ABSTRACT
Freshwater eels of the genus Anguilla Schrank (1798) consist of 16 species, three of which are further divided into two subspecies (Ege 1939; Castle and Williamson 1974; Watanabe 2003; Watanabe et al. 2004, 2005, 2009a, 2013, 2014a,b). All of these species make oceanic migrations at various scales from a few hundred to thousands of kilometers (Arai 2014). They are globally distributed in temperate, tropical, and subtropical areas and are considered to be prevalent nearly worldwide, except for the land masses adjacent to the South Atlantic and the eastern Pacifi c oceans (Ege 1939). They all have a catadromous life-history strategy, spawning in remote tropical seas with larvae that are transported back by currents to their nursery grounds in freshwater or coastal areas. Tesch (2003) divided the freshwater eels into tropical and temperate species according to their geographic distributions. The tropical and temperate eels consist of 11 and 5 species, respectively. The basic biology of temperate eels is generally known, but information about the tropical eels that comprise two-thirds of all anguillid eel species is much more limited. A recent molecular genetic study indicated that the genus Anguilla originated in the deep ocean (Inoue et al. 2010). Furthermore, studies have revealed that tropical eels are the most basal species originating in the Indonesian region and that freshwater eels radiated out from the tropics to colonise the temperate regions (Minegishi et al. 2005).
