S. balinensis)]; no melanophores scattered along bases of dorsal and anal fins, or on entire pectoral fin [vs. melanophores present along bases of dorsal and anal fins, and on upper part of pectoral fin (no melanophores on pectoral fin of S. horizon)]; ventral scutes 6 or 7 [vs. 5 or fewer (rarely 6 in S. balinensis and S. meteorum)], and pseudobranchial filaments 15–18 (vs. 19 or more). Furthermore, the shorter head of S. advenus (21.6%–22.9% of SL) separates it from S. horizon (22.6%–25.2%), S. indicus (23.0%–26.7%), and S. meteorum (23.7%–26.0%). The body depth of S. advenus (17.4%–20.9% of SL) is greater than that of S. commersonnii (14.2%–17.8%) and S. scitulus (14.6%–16.9%), the pectoral fin is longer (13.5%–14.2% of SL in S. advenus) than in S. balinensis (11.3%–13.9%), and the pelvic fin is shorter (7.6%–8.0% of SL in S. advenus) than in S. belaerius (7.9%–10.3%) (Whitehead et al. 1988; Wongratana et al. 1999; Kimura et al. 2009; Hata and Motomura 2018a, 2018b, 2018c, 2018d, 2021a, 2021b, 2021c, 2022a, 2022b, 2023; Hata et al. 2019, 2020a, 2020b, 2021, 2022a, 2022b, 2023; Gangan et al. 2020; this study; Fig. 3).

Figure 1. 

Specimens of Stolephorus advenus [A: holotype, NTM S. 10031-153, 72.2 mm SL, Cobourg Peinsula, Northern Territory, Australia (photograph taken by S. Tashiro); B: lateral, C: dorsal, and D: ventral views of non-type specimen, NTM S. 13803-003, 49.1 mm SL, Clarence Strait, Northern Territory, Australia (melanophores absent on occipital region); E: lateral view of whole body and F: dorsal view of head of non-type specimen, CSIRO CA 2688, 79.6 mm SL, Gulf of Carpentaria, Northern Territory (melanophores scattered on occipital region); scale bars indicate 0.5 mm].

Figure 2. 

Distributional records of Stolephorus advenus based on specimens examined in this study (red star: type locality; red dot: non-type specimens).

Figure 3. 

Maxilla length (A), head length (B), body depth (C), pectoral-fin length (D), and pelvic-fin length (E) (all as % of standard length; SL) relative to SL in Stolephorus advenus (red circles), S. balinensis (blue triangles), S. belaerius (gray stars), S. commersonnii (purple hexagons), S. horizon (green squares), S. indicus (yellow diamonds), S. meteorum (dark blue inverted triangles), and S. scitulus (orange crosses).

Although the known distribution of the species was limited to the type locality (Cobourg Peninsula, Northern Territory, Australia), both Whitehead et al. (1988) and Wongratana et al. (1999) suggested that S. advenus may be distributed (hence question marks on their distribution maps) along the northern coast of Western Australia and the Gulf of Carpentaria. Such a distribution is partially confirmed in the presently reported study (Fig. 2), since there are still no specimens recorded in Western Australia. The biology or habitat of S. advenus is also still totally unknown. Whitehead et al. (1988) and Wongratana et al. (1999) presumed that the species is coastal pelagic, and schooling. The collection of some of the specimens described here in coastal waters 14.6–18 m depth is indeed suggestive that the species is coastal. Based on the standard length of the holotype, Whitehead et al. (1988) and Wongratana et al. (1999) also suggested a maximum standard length of 7.2 cm, which is slightly shorter than the largest specimen (CSIRO CA 2688, 79.6 mm SL) measured in the present study.

We are especially grateful to N. Bailly (BC), A. Suzumoto and L. O’Hara (BPBM), D. Catania and M. Hoang (CAS), A. Graham and J. Pogonoski (CSIRO), M. Nakae (NSMT), and B. Russell, M. Hammer, and G. Dally (NTM) for opportunities to examine specimens of Stolephorus. We also thank S. Tashiro (formerly KAUM), T. Clardy (LACM), and T. Munroe, K. Murphy, D. Pitassy, L. Willis, and A. Reft (USNM) for their curatorial assistance, and G. Hardy (Ngunguru, New Zealand), for checking an early version of the manuscript. This study was supported in part by the Sasakawa Scientific Research Grant from the Japan Science Society (28-745); a Grant-in-Aid from the Japan Society for the Promotion of Science for JSPS Fellows (DC2: 29-6652); JSPS KAKENHI Grant Numbers 19K23691; and JSPS Overseas Research Fellowships (202160519).