Sillago persica, Barani & Alavi-Yeganeh & Ghanbarifardi, 2025

Sillago persica sp. nov.

Fig. 2 View Figure 2 , Table 1 View Table 1

Type material.

Holotype: • TAC 1245 F ; 165 mm SL; sex unknown sex; Iran, Bushehr Province; 28°54'N, 50°46'E; Hashem Khandan Barani leg.; December 2021 GoogleMaps .

Paratypes: • TAC 1246 F ; 30 specimens, 114–195 mm TL, weight 11.6–35.9 g; Iran, Bushehr Province; located in the northern Persian Gulf, Iran ; Hashem Khandan Barani leg.; December 2021 .

Etymology.

The species name persica is derived from the Persian Gulf, where the type specimens were collected.

Diagnosis.

Dorsal fin with XI, I + 21–22 rays and anal with II (23–24) rays. The lateral line with 65–76 scales, 4–5 scale rows between the dorsal-fin origin and the lateral line. Gill rakers with 3 + 7–8 on the first gill arch. The vertebral formula with 14 or 15 abdominal vertebrae (predominantly 14), 4–5 predorsal vertebrae (mostly 4), and 14–15 caudal vertebrae (mostly 14), resulting in a total vertebral count of 32–34 (mostly 32) (Table 1 View Table 1 ). The body is characterized by the absence of dark blotches or a mid-lateral stripe. The swim bladder features two posterior extensions, with a duct-like process originating from the anterior end of the swim bladder and beginning at the junction of the roots of the two posterior extensions (Fig. 3 View Figure 3 ). Five wide extensions connect the posterior sub-extensions of the anterolateral extensions to the body of the swim bladder.

Description.

General body features are illustrated in Fig. 2 View Figure 2 , and counts and measurements are provided in Table 1 View Table 1 . The body is elongate, slightly conical at the anterior end, and tubular towards the posterior end. The body depth is 14.9 mm, 16.83 % of SL. The head is large, and its length is 26.3–28.7 % of SL. The snout is long, and its length is 38.2–45.8 % of HL. The eye is of moderate size, and its diameter is 15.3–17.6 % of HL. The interorbital region is flat, and its width is 17.9–21.1 % of HL. The mouth is small, terminal, and the tips of the upper and lower jaws are almost equal in length. Both jaws have a series of very small teeth that which form a broad band that tapers posteriorly into a single row. Gill rakers on the first arch are pointed and relatively large. The caudal peduncle is short; its depth is 77.5–90.1 % of the caudal-peduncle length. The body is covered in small to moderate-sized ctenoid scales, while the cheeks are covered in cycloid scales. The lateral line begins above the gill aperture and the anterior portion of the pectoral fin, extending along the dorsal edge to the end of the body.

The species has two separate dorsal fins, with rays as XI, I + 21 (range: 21–22), and the fin membrane has blurry black spots. The anal fin has II, 23 (range: 23–24) rays. The pectoral fin with 15 (15–16) rays. The pelvic fins are separate, wide, and have I + 5 rays, approximately triangular and smaller than the pectoral fins. The caudal fin has 16–18 rays.

Color of fresh specimens: the upper surface of the head is bright brown, while the trunk is also bright brown, transitioning to silver on the abdomen. The body lacks stripes, although the anterior half of the ventral side may exhibit some dark pigmentation. The dorsal fins are hyaline, featuring small dark spots on the fin membrane. The pectoral and pelvic fins are light yellowish hyaline; the anal fin is hyaline and free of dark spots, and the caudal fin is yellowish dusky, with a black margin along the posterior edge.

Swim bladder: the swim bladder is large and features two anterior extensions that extend forward to the basioccipital, which is positioned above the auditory capsules on both sides. Additionally, it has two posterior tapering extensions that reach into the caudal region without a lacuna between them. Two anterolateral extensions arise from the anterior portion of the swim bladder, each bifurcating into anterior and posterior sub-extensions. The anterior sub-extension consists of a short, simple, blind tubule, while the posterior sub-extensions are kinked, long, and complex at the beginning, becoming simpler and relatively thinner as they extend along the abdominal wall, ultimately terminating at the base of the posterior extensions. Notably, five wide extensions connect to these two sub-extensions, a feature that is not observed in other species within this genus. Furthermore, a single duct-like process originates from the pelvic surface of the swim bladder, extending to the urogenital opening. This duct-like process originates at the junction of the roots of the two posterior extensions, located anterior to the terminus of the swim bladder.

Distribution.

In this study, specimens of S. persica were collected from the northern Persian Gulf coast of Iran ( Bushehr) (Fig. 1 View Figure 1 ). The identified haplotypes formed a monophyletic group alongside the haplotypes of the G 5 clade of S. sihama , which were collected from the coast of Karachi, Pakistan ( Cheng et al. 2021). Thus, the known distribution of this species extends from the northern coast of the Persian Gulf to the northern coast of the Arabian Sea.

