Sillago (Sillago) shaoi Gao and Xiao, 2022

Grzelak, Katarzyna & Sørensen, Martin V., 2022, Echinoderes landersi Grzelak & amp; Sørensen 2022, sp. nov., Zoological studies 55 (47), pp. 1-10 : 3-9

Sillago (Sillago) shaoi Gao and Xiao , sp. nov.

urn:lsid:zoobank.org:act:19B9174E-23EE-4A55-9ED1-4E0C9FDCE2D9 ( Fig. 2 )

Holotype: FEMBL 150001, 182.2 mm SL, coastal area of Xiamen, Fujian Province, China, collected by Yuan Li, December 2013.

P a r a t y p e s: FEMBL 150002-150016, 15 individuals, 173.0- 203.3 mm SL, collection data same as for holotype; FEMBL 150017-150019, 3 individuals, 146.2-167.6 mm SL, coastal area of Changhua County, Taiwan, collected by Shih-Chieh Shen, July 2014; FEMBL 150020-150039, 20 individuals, 182.0-216.0 mm SL, coastal area of Dongshan, Fujian Province, China, collected by Yuan Li, April 2014. All specimens were deposited at the Fishery Ecology & Marine Biodiversity Laboratory, Fishery College, Zhejiang Ocean University (Zhoushan, China).

Etymology: The specific name “shaoi ” was named in honor of the taxonomist Dr. Kwang-Tsao Shao for his remarkable contribution in classification of fishes.

Diagnosis: A new species of the genus Sillago and differs from other Sillago species with a relatively larger body size; the 1st dorsal fin S. shaoi sp. nov. has XI (not to XII), the 2nd dorsal fin with I and 20-22 soft fin rays; 21-22 soft anal fin rays; scales in lateral line 70-73, scales above lateral line 5 or 6; gill rakers 3-4+5-6; vertebra: abdominal 13-14 (mostly 14), modified 4-6 (mostly 5), caudal 15-17 (mostly 16), and total 35. Apparent differences among shape of swim bladders of the 9 Sillago species (with two posterior extensions of the swim bladder) showed S. shaoi sp. nov. had a similar swim bladder with S. sihama but differed in detail ( Fig. 3 ). Genetic analysis also showed strong interspecific differentiation among the six Sillago species with two posterior extensions of the swim bladder and other five Sillago species in coastal waters of China ( Table 2).

Description: General body features were shown in figure 2. Counts and measurements were given in table 3. Description was based on the holotype, data of paratypes were shown in parentheses when variation was recognized between holotype and paratypes.

Body elongate, anterior slightly pyramidal, posterior cylindrical; anterodorsal profile smooth. Body depth 17.1% (13.4-17.9%) in SL. Head large, length 28.3% (26.1-31.0%) in SL. Snout long, 46.6% (41.8-50.2%) of HL. Eye moderate, its margin slightly covered with adipose eyelid, diameter 21.3% (14.9-24.1%) of HL. Interorbital region flat, interorbital width 27.0% (17.5-27.0%) of HL. Nostrils situated anterior to upper margin of eye; posterior margin of anterior nostril with single anteriorly directed flap; posterior nostril lacking

(G)

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 first arch pointed but short. Caudal peduncle short, depth of caudal peduncle 71.7% (56.6-88.9%) of length of caudal peduncle.

Body scales deciduous, size moderate, ctenoid except for those on prenasal area, which were cycloid. Cheek scales deciduous, cycloid, arranged in about two or three rows. Lower part of pre-opercular-mandibular canal covered with cycloid scales. Pectoral fin base and ventral fin base lacking scales. Lateral line beginning above gill aperture and anterior portion of pectoral fin, extending along curve of dorsal edge to end of body.

Two separated dorsal fins, 1st dorsal fin XI, higher than 2nd one obviously, origin posterior to top of pectoral fin base, composed of spines, gradually shortening. Fin membrane with dense black spots. Base of 2nd dorsal fin long, composed of 1 spine and 20 (20-22) soft rays, originating midbody, and not extending to caudal fin origin when placed flat. Origins of anal fin slightly posterior to cloacal pore, with II + 21 (21-22), not extending to caudal fin origin when placed flat. Pectoral fin 16 (16-18), slender. Two separate ventral fins broad, I+5, roughly triangular, and shorter than pectoral fin. Comparisons of meristic characters of nine Sillago species with two posterior extensions of the swim bladder were shown in table 1.

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 slightly silver, with black dots massed on the anterior inferior part of eyes. A wide faint stripe composed of tiny black dots on skin sometimes present, from opercular to caudal peduncle. Dorsal fins yellowish-hyaline, small dark dense spots on fin membrane. Pectoral, ventral, and anal fins yellowish with dark spots; caudal fin yellowish dusky with a black margin and grayishbrown 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 anditory 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 were kinked, long and complex, extending along the abdominal wall ventral to the peritoneum 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 was present connecting with a sanguineous vesicle close to vertebra, with 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 rather 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, sandbars and mangrove creeks with sandy substrate. In depths ranging from 0 to 20 m, and frequently captured by trawling vessels.

Distribution: Sillago shaoi sp. nov. was presently only found in coastal waters of the Taiwan Strait, larvae and juveniles of this species were found in the estuarine area of the Tamsui River (25.20°N, 121.38°E) in northern Taiwan (provided by Dr. Kwang-Tsao Shao) ( Fig. 1 ).

