Abstract
Abstract Background Early life history traits of the temperate eel Anguilla japonica and tropical eel Anguilla marmorata were examined to determine the possible reason why these two species have similar spawning areas and oceanic larval transport in the North Equatorial Current and yet are recruited to different but partly overlapping continental growth habitats in northern East Asia. To understand the segregative migration of these two sympatric eel species, their glass eels were collected from nine estuaries in the Philippines, Taiwan, Japan, and China. The age at metamorphosis from leptocephalus to glass eel (T m), the age at estuarine arrival (T t), the time between metamorphosis and estuarine arrival (T t−m), and the growth rate (G t) of glass eels were calculated from daily growth increments in their otoliths. Results Results indicated that the G t was faster and the T m was younger in A. marmorata than in A. japonica. On the other hand, fish length and the T t at estuarine arrival were larger in A. japonica than in A. marmorata, indicating that elvers of A. japonica experience a longer oceanic drift than those of A. marmorata. In addition, the T t−m also indicated that A. japonica experienced a longer coastal migration than A. marmorata. Conclusion This study validated that the T m and G t seem to play important roles in the segregative migration and latitudinal distribution of these two sympatric freshwater eel species in the northwestern Pacific.
Highlights
Life history traits of the temperate eel Anguilla japonica and tropical eel Anguilla marmorata were examined to determine the possible reason why these two species have similar spawning areas and oceanic larval transport in the North Equatorial Current and yet are recruited to different but partly overlapping continental growth habitats in northern East Asia
Differences in size and age at estuarine arrival between species and among locations total lengths (TLs) of A. japonica glass eels at estuarine arrival ranged from 55.1 ± 1.9 mm in the Mingchiang River, southeastern China to 58.3 ± 11.3 mm in the Yalu River near the border of China and North Korea (Table 1), while those of A. marmorata ranged from 46.7 ± 1.7 mm in the Kurio River, southern Japan to 51.6 ± 1.6 mm in the Hsiukuluan River, eastern Taiwan
Anguilla japonica glass eels at estuarine arrival were significantly longer than A. marmorata (p < 0.001)
Summary
The age at metamorphosis from leptocephalus to glass eel (Tm), the age at estuarine arrival (Tt), the time between metamorphosis and estuarine arrival (Tt−m), and the growth rate (Gt) of glass eels were calculated from daily growth increments in their otoliths. Due to their mysterious life history and economic importance, freshwater eels (Anguilla spp.) have been the focus of much scientific research for decades. Life history information is very important because it is a key factor in understanding possible reasons for recruitment success or failure of anguillid eels and for their artificial propagation
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