Wednesday, September 16, 2015

[Ichthyology • 2015] Stiphodon palawanensis • A New Species of the Genus Stiphodon (Gobiidae: Sicydiinae) from Palawan, Philippines

Stiphodon palawanensis  Maeda & Palla, 2015
FIGURE 5. Males (ac) and females (e) of live Stiphodon palawanensis observed in Balsahan Stream, Puerto Princesa City (e, 18 May 2015; a, c, 19 May 2015).

Palawan is an island in the western Philippines, and the freshwater fish fauna of this island has received limited research attention. In the present study, a new goby species, Stiphodon palawanensis, is described on the basis of 57 specimens collected from freshwater streams on the island. This species can be distinguished from its congeners by having nine segmented rays in the second dorsal fin, 15 rays in the pectoral fin, a pointed first dorsal fin in males, premaxilla with 45–71 tricuspid teeth, the nape and posterior half of the occipital region covered by cycloid scales, 9–11 dusky transverse bars laterally on the trunk and tail, a line of black blotches (in male) or a black band (in female) on the distal part of the second dorsal fin, and the first dorsal and pectoral fins lacking distinctive markings. The new species has been found only on the Sulu Sea side of central Palawan. Three congeners, S. percnopterygionus, S. atropurpureus, and S. pulchellus have also been recorded from Palawan.

Keywords: Pisces, Stiphodon palawanensis, taxonomy, freshwater fish

FIGURE 5. Males (a, c) and females (e, f) of live Stiphodon palawanensis observed in Balsahan Stream, Puerto Princesa City (e, f, 18 May 2015; a, c, 19 May 2015).

Ecology. The new species was one of the dominant fish species observed in the middle reaches of Balsahan Stream (Puerto Princesa City) and Barake Stream (Aborlan) in May 2015. Stiphodon palawanensis inhabits pools with a substrate that is a mixture of boulders, gravel, and pebbles with exposed bedrock in some places. It also inhabits rapids. The water was clear. The fish were clinging to the rocks while feeding on algae. When disturbed, they swam to nearby rocks or hid in crevices under or between rocks. The maximum water depth of the sites was 1.5 m in May, but it could reach 3.0 m during the wet season. Normally, that occurs from June to December, while the dry season runs from January to May. In these two sites sampled, two cyprinid species Barbodes palavanensis (Boulenger) and Rasbora everetti Boulenger were very abundant with S. palawanensis. Other common species at these sites were two gobioids, Glossogobius illimis Hoese & Allen and Redigobius sp., and a halfbeak Dermogenys palawanensis Meisner.

Etymology. The name of the new species is derived from Palawan, the type locality, and the Latin suffix -ensis.

FIGURE 8. Stiphodon percnopterygionus (a) with Stiphodon palawanensis observed in Balsahan Stream, Puerto Princesa City, Palawan, on 18 May 2015.

Other Stiphodon species found in Palawan. During our two-day exploration in the type locality of the new species (Balsahan Stream in the Iwahig Prison and Penal Farm, Sulu Sea side of Puerto Princesa City) in May 2015, two other Stiphodon species were found; three female individuals of S. atropurpureus and one male individual of S. percnopterygionus Watson & Chen (Fig. 6). Two of the three S. atropurpureus individuals were collected (Fig. 7c) and listed as comparative material in this paper. Stiphodon percnopterygionus was not collected, however a wild individual was identified on site by snorkel based observation of characteristic markings of the body and fins (Fig. 8) and its unique, high triangular first dorsal fin. While S. palawanensis was very abundant, both S. atropurpureus and S. percnopterygionus were rare at this site.

Four Stiphodon specimens collected in the Iwahig River at Puerto Princesa City in 1988 have been deposited in the National Museum of Nature and Science (Ibaraki, Japan). The Iwahig is a relatively large river next to the Balsahan Stream. The specimens are composed of three S. palawanensis (NSMT-P 45091, 45092, and 45094) and one S. pulchellus (NSMT-P 45093), but the latter species was not found in our exploration in Balsahan Stream in May 2015.

In Barake Stream (Sulu Sea side of Aborlan), the only Stiphodon species found during our one-day exploration was S. palawanensis. All collections from Aborlan and Narra, examined in the present study (CMK and URM), also comprised entirely of individuals of S. palawanensis (Fig. 6). 

We also explored another river bearing the name Iwahig at Quezon, on the South China Sea side of the island (Fig. 6) in May 2015. Stiphodon pulchellus (Fig. 7a, b) was abundant, but S. palawanensis could not be found there.

Thus, the species composition of any Stiphodon assemblage seems to depend on the location on the island. Stiphodon palawanensis may be the dominant species in some areas, whereas S. pulchellus may be dominant in others. However, because only a small survey effort has been applied at each site and only a small part of the island has been explored so far, comprehensive surveys will be required to understand the distribution of Stiphodon species on Palawan.

Ken Maeda and Herminie P. Palla. 2015. A New Species of the Genus Stiphodon from Palawan, Philippines (Gobiidae: Sicydiinae). Zootaxa. 4018(3): 381–395. DOI: 10.11646/zootaxa.4018.3.3

FIGURE 5. Males (a–d) and females (e, f) of live Stiphodon palawanensis observed in Balsahan Stream, Puerto Princesa City (e, f, 18 May 2015; a, c, 19 May 2015) and Barake Stream, Aborlan (d, 15 May 2015).