Sillago nigrofasciata, Xiao & Yu & Song & Gao, 2021

Xiao, Jia-Guang, Yu, Zheng-Sen, Song, Na & Gao, Tian-Xiang, 2021, Description of a new species, Sillago nigrofasciata sp. nov. (Perciformes, Sillaginidae) from the southern coast of China, ZooKeys 1011, pp. 85-100 : 85

Sillago nigrofasciata sp. nov. Figures 1 , 2 , 3 , 4 , Tables 1, 2, 3

Type material.

Holotype. OUC_FEL178001, 151.2 mm SL, coastal area of Fuding, Fujian Province, China, collected by Yuan Li, January 2014.

Paratypes. OUC_FEL178002-178030, 29 individuals, 134.4-161.4 mm SL, collection data same as for holotype; ZJOU_FEBL021255-021283, 29 individuals, 127.8-155.6 mm SL, coastal area of Xiamen, Fujian Province, collected by Jia-Guang Xiao, November 2015; ZJOU_FEBL021284, 1 individuals, 167.6 mm SL, coastal area of Changhua, Taiwan, collected by Shih-Chieh Shen, July 2014; OUC_FEL178051-178068, 18 individuals, 147.8-161.4 mm SL, coastal area of Zhuhai, Guangdong Province, collected by Bin-Bin Shan, December 2014; OUC_FEL178069-178098, 30 individuals, 120.3-163.0 mm SL, coastal area of Fangchenggang, Guangxi Province, collected by Dong-Ping Ji, December 2014.

Etymology.

The specific name Sillago nigrofasciata is a compound adjective derived from the Latin words referring to the wide mid-lateral black longitudinal band of this species, a diagnostic character of the species.

Diagnosis.

Relatively large body and usually with a wide mid-lateral black stripe from opercular to caudal peduncle; dorsal-fin rays X-XII (mostly XI), I+20-22, soft anal fin rays 20-22; scales in lateral line 67-75, scales above lateral line 4-6; gill rakers 2-4+5-8; vertebra: abdominal 14 or 15 (mostly 14), modified 3-7 (mostly 4 or 5), caudal 13-18, and total 34 or 35 (mostly 34) (Table 3 ). Swim bladder with two posterior extensions, the origin of the duct-like process at the terminus of swim bladder and start at the joint of roots of two posterior extensions (Fig. 4 ).

Description.

General body features are shown in Figure 3 . Counts and measurements are given in Table 3 . Body elongate, anterior slightly pyramidal, posterior cylindrical; anterodorsal profile smooth. Body depth 16.1% (13.4-17.4%) in SL. Head large, length 29.9% (25.1-30.8%) in SL. Snout long, 41.7% (39.6-52.7%) of HL. Eye moderate, its margin slightly covered with adipose eyelid, diameter 17.9% (16.5-24.9%) of HL. Interorbital region flat, interorbital width 23.5% (14.8-31.2%) of HL. Nostrils situated anterior to upper margin of eye; posterior margin of anterior nostril with single anteriorly directed flap; posterior nostril lacking flap. Mouth small, terminal, anterior tip of upper jaw situated at almost same position as tip of lower jaw. Upper jaw with small canines forming a wide tooth band becoming narrower posteriorly. Lower jaw with small canines, forming tooth band anteriorly, width same as upper jaw tooth band, tooth band gradually becoming narrower posteriorly, ending in one row. Palatine and tongue toothless. Vomer with three to four rows of canine teeth. Posterior margin of preopercle slightly serrated. Gill aperture large, lateral, extending to ventral side of head, stopping at middle bottom of opercle. Gill rakers on the first arch pointed but short. Caudal peduncle short, depth of caudal peduncle 61.0% (51.3-88.5%) of length of caudal peduncle.

Body covered with small or moderate sized ctenoid scales, and cheek scales cycloid, arranged in two or three rows. Lower part of pre-opercular-mandibular canal covered with cycloid scales. The base of pectoral fin and ventral fin lacking scales. Lateral line beginning above gill aperture and anterior portion of pectoral fin, extending along curve of dorsal edge to the end of body.

