Fusigobius taipinensis, Chen & Chen & Yang & Harefa & Chou & Shen & Chang, 2024

Fusigobius taipinensis n. sp. Chen, Chen & Chang

( Figs. 1G–H View FIGURE 1 , 2 View FIGURE 2 , 3B View FIGURE 3 ; Tables 1–2 View TABLE 1 View TABLE 2 )

Materials examined. Holotype. NTOUP 2022-07 - 201 , 25.5 mm SL, coll. DY Hong and YC Yang, Taiping Island , South China Sea, July 27, 2022 . Paratypes. SOUTH CHINA SEA : NTOUP 2022-07 - 202 , 7 : 17.3–24.2 mm SL, coll. DY Hong and YC Yang, Taiping Island, South China Sea , July 27, 2022 . NTOUP 2022-07 - 203 , 2 : 28.8–29.8 mm SL, coll. DY Hong and YC Yang, Taiping Island, South China Sea , July 27, 2022 . NTOUP 2022-07 - 204 , 2 : 22.4–23.6 mm SL, coll. DY Hong and YC Yang, Taiping Island, South China Sea , July 29, 2022 . TAIWAN: NTOUP 2012-06 - 552 , 23.1 mm SL, Huapingyan, Liouciou Township , Pingtung County, 15 m. coll. I-S Chen et al., July 7, 2007 . NTOUP 2012-06 - 553 , 30.0 mm SL, Meirendong, Liouciou Township , Pingtung County, 15 m. coll. I-S Chen et al., July 8, 2007 . NTOUP 2012-06 - 554 , 2 : 17.8–23.1 mm SL, Huapingyan, Liouciou Township , Pingtung County, 15 m. coll. I-S Chen et al., July 10, 2007 . NTOUP 2012-06 - 555 , 25.7 mm SL, Huapingyan, Liouciou Township , Pingtung County, 15 m. coll. K-T Chen and Y-H Gong, August 24, 2011 . NTOUP 2012-06 - 556 , 28.8 mm SL, Huapingyan, Liouciou Township , Pingtung County, 15 m. coll. K-T Chen and Y-H Gong, August 24, 2011 . NTOUP 2012-06 - 557 , 28.4 mm SL, Shanfu fish port, Liouciou Township , Pingtung County, 15 m. coll. K-T Chen and Y-H Gong, August 24, 2011 .

Diagnosis. The new species can be distinguished from other congeners by the following unique combination of features: D1 VI; D2 I/9; A I/8; P 19; LR 25-26; SD1P 3. V with low frenum with lowest region about 1/10 of its spine; 4 th branched rays longest. Head and body with small, bright yellow round spots and some tiny white dots. A row of discontinuous yellow spots running from lower origin of orbit to upper lip. Cheek with a similar parallel row of yellow marks. Lateral midline with a horizontal series of 8–9 bright yellow spots, with size smaller than pupil on trunk. Caudal fin base with a median, triangularly yellow to grayish-yellow mark. First dorsal fin with a deep black blotch on upper 1/4 region in front of 3 rd spinous ray; a smaller oblong, deep black mark on upper half region in between 5 th and 6 th spinous rays. Second dorsal fin with 3–4 rows of tiny yellow round spots. Caudal fin translucent with three major radiated rows of small yellow spots.

Descriptions. Body proportions were listed in Table 1 View TABLE 1 . Body slender and elongate, compressed posteriorly. Cross-section of anterior part of head triangular. Snout short, pointed, dorsal profile smooth. Maxillary reaching the vertical of anterior margin of orbit. Anterior nostril as a short tube. Gill-opening extending ventrally beyond vertical of midline of opercle. Posterior nostril as round hole. VC 10+16=26.

Fins.—D1 VI; D2 I/9; A I/8; P 18-20 (modally 19); V I/5. No distinct elongate spinous ray in D1, with anterior three rays longer, rear tip extending to first branched ray of D2. An origin inserted below vertical of first branched ray of D2. P large, rear tip extending to vertical of second branched ray of D2. V with low frenum with lowest region about 1/10 of its spine length; 4 th branched rays longest, and rear tip extending beyond the anus. C rounded.

Scales.—LR 25-26 (modally 26); TR 7; PreD 0; SD1P 3. Body with median large ctenoid scales. Head including cheek, snout, nape and operculum naked. Prepectoral and prepelvic region with cycloid scales.

Head lateral-line system

Head canals: Three major canals comprise anterior oculoscapular canal, posterior oculoscapular canal, and preopercular canal. Head pores on anterior oculoscapular canal with a posterior nasal pore σ near each posterior nostril; a single median interorbital pore λ and posterior pore κ; a posterior pore ω just behind orbit; an infraorbital pore α below the posterior pore; a lateral canal pore β above preoperculum; a terminal lateral canal pore ρ above ear vertical of preoperculum. Pores θ and τ as two ends on posterior oculoscapular canal. Three pores γ, δ and ε on preopercular canal.

