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To understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early‐stage larvae were distributed south of or near the salinity front, confirming that the salinity front is an important oceanic feature to understand spawning locations of the Japanese eel. Larger size larvae tended to distribute into higher latitudes. Transport to northern latitudes with their growth would facilitate transport into the Kuroshio region, but retention in the Subtropical Countercurrent (STCC) might be detrimental. Preleptocephalus isotope ratios reflected maternal ratios, but feeding‐stage leptocephali (8–56 mm) tended to have higher ∂15N values at lower latitudes typically in areas south of a salinity front. Feeding larvae quickly assimilate isotope ratios from the NEC after spawning and early growth. Large differences of ∂13C values of larvae between the NEC and STCC might vary with spatial baselines in the two currents. However, diel vertical migrations should be considered, because the isotope ratios in particulate organic matter distinctly depend on the depth. Comparisons among Japanese eel larvae and other taxa of leptocephali in the NEC illustrate the need for further studies on the trophic ecology of leptocephali. [ABSTRACT FROM AUTHOR]

Anguilla japonica leptocephali are transported from their offshore spawning area to their recruitment areas in East Asia, but their depth distributions, food sources and feeding are still poorly known. This study analyzed carbon and nitrogen stable isotope ratios of leptocephali of A. japonica, Ariosoma major and Ariosoma spp., and of particulate organic matter (POM), their likely food source, at five different depths in 2004-2009. We used mixing models to show that A. japonica appeared to be feeding at depths between 5 and 50 m, but sometimes deeper. A. major appeared to have a tendency of mostly feeding at depths of 50 m or shallower. Although the A. japonica and Ariosoma spp. collected in the same area during the leptocephalus stage appeared to have different feeding ecologies possibly related to different types of POM, their different depth distributions, sizes and transport histories may also help explain these differences. [ABSTRACT FROM AUTHOR]