Two separated dorsal fins, first dorsal fin XI (X-XII), obviously higher than second, origin posterior to top of pectoral fin base, composed of spines, gradually shortening. Fin membrane with dense black spots. Base of second dorsal fin long, composed of a single spine and 21 (20-22) soft rays, originating mid-body, and not extending to caudal fin origin when placed flat. Origins of anal fin slightly posterior to cloacal pore, with II+22 (20-22), not extending to caudal fin origin when placed flat. Pectoral fin 16 (14-16), slender. Two separated ventral fins broad, I+5, approximately triangular, and shorter than pectoral fin.

Color of fresh specimens.

Upper surface of head dark brown and trunk bright brown, grading to silver on abdomen. Dorsal side of snout brownish gray. Cheek yellow, slightly silver posteriorly, with black dots amassed on the anterior inferior part of eyes. A wide faint stripe composed of tiny black dots on skin always present, from opercular to caudal peduncle. Dorsal fins yellowish hyaline, small dark dense spots on fin membrane. Pectoral, ventral, and anal fins yellowish hyaline with dark spots; caudal fin yellowish dusky with a black margin and grayish brown margin posteriorly, lobes usually broadly truncated posteriorly.

Swim bladder.

Swim bladder large. Two anterior extensions diverging to terminate on either side of the basioccipital above the auditory capsule. Two posterior tapering extensions of the swim bladder penetrating into the caudal region, one usually longer than the other. Two anterolateral extensions originate anteriorly, each branch into anterior and posterior sub-extensions: the anterior one comprising a short, simple blind tubule and the posterior sub-extensions kinked, long and complex, extending along the abdominal wall ventral to the base of the posterior extensions, respectively, tangent but not interconnected. A single duct-like process originating from ventral surface of swim bladder extending to the urogenital opening and a sub-extension connecting with a sanguineous vesicle close to vertebra, of unknown function. Eight or nine lateral processes extending from entire lateral surface of main body of swim bladder, anterior three or four stout and horn-like, posterior five or six small and triangular in shape.

Habitat.

Habitat is similar to S. sihama in nearshore areas and frequently entering estuaries for considerable periods, it is common along the beaches, sand bars, and mangrove creeks with sandy substrates. Depths ranging from 0 to 20 m, and frequently captured by trawling vessels.

Distribution.

Sillago nigrofasciata sp. nov. was only found along the southern coast of China including the coastal waters of the South China Sea and the Taiwan Strait. Actually, its distribution range is similar to that of S. sihama in China (Fig. 1 ).

Comparisons.

According to the subgeneric grading system in Sillago proposed by McKay (1985), we used the characters of swim bladder, especially, the number of the posterior extensions, to divide Sillago into several categories. This study confirmed the validity of a new species with two posterior extensions by comparison-elimination with other species in the same category. Among the ten known members of Sillago with two posterior extensions, S. nigrofasciata sp. nov. was easily distinguished from S. intermedius and S. caudicula by the body coloration (dusky black blotches were present on the body of S. intermedius and S. caudicula ), from S. parvisquamis and S. sinica by the dusky spots on the second dorsal fin membranes (five or six rows in S. parvisquamis and three or four rows in S. sinica ). Empirically, S. nigrofasciata sp. nov. could also be distinguished from S. sihama , S. indica , S. panhwari , and S. suezensis by the coloration of anal fin (the anal fin of S. nigrofasciata sp. nov. was usually yellowish with sparse black spots, the anal fin of S. indica was yellowish brown, but the anal fin of S. sihama , S. panhwari , and S. suezensis were hyaline; on the other hand, there were more black dots on skin and fins of S. indica than on S. nigrofasciata sp. nov. when fresh).

Moreover, by the primary diagnostic features (Table 1 ), S. nigrofasciata sp. nov. was easily distinguishable from other species by the following: S. megacephalus by having a smaller head (25.1-30.8% SL in S. nigrofasciata sp. nov. vs. 33.0% in S. megacephalus ) and less soft rays in anal fin (20-22 in S. nigrofasciata sp. nov. vs. 23 in S. megacephalus ), from S. parvisquamis and S. sinica by having 34-35 total vertebrae (39-40 in S. parvisquamis and 37-39 in S. sinica ), from S. parvisquamis and S. sinica can also by having 67-75 scales on lateral line (79-84 in S. parvisquamis and 75-79 in S. sinica ), and from S. caudicula by gill rakers (4/11 in S. caudicula ) and soft rays in anal fin (23-24 in S. caudicula ).

