Sri Lanka NATURALIST Vol : viii, No : 1-2, January - December 2015 A record of an estuarine goby Redigobius bikolanus (Perciformes: Gobiidae ) from inland freshwater body, Diyawanna oya in Sri Lanka W.H.T.Wijethunga Introduction Sri Lanka is a biodiversity hotspot, harboring a rich ichthyofaunal diversity consists of 93 indigenous freshwater fishes, of which 53 are considered as endemic (MOE, 2012; Batuwita et al., 2013). The family Gobiidae in Sri Lanka is represented by nine species; Awaous melanocephalus, Glossogobius giuris, Oligolepis acutipennis, Schismatogobius deraniyagalai, Sicyopterus griseus, Sicyopterus halei, Sicyopus jonklaasi, Stenogobius malabaricus and Stiphodon martenstyni where, Stiphodon martenstyni and Sicyopus jonklaasi are endemic (MOE, 2012). There are occasional records of estuarine gobies such as Rhino-horn Goby (Redigobius balteatus) have been reported from lowland freshwater bodies of the country (Pethiyagoda, 1991; De Silva et al., 2015). This short article reports another record of an estuarine goby belonging to the genus Redigobius from the lowland freshwater floodplains of Sri Lanka. Materials and Methods The study was carried out in the Kimbulawala Pahalawala wetland of Diyawanna Oya in Western Province. This site was situated approximately 8 km towards the inland with an altitude of 4 m above mean sea level. Fishes were sampled using a hand net (12 X 12 inches) along a stretch of 5 m in the stream. Standard length (SL) and Total length (TL) of individuals were measured using a measuring ruler (least count 1mm) and the external characters were photographed and illustrated. After the data collection and observations, all individuals were released to the same habitat where they were captured. Standard identification keys were used to identify the species (Larson, 2010). Figure 1: Location of the study site where Redigobius bikolanus was recorded Results and observations Two individuals of unknown goby species were observed live among the captured fish while sampling the bottom of the stream close to the bank of Kimbulawala, Pahalawela wetland nurtured by the Diyawanna oya (Figure 1). These samples were closely observed while keeping them in a small tank and their external characteristics were noted down. The body and head of the gobies were compressed with a terminal mouth and large eyes were located dorso-laterally on the head. The gape of the mouth was not extended beyond posterior margin of the eye. Head was appeared with curved irregular black bands from snout to posterior region of the eye (Figure 2a). They were dorsally dark brown to pale brown in color and laterally, there were diagonal black bars originating from the middle region of the body. Scale margins were outlined forming a network pattern. First dorsal fin was pointed with a large vertical black blotch similar to letter ‘C’ when laterally inverted (Figure 2b) and second dorsal Young Zoologists’ Association of Sri Lanka, National Zoological Gardens, Dehiwala. 62 Sri Lanka NATURALIST Vol : viii, No : 1-2, January - December 2015 A record of an estuarine goby Redigobius bikolanus (Gobiidae) from inland freshwater body, Diyawanna oya in Sri Lanka fin having 3-4 rows of dark spots above the base. Integument of the caudal fin and the anal fin hyaline was black tinted on the rays. Pectoral fin was hyaline. The body sizes of two specimens were 23 mm, 19 mm SL and 29 mm, 24 mm TL respectively. This goby species was identified as Speckled Goby (Redigobius bikolanus) according to the external characteristics and the standard keys. (Figure 3, Figure 4a, Figure 4b) Other freshwater fish species observed in the same locality during the survey were included Dwarf panchax (Aplocheilus parvus), Narrow line rasbora (Rasbora microcephalus), Silver barb (Puntius vittatus), Horadandiya (Horadandiya atukorali), Nile tilapia (Oreochromis niloticus), and Scribbled goby (Awaous melanocephalus). Figure 2a: Irregular black bands on head around the eye The habitat was an open habitat, fully exposed to sunlight with no canopy shade. Bottom of the stream consisted mainly of mud and sand with few pebbles. Aquatic plants covered the stream bank and depth of the stream was approximately 1- 2 feet. Discussion Redigobius bikolanus shows an abundant occurrence in Western Pacific region from Australia