Occurrence of two closely related ricefishes, Javanese medaka (Oryzias javanicus) and Indian medaka (O. dancena) at sites with different salinity in Peninsular Malaysia

Abstract

Among ricefishes of the genus Oryzias, the Javanese medaka (O. javanicus) and the Indian medaka (O. dancena) are highly adaptable to seawater. Although wide distribution of the two species in the brackish waters of South and South-East Asia has been reported, their habitat preference remains unknown. We surveyed 12 sites in five estuarial areas of the west coast of Peninsular Malaysia from Kuala Gula to Tanjung Piai. Both species were found in all five areas, suggesting their distribution throughout the west coast of Peninsular Malaysia. This is the southernmostrecorded appearance of O. dancena, to the best of our knowledge. However, the habitats of the two species were essentially separated: of the 12 surveyed sites, the species were found in co-existence at only two sites, and one or the other species was found alone at the remaining 10 sites. We compared temperature, salinity, pH, and dissolved oxygen (DO) at the sampling sites and found that the habitat of O. javanicus is with higher salinity and DO. The salinity and DO at the sites of co-existence are near the lowest values found at the O. javanicus-only sites, and the highest values at the O. dancena-only sites. These results suggest that O. javanicus and O. dancena habitats are essentially separated; the former prefers hyperosmotic conditions while the latter prefers hypoosmotic conditions, and the latter may be more tolerant of hypoxia. The two sites of co-existence are points of contact between the species' separate distribution areas.

First record of the Javanese ricefish, Oryzias javanicus (Bleeker, 1854) (Beloniformes: Adrianichthyidae) in the natural waters of India

“…The habitat of O. javanicus in Muttukadu lagoon is similar to those observed in peninsular Malaysia (Yusof et al, ; Yusof, Ismail, & Rahman, ). In contrast, O. dancena prefers low‐saline regions, away from the main river, where water movement is restricted by vegetation (Yusof et al, ), and other typical freshwater habitats (Parenti, ); but O. carnaticus is also found in coastal, brackish as well as freshwater habitats (Parenti, ; Roberts, ). The distribution ranges of O. carnaticus, O. dancena, O. javanicus, and O. setnai in India is shown in Figure .…”

“…The species shows population‐level variations in their meristic counts (Table ). Oryzias javanicus is very similar to O. dancena and O. carnaticus , species that are native to the Indian subcontinent; but O. javanicus can be easily distinguished from the Indian species, by the presence of yellowish sub‐marginal bands on the dorsal and ventral sides of the caudal fin (Parenti, ; Yusof et al, ) (Figure ).…”

“…The Javanese ricefish, Oryzias javanicus (Bleeker, ), (Beloniformes: Adrianichthyidae) has a natural distribution in the brackishwaters of South East Asia from Peninsular Thailand, Malaysia, Singapore, Western Borneo and Indonesia east to Sulawesi and Lombok (Fricke, Eschmeyer, & Laan, ), and in Bangladesh (Ahmed, Islam, Sanzida, Akter, & Nahar, , Unpublished; based on sequences available in GenBank) (Figure ). Together with O. dancena , they are two of the most adaptable ricefish species, and highlighted as new experimental models (Imai, Koyama, & Fujii, ; Kang, Tsai, Liu, Lee, & Hwang, ; Parenti, ; Yusof, Ismail, Koito, Kinoshita, & Inoue, ). Here, we record for the first time, the occurrence of O. javanicus from natural waters in the south‐eastern coast of India, ~1,000 km away from its natural distribution range, and separated by the Bay of Bengal.…”

Expression Profiles of Branchial FXYD Proteins in the Brackish Medaka Oryzias dancena: A Potential Saltwater Fish Model for Studies of Osmoregulation

“…Among Oryzias species, the brackish medaka ( Oryzias dancena ) is native to brackish water (BW) environments, such as river mouths and estuaries [1], [2], [5], and exhibits better adult survival and hatching rates of fertilized eggs in hyperosmotic environments (i.e., seawater (SW)) as compared with the Japanese medaka ( O. latipes ) [3], [4]. Along with the zebrafish ( Danio rerio ), Japanese pufferfish ( Takifugu rubripes ), and spotted green pufferfish ( Tetraodon nigroviridis ), the Japanese medaka is an important model teleost with genomic sequences available for molecular studies.…”

Evolutionary implication of the absence of atrial natriuretic peptide (ANP) in euryhaline Oryzias fishes

“…Java medaka is especially more adapted to seawater; in our experience, breeding of Javanese medaka in seawater is easier than that in fresh water. Furthermore, wild Javanese medaka inhabits mangrove areas where salinity is relatively high (Shahrizad et al 2011). Thus, the genus Oryzias contains species with different degrees of seawater adaptability, ranging from stenohaline fresh-water species to euryhaline ones that prefer seawater.…”