Comparison.

According to the subgenera grading system for the genus Sillago proposed by McKay (1985), S. persica is classified within the subgenus Sillago ( Sillago) due to the presence of two posterior extensions of the swim bladder. This study validates the recognition of S. persica as a new species through comparisons with all species in this genus. Distinctions among these species can primarily be made based on the meristic and morphometric characters outlined in Table 2 View Table 2 . The new species is immediately distinguished from others by below several key characters: it has a smaller head than S. megacephalus (26.35–28.71 % SL vs 33 %). It has more branched anal fin rays than S. parasihama , S. shaoi , S. muktijoddhai , S. nigrofasciata , and S. suezensis (23–24 vs 19–21). It has fewer scale rows between the lateral line and dorsal-fin origin than S. intermedius (4–5 vs 6–7) and a smaller head (26.3–28.71 % SL vs 30.0–31.0 %). It has fewer lateral line scales than S. parvisquamis (65–76 vs 79–84). It has fewer transversal scale rows than S. parvisquamis (4–5 / 8 – 10 vs 7 / 11–12). It has fewer a total of vertebrae than S. shaoi , S. parvisquamis , S. caudicula , and S. sinica (32–34 vs 35–40).

A comparison of swim bladder characteristics, a key trait for species diagnosis within this family, revealed that the swim bladder of S. persica is very similar to that of S. sihama , S. nigrofasciata , S. shaoi , S. muktijoddhai , and S. mengjialensis . However, notable differences exist. In S. shaoi and S. muktijoddhai , the roots of the two posterior extensions are non-adjacent, with a lacuna present between them, whereas in S. persica , S. nigrofasciata , S. mengjialensis , and S. sihama , the roots of the two posterior extensions are adjacent and lack a lacuna. Furthermore, the posterior sub-extension of the anterolateral extensions in S. persica is distinctive, characterized by a complex structure at its beginning, where five wide extensions connect to these two sub-extensions, a feature not observed in S. nigrofasciata , S. mengjialensis , and S. sihama . Additionally, the origin of the duct-like process in S. persica differs from that in S. parasihama and S. indica . In S. persica , the duct-like process originates anterior to the terminus of the swim bladder and before the junction of the roots of the two posterior extensions. In contrast, the duct-like process in S. parasihama and S. indica originates at the terminus of the swim bladder and arises at the junction of the roots of the two posterior extensions.

Furthermore, among the 12 known species of Sillago with two posterior extensions, S. persica can be easily distinguished from S. caudicula and S. intermedius based on body coloration, as both S. intermedius and S. caudicula exhibit dusky black spots on their bodies. It can also be differentiated from S. parvisquamis and S. sinica by the presence of dusky spots on the second dorsal-fin membranes, which show five or six rows in S. parvisquamis and three or four rows in S. sinica . Additionally, S. persica can be empirically distinguished from S. nigrofasciata , S. indica , and S. shaoi by the coloration of the anal fin: S. persica has a hyaline anal fin without black spots, whereas S. nigrofasciata typically has a yellowish anal fin with sparse black spots, and S. indica and S. shaoi have yellowish-brown anal fins with black dots on the interradial membranes. Moreover, S. indica , S. suezensis , and S. panhwari possess a faint midlateral stripe on their bodies, which is not present in S. persica .

Genetic analysis of the COI gene.

Sixrty-three sequences from Sillago species were utilized in the genetic analysis. The genetic distances among sillaginid species ranged from 0.05 to 0.26 K 2 P, while the genetic divergences within known species were between 0.00 and 0.01 K 2 P. The genetic distance between S. persica and other recognized Sillago species varied from 0.18 to 0.024 K 2 P. In comparison with the previous eight clades of the S. sihama complex, the genetic distance to clade G 5 was 0.01, while distances to the other eight clades were 0.18–0.20 (Table 3 View Table 3 ; Suppl. material 1). The Bayesian and maximum-likelihood phylogenetic tree based on COI gene sequences (Fig. 4 View Figure 4 ) indicated that the three haplotypes of S. persica and five haplotypes from the S. sihama clade G 5 ( MF 571946 View Materials ; Cheng et al. 2021) formed a monophyletic group. This clade is positioned as a sister group to a clade consisting of three haplotypes of S. indica and one haplotype of S. suezensis . Additionally, the three haplotypes from specimens identified as S. sihama in this study ( PV 523932 – PV 523934) clustered in a monophyletic group with those from S. sihama clade G 1 ( Cheng et al. 2021). The results from three species delimitation models ( ASAP, ABGD, and bPTP) further support the classification of S. persica haplotypes as a distinct species.