By Sebastian Hüllen, ZFMK Bonn, Germany
Fishes are with a current number of 33,400 species (Froese & Pauli, 2016) the world's most diverse vertebrates. The Javanese ichthyofauna is said to be well known and comprises about 216 fresh and brackish water species (Hubert et al., 2015; Dahruddin et al., 2016). This number makes Java to the region with the highest density of fish species within the Sundaland ecoregion. But the diversity on Java is facing massive habitat loss and degradation due to overexploitation, pollution, and the growing population. Dahruddin et al. (2016) collected across the whole island with the attempt to provide DNA barcodes for all Javanese fish species. Surprisingly, they only got 77 of the 216 known species. But they also found additional 75 species, including 20 neozoans. Subsequently, their results show that the ichthyofauna of Java is far away from being well-known and reveal the consequences of the ongoing habitat lost and degradation.
The Mount Halimun Salak National Park is dissected by numerous small rivers and creeks forming the headwater regions of bigger streams. Nearly all waterbodies in the park can be considered as clear, fast flowing mountainous hill streams, which are often interrupted by waterfalls. Rachmatika (2003) published a book on the fish fauna of the national park and mentioned 50 species. However, just a few of her sampling locations lie within the park, so that only 5 species remain which are really known to occur in this area: Barbodes binotatus (Valenciennes, 1842), Glyptothorax cf. platypogon, Lentipes ikeae Keith, Hubert, Busson & Hadiaty, 2014, Sicyopus rubicundus Keith, Hadiaty, Busson & Hubert, 2014, and Tor tambra (Valenciennes, 1842).
During the two surveys to the Mount Halimun Salak National Park, we collected 860 individuals at 18 sampling locations within the park. These individuals belong to 8 orders, 13 families, and 20 species. The core ichthyofauna of the park consists of the following 10 species: The three cyprinids Barbodes binotatus, Rasbora aprotaenia Hubbs & Brittan, 1954, and Rasbora lateristriata (Bleeker, 1854) occur in the pelagic zones. At the shallow areas along the shore line these species are accompanied by the predatory snakehead Channa gachua Hamilton, 1822. The benthic zone is inhabited by four species of gobies (Lentipes ikeae, Sicyopterus macrostetholepis (Bleeker, 1853), Sicyopus rubicundus, and Sicyopus zosterophorum (Bleeker, 1856)) and two sisorid catfishes of the Genus Glyptothorax (Glypthothorax cf. platypogon 1+2). Both morphospecies differ in shape and coloration from its Sundaic congeners and might be new to science. Remarkably, gobies only occur in rivers, which run southwards to the Indian Ocean. These rivers, in contrast to the northwards running streams, were never connected to the ancient Sunda Rivers (Voris, 2000), which enables the colonization of the Sundaic Islands by primary freshwater fish species. So the gobies filled up the gap of the missing primary freshwater species and colonized the southwards running river from the sea. Based on species composition, a transition zone from upland to lowland habitats begins below 700 m altitude. Below this line, additional species occur which are especially known for lowland areas like the swamp eel Monopterus albus (Zuiew, 1793) and the fighting fish Betta picta (Valenciennes, 1846).