Evaluation of the population structure of Anguilla bicolor and A. bengalensis using total number of vertebrae and consideration of the subspecies concept for the genus Anguilla

Abstract

The population structures of two tropical species, Anguilla bicolor and Anguilla bengalensis, collected from several localities of each species range were evaluated using statistical analyses of total number of vertebrae (TV) data, which also included previously published data. There were significant differences in TV values between A. bicolor specimens from the Indian and Pacific oceans and between A. bengalensis specimens from the eastern and western Indian Ocean. These results suggest that A. bicolor is separated clearly into Indian Ocean and Pacific/ Indonesian Seas populations and A. bengalensis has eastern and western populations in the Indian Ocean, which both correspond to the historical subspecies designations of these eels. The existence of different spawning populations of other species such as the widely distributed tropical eel A. marmorata raises the question about how to categorise these subspecies or populations. Regardless of the taxonomic category used, each of these spawning populations should be considered to be a distinct ecological unit for conservation and sustainable management purposes.

Ecology and evolution of migration in the freshwater eels of the genus Anguilla Schrank, 1798

“…Thereafter, A. ancestralis was a synonym of A. celebesensis ( Castle and Williamson, 1974 ). Watanabe et al. (2014b) further determined that A. nebulosa nebulosa and A. nebulosa labiata are synonyms of A. bengalensis bengalensis Gray 1831 and A. bengalensis labiata Peters 1852, respectively.…”

“…Currently, nineteen species and subspecies of the genus Anguilla have been recognized ( Ege, 1939 ; Castle and Williamson, 1974 ; Watanabe et al., 2004 , 2009 , 2013 , 2014a , b ; Arai, 2016 ) ( Figure 1 ). Ege (1939) first classified the genus into nineteen species and subspecies, i.e., A. celebesensis Kaup, 1856; A. interioris Whitley, 1938; A. ancestralis Ege (1939) ; A. megastoma Kaup, 1856; A. nebulosa nebulosa McClelland, 1844; A. nebulosa labiata Peters, 1852; A. marmorata Quoy and Gaimard, 1824; A. reinhardtii Steindachner, 1867; A. borneensis Popta, 1924; A. japonica Temminck and Sclegel, 1846; A. rostrata Lesueur, 1817; A. anguilla Linnaeus, 1758; A. diefenbachii Gray, 1842; A. mossambica Peters, 1852; A. bicolor pacifica Schmidt, 1928; A. bicolor bicolor McClelland, 1844; A. obscura Günther, 1872; A. australis australis Richardson, 1841 and A. australis scmidtii Phillips 1925.…”

“…It is absolutely certain that the Indo-Pacific region is the original central location of speciation in anguillid eels. At present, most anguillid eels (13 species/subspecies) are distributed across tropical areas and six species/subspecies are found in temperate areas ( Ege, 1939 ; Castle and Williamson, 1974 ; Watanabe et al., 2004 , 2009 , 2013 , 2014a , b ; Arai, 2016 ). Although eel researchers pay more attention to temperate eels, studying the biological and ecological features of tropical eels will provide functional direction and a deeper understanding of anguillid eels in nature.…”

“…Nineteen species and subspecies of the genus Anguilla have been reported worldwide ( Ege, 1939 ; Castle and Williamson, 1974 ; Watanabe et al., 2004 , 2009 , 2013 , 2014a , b ; Arai, 2016 , Figure 1 ). Anguillid eels can be divided into “tropical eels” and “temperate eels” based on their geographical continental habitats ( Tesch, 1977 ).…”

Genetic identification method for two subspecies of the Indonesian short-finned eel, Anguilla bicolor, using an allelic discrimination technique

“…bicolor is further divided taxonomically into the two subspecies of Anguilla bicolor bicolor in the Indian Ocean and Anguilla bicolor pacifica in the western North Pacific and northern Indonesian Seas (Ege 1939;Watanabe 2003). These two subspecies, however, are almost identical in their morphological characteristics except for the mode of their number of vertebrate (Watanabe et al 2014), and only genetic characteristics enable them to be clearly divided into different subspecies. Currently, the most reliable information for distinguishing the two subspecies of A. bicolor is DNA nucleotide substitutions in a hypervariable region of the d-loop in their mitochondrial DNA (Minegishi et al 2012).…”