Behavioral Diversity of Migration of the Japanese Eel Collected in the Yangtze River Based on Otolith Sr/Ca Ratios

Abstact: Yangtze River estuary is the main production area of Anguilla japonica in China. Japanese eel are distributed in the mainstream and many tributaries from the Yangtze River estuary to the upper Jinsha River extending as long as nearly 3000 km. However, their migration behaviors are rarely known. This paper analyzes the biological characteristics of a total of 153 specimens of silver eels collected from Jingjiang section of Yangtze River (31°30’N,120°42’E) from September to November of 2008 and tested the sagittal Sr/Ca ratios of 27 specimens. Among the 153 specimens, 85 are female and 68 are male with a female-male ratio of 1: 0.8. The ages of the females ranged from 3 to 7 years (average: 5.52) with the average total length (TL) of 669±80 mm, the average body weight(BW) of 555±229 g, the average condition factor(CF) of 1.77±0.22, and the average GSI of 1.32±0.31. The ages of the males ranged from 3 to 5 years (average: 4.38) with the average TL of 518±51 mm, the average BW of 234±76 g, the average CF of 1.62±0.18 , and the average GSI of 0.21±0.11. All such biological parameters of females are significantly larger than those of male specimens (P<0.05). According to the average Sr/Ca ratio 7.99±1.05(×10^-3)of the elver mark of sagitta, 17 individuals(62.96%) are river eels and 10 individuals(37.04%) are estuarine eels. Out of 16 females, 13 individuals(81.25%) are river eels and other 3 are estuarine eels whereas out of 11 males(36.36%) are river eels and 63.64% of them are estuarine eels. The analysis on Sr/Ca ratios for every growth layer group (GLG) indicates that: no significant difference can be seen between the second-age males and females. However, significant differences can be seen between the third-age, fourth-age, and migration-age males and female specimens. This should be contributed to the fact that the second-age eels of both sexes stay in relatively the same inhabitation waters. However, as they grow older, they begin to move to different place.