Abstract
ABSTRACTFreshwater eels are one of the world’s most valuable cultured fish species. However, there is little information available on the biological characteristics of tropical anguillid eels genus Anguilla in the silver (maturation) stage even though these tropical eels account for two-thirds of all species in the genus. In order to understand the life history of tropical anguillid eels, Anguilla bicolor bicolor and A. bengalensis bengalensis which are found in Malaysian natural waters, age at maturation was studied. Their total length, body weight and maturation were significantly increased and advanced as their age became older. The ages at maturation (stages IV and V) of A. bicolor bicolor and A. bengalensis bengalensis ranged from 5.5 to 8.5 years and from 6.5 to 10.5, respectively. Ages of maturation in the tropical eels were earlier than that of other temperate eels A. anguilla, A. rostrata, A. australis and A. dieffenbachii, reported previously, although it was similar to that of the temperate eel A. japonica. The higher growth rate found in the tropical eels associated with the tropical habitat environment might induce the earlier maturation than the temperate species.
Highlights
The freshwater eel of the genus Anguilla, being catadromous, migrate between fresh water growth habitats and offshore spawning areas
Of the 13 species/subspecies found in tropical areas, 7 species/subspecies occur in the western Pacific around Indonesia and Malaysia, i.e. A. celebesensis (Kaup 1856), A. interioris (Whitley 1938), A. bengalensis bengalensis (Gray 1831), A. marmorata (Quoy & Gaimard 1824), A. borneensis (Popta 1924), A. bicolor bicolor (McClelland 1844) and A. bicolor pacifica (Schmidt 1928) (Ege 1939; Arai 2016)
Ages at maturation were similar for both Anguilla bicolor bicolor and A. bengalensis bengalensis
Summary
The freshwater eel of the genus Anguilla, being catadromous, migrate between fresh water growth habitats and offshore spawning areas. Nineteen species/subspecies of Anguilla have been reported worldwide, 13 of which occur in tropical regions (Ege 1939; Arai 2016). Of the 13 species/subspecies found in tropical areas, 7 species/subspecies occur in the western Pacific around Indonesia and Malaysia, i.e. A_celebesensis (Kaup 1856), A. interioris (Whitley 1938), A. bengalensis bengalensis (Gray 1831), A. marmorata (Quoy & Gaimard 1824), A. borneensis (Popta 1924), A. bicolor bicolor (McClelland 1844) and A. bicolor pacifica (Schmidt 1928) (Ege 1939; Arai 2016). Recent molecular phylogenetic researches on freshwater eels have revealed that tropical eels are the most basal species originating in the Indonesian and Malaysian region and that freshwater eels radiated out from the tropics to colonize the temperate regions (Minegishi et al 2005), suggesting that tropical freshwater eels must be more closely related to the ancestral form than their temperate counterparts. Studying the biological aspects of tropical eels provides clues for understanding the nature of primitive forms of life history in freshwater eels
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