IDENTIFICATION OF FRESHWATER GOBY SPECIES FROM THE BIAK AND KOYOAN RIVERS, LUWUK BANGGAI, CENTRAL SULAWESI

Sulawesi is an island famous for its biodiversity, including many endemic species. In particular, Sulawesi has the highest number of gobies in the world, including species with potential as food and/or ornamental fishes. The exploration of freshwater ichthyofauna is important in the context of Indonesian and global biodiversity. This research aimed to identify gobies found in the Luwuk Banggai area of Central Sulawesi, as a contribution to the exploration of Indonesian ichthyofaunal biodiversity. Gobies were sampled from January to March 2019 in the Biak and Koyoan Rivers. The sampled fish were measured and identified based on morphological characteristics. A total of 52 specimens were collected, and identified as belonging to 17 species within two families, the Gobiidae and Eleotridae. Gobies from the Koyoan River comprised 32 specimens from 8 species, while 20 specimens belonging to species were found in the Biak River. Only two species were found in both rivers: Stiphodon semoni and Sicyopterus lagocephalus. These results augment the body of knowledge regarding the presence and distribution of gobies in Indonesia.


INTRODUCTION
Indonesia is a tropical country blessed with highly diverse flora and fauna, including ichthyofauna (Lamoureux et al., 2006;Hoffman et al., 2010;Hubert et al., 2015). As an archipelagic nation spread across three time zones and bisected by the equator, the freshwater ichthyofauna of Indonesia is concentrated in several of the larger islands, with a high mean species density of 0.6 species per 1000 km 2 (Hubert et al., 2015). To put this in perspective, two renowned biodiversity hotspots, Brazil and the Democratic Republic of the Congo, have freshwater ichthyofaunal densities of 0.37 and 0.48 species per 1000 km 2 , respectively (Hubert et al., 2015). The Indonesian Island of Sulawesi is particularly rich in endemic freshwater fishes. Kottelat (1990) lists 62 species of freshwater fishes found in Sulawesi, of which 52 are endemic to the island.
The gobies are a group of fishes with considerable, albeit often underestimated, potential as fisheries resources. In addition to their role as often locally important food fishes, many gobies also have potential as ornamental fishes, due to their attractive shapes and colouration. The City of Luwuk, capital of the Luwuk Banggai District in Central Sulawesi, is known as the watery city, because of the many rivers flowing into the sea all along the coast. Each of these rivers has its own ichthyofauna, including gobies. The aim of this research was to find and identify gobies living in the rivers of the Luwuk Banggai region of Central Sulawesi as a contribution towards the inventory of fish species richness and diversity in Indonesia. Specimens were collected using a scoop net. Each specimen was photographed (digital camera), euthanised and preserved in 70% alcohol. The specimens were identified to the lowest possible taxonomic level (species or genus) based on references inlcuding Carpenter and Niem (2001),  and FishBase, the global database of fishes (Froese and Pauly, 2019).

RESULTS AND DISCUSSION
The goby specimens found at the two study sites ( were only found in the Biak River ( Figure 2). This was likely related to the habitat types present, in particular the presence of muddy bottomed areas, a feature known as a favoured habitat criteria for the Eleotridae, in particular the members of this family commonly found in Indonesia. This habitat preference is described in Hubert et al. (2015) who found members of the Eleotridae in all the fresh water bodies they sampled in Indonesia.  All the species found in the Koyoan River (Figure 3) belong to the subfamily Sicydiinae. The Koyoan River is one of several rivers in the Luwuk Banggai area with waterfalls and rapids (Figure 4). Such features are known to be a habitat characteristic preferred by members of the subfamily Sicydiinae. According to Keith et al. (2003), during the upstream (amphidromous) migration of goby postlarvae, the majority of postlarvae stop and settle when they come to areas with waterfalls or rapids, which can provide them with ideal habitat. After adult gobies spawn in the river, the currents carry the embrios towards the sea where the larvae will undergo a planktonic larval phase. Once they reach the postlarval phase, the young gobies will migrate back towards rivers and streams to grow, mature, and spawn (McDowall, 2007;Keith et al., 2008).
Gobies of the subfamily Sicydiinae have a special adaptation, in the form of modified ventral fins, to enable them to climb up waterfalls. Their ventral fins are fused to form a sucker which enables them to attach themselves to rocks or other hard substrate. They use both their mouths and this sucker to climb upstream, making their way against strong, fast-flowing currents. Keith et al. (2003) report that the combination of these modified ventral fins and strong, well-developed pectoral fins can even enable goby species in the Sicydiinae subfamily to climb cliffs with fast-flowing waterfalls cascading down them. This ability enables members of the Sicydiinae subfamily to inhabit the upstream areas of watercourses, where they can be found in hilly or mountainous areas more than 100 m above sea level . According to Ebner et al. (2011), the Sicydiinae subfamily is a group of gobies with a high species diversity in the tropical Indo-Pacific region. The genus Schismatogobius comprises 24 known species worldwide (www.fishbase.org), 8 of which are found in Indonesia, with reported distributions in Sumatra, Java, Bali, Lombok, Ambon, and Sulawesi (Keith et al, 2017;Nurjirana et al., 2019). The species L. mekonggaensis found in the Koyoan River is a recently described species which was first found in 2014 in the Mekongga Mountains of Southeast Sulawesi Tenggara and has only been reported previously from that location (Keith et al., 2014). The species S. discordipinnis was originally found and described from Papua New Guinea by Watson (1995), and has since been reported from several other sites including Irian Jaya , Australia (Ebner et al.,2011), and the Solomon Islands (Boseto et al.,2007;Polhemus et al., 2008).
Out of the 17 species found in this study, only two species, S. semoni and S. Lagocephalus, were found in both the study sites. Keith et al. (2015) reports both S. semoni and S. lagocephalus as species which are widely distributed across Indonesia and even more widely within the Indo-Pacific region. In general, these gobies are relatively adaptable, which is one reason why they can be found in almost all aquatic habitat types in Indonesia, albeit with varying levels of abundance.

CONCLUSION
The results of this study show that the 52 goby specimens collected from the Biak River and Koyoan River in Luwuk Banggai, Central Sulawesi, Indonesia belong to 17 species. Research to explore the species diversity of freshwater fishes, in particular gobies, contributes to the body of knowledge on the species richness of Indonesian ichthyofauna. Such research has the potential to find new species as well as improving knowledge regarding the distribution of known species (new records).