Japanese eel Anguilla japonica do not assimilate nutrition during the oceanic spawning migration: evidence from stable isotope analysis

Abstract

During 2008 and 2009, a total of 12 adult Japanese eels Anguilla japonica were captured in the southern part of the West Mariana Ridge, the presumed spawning area. We compared the sta- ble carbon and nitrogen isotope ratios (δ 13 C and δ 15 N) between the 'Mariana silvers' (terminal phase) and those of yellow and silver eels caught in rivers, lakes and coastal areas of Japan (initial phase). Profiles of stable isotope signatures between the initial and terminal phases were similar; both char- acteristically had a wide range for δ 13 C (-24.9 to -12.0‰ and -20.5 to -11.3‰ for the initial and terminal phases, respectively) and δ 15 N (6.5 to 18.4‰ and 9.0 to 18.1‰, respectively). Mesopelagic fishes, including several other anguillid species caught near the West Mariana Ridge, characteristi- cally had a very narrow range of δ 13 C (-16.9 to -15.3‰) and a wide but lower range of δ 15 N (5.3 to 11.1‰) than the Japanese eels. The very similar profiles in stable isotopic signatures between the initial and terminal phase eels, distinct from those of Mariana mesopelagic fishes, indicate that Japanese eels do not assimilate nutrition from the marine environment during long (ca. 6 mo) spawn- ing migration and retain the initial isotopic values of where they ceased feeding.