The population structure of Anguilla bicolor bicolor was evaluated using their total number of vertebrae and genetic analyses of the mtDNA control region. Based on the likely geographic population structure of this subspecies in the Indian Ocean, the data were combined into East (Madras, Sumatra Island and Australia) and West groups (South Africa, Madagascar, Reunion and Seychelles) according to their sampling localities. Significant differences were not found in the range and mean total number of vertebrae between the East (N=74) and West groups (N=47) in the Indian Ocean, which were 107 to 113 (108.29±1.26), and 106 to 113 (109.60±1.47), respectively. Furthermore, the polymerase chain reaction-restriction fragment length polymorphism analysis for the mitochondrial control region using a total of 18 specimens from three localities showed no genetic differences between the East (N=14, Myanmar and Sumatra Island) and West groups (N=4, Madagascar) in the Indian Ocean. Morphological and genetic characters examined in the present study suggested no population structure for A. bicolor bicolor in the east and west side of the Indian Ocean, whereas they were ecologically assumed to be different populations. This contradiction suggested that these populations were in the beginning of speciation
