Biometric variations among populations of Carnatic ricefish (Oryzias carnaticus, Jerdon, 1849), a native larvivorous fish of South India

The possibility of any biometric variations in Oryzias (ricefish) populations present in three geographically isolated drainages around the city of Chennai, India were studied. Though biometric characters were insufficient to differentiate the three populations as distinct species, the dorsal and anal fin ray counts had shown considerable variation from the baseline information reported earlier besides, certain scale counts were significantly different among as well as between the populations. Branched pelvic fin ray counts (6-7) of Sriperumbudur population was different from the baseline information (6). The anal fin rays of saline inhabitant population were higher compared to those in freshwater. Furthermore, as most of the baseline meristic variables overlap from one species to another, identification of Oryzias carnaticus and Oryzias dancena need not be solely based on the meristic characters. The application of biometrics has limitations in identifying this species and molecular techniques may resolve the taxonomic ambiguity of Oryzias species in the Indian subcontinent.