to Africa and known to occur in small freshwater streams and brackish water habitats such as mangroves. This species is considered as Least Concerned species according to the IUCN red list, 2012. R. bikolanus can be easily identified from R. balteatus in the same genus. A single broad black band extending downward and backward from first dorsal fin and a distinct black band extending from eye diagonally across opercle to lower edge of pectoral fin base are present in R. balteatus while these features could not seen in R. bikolanus specimens (Larson, 2010). However, R. bikolanus is known to be very variable and not easy to differentiate from its close congeners like R. nanus, R. oyens and R. tambujon. IUCN, (2012) and Larson (2010) has reported the presence of this species in Sri Lanka based on the examination of specimen collected by G. Duncker Figure 2b: Black blotch in first dorsal fin similar to letter “C” when laterally inverted in 1909 from Vakvella area (Galle, Southern Sri Lanka). The holotype of Stigmatogobius amblystoma is included among those specimens (ZMH 4635), 27.5 mm SL and (ZMH 7993), 2, 2527 mm SL. However, Deraniyagala (1952), Munro (1955), Pethiyagoda (1991), Goonatilake (2007) and Silva et al., (2015) have not listed this species from freshwater bodies of Sri Lanka. Figure 3: Illustration showing external characteristics of Redigobius bikolanus. (Drawing: Nethra Gomez) 63 Sri Lanka NATURALIST Vol : viii, No : 1-2, January - December 2015 A record of an estuarine goby Redigobius bikolanus (Gobiidae) from inland freshwater body, Diyawanna oya in Sri Lanka Figure 4a: Freshly caught Redigobius bikolanus (Photo: Vishwa Sachith) According to previous studies in Diyawanna oya, 43 species of freshwater fish (Perera et al., 2004) have been recorded, but Redigobius bikolanus had not been recorded previously. This site recording confirms the presence of the species in freshwater bodies of Sri Lanka. This species might have distribution throughout the lowland flood plains of the island, but further studies are required to confirm its distribution pattern and the seasonal occurrences. Acknowledgements I wish to thank Mr. A.A.T.Amarasinghe and Mr. Hiranya Sudasinghe (YZA) for their support in identification of the species. Mr. Jagath Gunawardana, Mr. Sameera Karunarathne (YZA) and Mr. Gayan Edirisinghe (YZA) are acknowledged for their valuable instructions in preparing this article. Mr. Devon Neranjan and Mr. Vishwa Sachith (YZA) were provided photographs. Miss Nethra Gomez (YZA) was provided illustrations. Miss. Lasanthi Wijayathunga (YZA), Miss. Iresha Harischandra (YZA) and Mr. Pradeep Gamsooriya Arachchi (YZA) are acknowledged for their support in various ways. References Batuwita, S., Silva, M., & Edirisinghe, U. (2013). A review of the danionine genera Rasboroides and Horadandia (Pisces: Cyprinidae), with description of a new species from Sri Lanka. Ichthyological Explorafion of Freshwaters, 24(2), 121-140. Deraniyagala, P.E.P. (1952). A colored atlas of some vertebrates from Ceylon, Volume one, Fish, Ceylon national museum, Colombo. 64 Figure 4b: Redigobius bikolanus colors faded after few minutes (Photo: Devon Neranjan) De Silva, M., Hapuarachchi, N., & jayarathne, T. (2015). Sri Lanka Freshwater Fishes, Wildlife conservation society, Galle, Sri Lanka. Goonatilleka, S.D.A. (2007). Freshwater Fishes of Sri Lanka, Bio diversity secretariat, Ministry of environment & natural resources, Sri Lanka. Larson, H. K. (2010). A review of the gobiid fish genus Redigobius (Teleostei: Gobionellinae), with descriptions of two new species. Ichthyolohgical Exploration. Of Freshwaters, 21( 2)-, 123-191. Larson, H. (2012). Redigobius bikolanus The IUCN Red List of Threatened Species 2012:e. T19388A2289216. (accessed on 3rd November 2015) http://dx.doi.org/10.2305/IUCN.UK.2012. RLTS.T19388A2289216.en MOE, (2012). The National Red List 2012 of Sri Lanka; Conservation Status of the Fauna and Flora. Ministry of Environment, Colombo, Sri Lanka. Munro, I.S.R. (1955). The Marine and Freshwater Fishes of Ceylon; Department of external affairs, Colombo. Pethiyagoda, R. (1991). Freshwater Fishes of Sri Lanka. Wildlife Heritage Trust, Colombo, Sri Lanka. Perera, W. P. N., & Perera, R.N. (2004). The Rich Diversity of Fish of the Diyawanna Oya Wetland System. Loris, 23(5&6):2004