Comparison

According to the subgenera-grading system in genus 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; and confirmed the validity of a new Sillago species with two posterior extensions by comparison-elimination other species in the same category. Among the eight known members of Sillago with two posterior extensions, we could easily distinguished S. shaoi sp. nov. 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, we could also distinguish S. shaoi sp. nov. from S. sihama , S. indica and S. suezensis by the coloration of anal fin (the anal fin of S. shaoi sp. nov. was usually yellowish, the anal fin of S. indica was yellowish-brown, but the anal fin of S. sihama and S. suezensis were hyaline; on the other hand, there were more black dots on skin and fins of S. indica than on S. shaoi sp. nov. when fresh).

Moreover, by the primary diagnostic features ( Table 1), S. shaoi sp. nov. was easily distinguishable from others by the following: S. megacephalus by having a smaller head (26.1- 31.0% SL in S. shaoi sp. nov. vs. 33.0% in S. megacephalus ) and soft rays in anal fin (21-22 in S. shaoi sp. nov. vs. 23 in S. megacephalus ), from S. intermedius , S. parvisquamis , S. sihama , S. suezensis and S. sinica by having 35 total vertebrae (34 in S. intermedius , S. sihama , S. suezensis ; 39-40 in S. parvisquamis and 37-39 in S. sinica ), from S. parvisquamis and S. sinica by having 70-73 scales on lateral line (79-84 in S. parvisquamis and 75-79 in S. sinica ), from S. indica , S. suezensis and S. sihama by having 3-4/5-6 gill rakers (3-4/ 7-8 in S. indica , 3-4/ 8-10 in S. suezensis and 3/ 8-9 in S. sihama ), and from S. caudicula by gill rakers (4/ 11 in S. caudicula ) and soft rays in anal fin rays (23-24 in S. caudicula ) ( Table 1).

As for the shape of swim bladder ( Fig. 3 ), S. suezensis was always controversial ( Kaga 2013). Judging from its original description based on the holotype: the figures of the swim bladder ( Golani et al. 2014: 418, Fig. 4 , A-C) were stylized; lacked 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. shaoi sp. nov. and dismissed S. suezensis ( Fig. 4 ).

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 shape and concomitant divergence. The swim bladder of S. shaoi sp. nov. was very similar to that of S. sihama but there were still some differences: the roots of two posterior extensions in S. shaoi sp. nov. were non-adjacent, 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 terminal of swim bladder and between the roots of two posterior extensions. However, on the swim bladder of S. sihama , the roots of two posterior extensions were adjacent and two posterior extensions were in close; the origin of the duct-like process was anterior to the terminus of swim bladder and anterior to the joint of roots of two posterior extensions. Swim bladder of S. indica had the same framework with S. shaoi sp. nov. excepting the thin-simple anterolateral extensions (vs S. shaoi sp. nov., anterolateral extensions were kinky, long and complicated). S. shaoi could also be easily distinguished from S. intermedius and S. caudicula by those swim bladder with simple anterolateral extensions; S. parvisquamis standed out with the strongest anterolateral extensions in comparison with the others ( Fig. 3 ).

Recently, Gao et al. (2011) described a new Sillago species - S. sinica from the East China Sea without describing the shape of the swim bladder, the most important characteristic for identifying Sillaginids. Here, the swim bladder of S. sinica was described for the first time and its subgeneric status was reassigned. Compared with other Sillago species with two posterior extensions of the swim bladder, S. sinica was unique ( Fig. 3 ). Two anterior extensions extending forward and diverging to terminate on each side of the basioccipital above the anditory capsule. Two posterior tapering extensions of the swim bladder penetrating into the caudal region, one usually longer than the other. Two anterolateral extensions commencing anteriorly, each branch into anterior and posterior sub-extensions: the anterior one comprising a simple blind tubule, extending forward and usually slightly longer than anterior extensions; the posterior sub-extensions were unique with some stunted blind tubule, unilateral and outward; the posterior sub-extensions extending along the abdominal and about onethird of the body of swim bladder in length; a single duct-like process present.

Genetic analysis of the COI gene

Forty-nine specimens of 11 Sillago species were used in the genetic analysis. After sequence alignment, a 583 bp fragment of the COI gene was obtained. There were no indels/insertions, and 207 variable sites were observed. Pairwise genetic distances (K2P) were shown in table 2. Genetic distances among Sillago species ranged from 0.123 to 0.239. The NJ tree based on COI gene sequences ( Fig. 4 ) revealed that all previously recognized and the newly discovered S. shaoi sp. nov. individuals formed monophyletic groups. The new species S. shaoi sp. nov. and S. sinica were clustered firstly. Furthermore, a strong genetic divergence was detected between S. shaoi sp. nov. and its plesiomorphic species - S. sihama .

Figures

Fig. 2. Sillago shaoi Gao and Xiao, sp. nov., FEMBL150001, holotype, 182.2 mm SL, Zhoushan, China.

Fig. 3. Swim bladders of 7 Sillago species. (A) S. shaoi sp. nov., (B) S. sihama, (C) S. sinica, (D) S. indica (Kaga and Ho 2012), (E) S. parvisquamis (McKay 1992), (F) S. intermedius (McKay 1992), (G) S. caudicula (Kaga et al. 2010). 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.

Fig. 1. Sampling sites of Sillago shaoi sp. nov. The open circle represents the Tamsui River estuary.

Fig. 4. Neighbor-joining (NJ) tree for cytochrome oxidase subunit I (COI) gene sequences of 11 species of Sillaginidae. The NJ tree was constructed under the K2P model using Sillaginodes punctata as outgroup. Bootstrap support values of> 50% from 1000 replicates are shown.