As for the shape of swim bladder (Fig. 4 ), that of S. suezensis was always controversial ( Kaga 2013). Based on its original description, the figures of the swim bladder ( Golani et al. 2014: 418, fig. 4A-C) were stylized, lacking the details of those provided by McKay (1985, 1992) and Kaga and Ho (2012). However, the sequences of S. suezensis (Mediterranean population) and S. sihama (Hong Kong and southern Red Sea populations) showed a strong genetic divergence ( Tikochinski et al. 2013). Here, those sequences were also cited to verify authenticity of S. nigrofasciata sp. nov. and dismissed S. suezensis (Fig. 2 ). The swim bladder of S. panhwari was described as having narrow anterior extensions joined at the origin, diverging to terminate on both sides of the basioccipital above the auditory capsule whereas the two posterior extensions penetrate into the caudal region, one usually longer than the other, and with a duct-like process ( Panhwar et al. 2018). But based on the photo ( Panhwar et al. 2018: fig. 3a), the swim bladder was flat and gasless, and the anterolateral extensions may be broken. Moreover, there was no description of the swim bladder of S. megacephalus by Lin (1933).

Sillago sihama was considered as having a wide Indo-Pacific distribution and consisting of more than one taxon. McKay (1992: 59, fig. 130) described two swim bladder patterns of S. sihama in the FAO Catalogue based on a Red Sea specimen and a Queensland specimen, with markedly different shapes and concomitant geographical divergence. The swim bladder of S. nigrofasciata sp. nov. was very similar to that of S. sihama and S. shaoi , but there were still some differences: the roots of two posterior extensions in S. shaoi were non-adjacent, the two posterior extensions were not well-knit in its natural state, and there was a lacuna between the two posterior extensions; the origin of the duct-like process was at the terminus of the swim bladder and between the roots of two posterior extensions. However, on the swim bladder of S. nigrofasciata sp. nov. and S. sihama , the roots of two posterior extensions were adjacent and two posterior extensions were in close proximity; and the difference between them was the origin of the duct-like process of S. nigrofasciata sp. nov. at the terminus of the swim bladder and starting at the joint of the roots of two posterior extensions, but the origin of the duct-like process of S. sihama was anterior to the terminus of the swim bladder and anterior to the joint of the roots of two posterior extensions. Moreover, the swim bladder of S. indica had the same framework as that of S. nigrofasciata sp. nov. excepting the thin simple anterolateral extensions (vs. S. nigrofasciata sp. nov., anterolateral extensions were twisted, long, and complicated). Sillago nigrofasciata sp. nov. could also be easily distinguished from S. intermedius and S. caudicula by those swim bladders with simple anterolateral extensions; S. parvisquamis stood out as having the strongest anterolateral extensions in comparison with the others (Fig. 4 ).

Figures

Figure 1. Sampling sites and corresponding sample sizes (represented by circle size and Arabic numerals) of Sillago nigrofasciata sp. nov. HN, Hainan Island; TW, Taiwan Island; FD, Fuding; XM, Xiamen; ST, Shantou; ZH, Zhuhai; ZJ, Zhanjiang; BH, Beihai; FCG, Fangchenggang; DZ, Danzhou; HK, Haikou; CY, Chiayi; CH, Changhua.

Figure 2. A Sillago nigrofasciata sp. nov., OUC _ FEL 178001, holotype, 151.2 mm SL, Fuding, China, B Sillago sihama, ZJOU _ FEBL 021131, 131.0 mm SL, Zhangzhou, China.

Figure 3. Swim bladders of nine Sillago species A S. nigrofasciata sp. nov. B S. sihama C S. shaoi D S. sinica E S. indica F S. parvisquamis G S. intermedius (McKay 1992) H S. caudicula (Kaga et al. 2010) I S. suezensis (sketch based on Golani et al. 2014). AE, anterior extension; ASAE, anterior sub-extension of anterolateral extension; PSAE, posterior sub-extension of anterolateral extension; LP, lateral processes; DLP, duct-like process; PE, posterior extension. Black arrows indicate differences between S. nigrofasciata sp. nov. and S. sihama.

Figure 4. Neighbor-joining (NJ) tree for cytochrome oxidase subunit I (COI) gene sequences of eight species of Sillago. The NJ tree was constructed under the K 2 P model using Sillaginodes punctata as the outgroup. Bootstrap support values of> 70 % from 1000 replicates are shown.