Sensory papillae: Cheek with four main longitudinal rows a, b, c, d. Row cp singular. More papillae in rows b and d. Row a divided into a1 (2 papillae), and a single a2. Operculum with rows ot and oi closely arranged; but well separated from row os. Row z vertically present. Rows x and y horizontally present. Nape with longitudinal rows g and m. Row f paired. Other papillae shown in Fig. 2 View FIGURE 2 .

Coloration while fresh. Body and head semi-translucent, head and body with small bright yellow round spots and some tiny white dots. A row of discontinuous yellow spots running from lower origin of orbit to the upper lip. Cheek with a similar parallel row of yellow marks. Pectoral fin base with two bright yellow round spots with a median white bar. Lateral midline with a horizontal series of 8–9 bright yellow spots with size smaller than pupil on trunk. Other part of trunk scattered with smaller yellow round spots. Caudal fin base with a median, triangularly yellow to grayish-yellow mark. First dorsal fin with a deep black blotch on upper 1/4 region in front of 3 rd spinous ray; a smaller oblong, deep black mark on upper half region in between 5 th and 6 th spinous rays; and its membrane with some smaller yellow spots and some grayish to black dots. Second dorsal fin with 3–4 rows of tiny yellow round spots. Pelvic somewhat translucent with tiny white dots. Anal fin with some small yellow spots on outer 2/3 region and some tiny white spots basally. Caudal fin translucent with three major radiated rows of small yellow spots.

Coloration in preservation. After 10% formalin preservation, all bright yellow spots and marks faded. Only the diagnostic feature of the first dorsal fin, along with separate black marks, remained.

Distribution. This new species is mainly found in Taiping Island in the South China Sea, with some populations also in southern Taiwan. Its presence may extend the known range of new species to other regions of the South China Sea, southern Japan, or the tropical Indian Ocean.

Etymology. The specific name, taipinensis , refers to its type locality, Taiping Island, which is the largest island belonging to Taiwan ROC, located around the Nansha Islands in the South China Sea. The new species identified is more dominant than any other Fusigobius species collected from the island. This region may also serve as an important habitat for the current species. In contrast, although the species is also found in southern Taiwan, it is actually a very rare species compared to all other species observed among the members of its congeners.

Remarks. The new species herein is rather similar to the typical F. duospilus in terms of its meristic features. However, it can be well distinguished from F. duospilus from the type locality of the holotype by (1) the different pigmentation in anterior half of first dorsal fin as higher black blotch vs. vertical black stripe ( Fig. 3 View FIGURE 3 ); (2) body coloration: a series of bright yellow spots vs. 4 main grayish brown blotches; (3) great differentiation in mitogenetic comparison ( Fig. 4 View FIGURE 4 ). Hoese and Reader (1985) describe specimens of fish not from Australia exhibiting a similar dorsal fin pattern, which could possibly be identical to those in our studies.

Phylogenetic insights into Fusigobius species in Taiwan. The phylogenetic analysis of all Taiwanese species of Fusigobius was inferred from the partial sequences of the mtDNA ND5 gene represented in Fig. 4 View FIGURE 4 . Both phylogenetic trees showed similar topologies, except the divergence time of Bathygobius was different between the trees. In the PhyML tree, Bathygobius separated from the common ancestor with all analyzed Fusigobius species, and Fusigobius formed a monophyletic group. As for the Bayesian tree, Bathygobius separated from the common ancestor with F. melacron and other Fusigobius species. All these scenarios could explain the plesiomorphic state of F. melacron and the monophyletic group of remaining Fusigobius that shares the synapomorphic feature of separated pelvic fins. All recognized Taiwanese species, including F. humeralis , F. inframaculatus , F. melacron , and F. neophytus , were very well separated by long branches with rather high posterior probability and bootstrap value support. The intraspecific genetic divergence of all Fusigobius species was very low. The phylogenetic trees were also well supported by the fact that F. taipinensis n. sp. was different from its closely related F. duospilus with a high posterior probability and bootstraps value. All the species delimitations also supported that these two lineages were distinct species; even the ASAP method assigned E. acanthopoma and E. oxycephala as the same species, irrespective of which substitution models were selected.

With the new species Fusigobius taipinensis and the new record Fusigobius melacron documented in this study, a total of six species of Fusigobius have been formally recorded from Taiwan. These reef gobiids were morphologically and genetically distinguished.