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International audience; ABSTRACT: The feeding ecology of leptocephali has remained poorly understood because they apparently feed on particulate organic matter (POM), which varies in composition, and it is unclear which components of the POM they assimilate. The δ13C and δ15N stable isotope (SI) and fatty acid (FA) compositions of 3 families of leptocephali and POM were compared in 3 latitudinal current zones of the western South Pacific. The δ15N signatures of leptocephali and POM overlapped, with both having their lowest values in the southern current zone. POM in general (across all zones) contained 38 FAs and was rich in saturated FAs (SFA) (16:0, 18:0, 14:0), while leptocephali contained 50 FAs, with high proportions of 16:0, and higher contributions of 22:6ω3, 20:5ω3, 18:1ω9, 16:1ω7 and other FAs than found in the POM. Serrivomeridae leptocephali in the north had higher δ15N signatures and were also distinguished from Nemichthyidae and Muraenidae larvae by their FA compositions (higher SFAs, lower 22:6ω3 and 20:5ω3). Although SI signatures of the Serrivomeridae larvae did not clearly vary with size, 16:0 and 18:0 FA proportions decreased with increasing larval size, and 22:6ω3 and 16:1ω7 increased in larger larvae. Correspondences between the latitudinal variations in nitrogen SI signatures and FA compositions of POM with those of leptocephali and the presence of FA markers of both autotrophic and heterotrophic organisms were consistent with leptocephali feeding on POM. POM can contain various materials from primary producers and heterotrophic microorganisms, but differences in the SI signatures and FA compositions in leptocephali remain to be explained through further research

In order to improve understanding of the larval migration and early life history charac- teristics of 4 tropical eels, Anguilla marmorata, A. bicolor pacifica, A. celebesensis and A. borneensis, the leptocephali, metamorphosing leptocephali and oceanic glass eels collected during 8 cruises in the western Pacific and Indonesian Seas from 1991 to 2002 were analyzed. The leptocephali of A. celebesensis and A. borneensis were collected only in close proximity to their relatively small spe- cies ranges in the Indonesian Archipelago and were found to have faster growth than the other 2 species with small-scale local migrations. The more widely distributed species A. marmorata and A. bicolor pacifica were collected in most sampling areas. Small leptocephali of A. marmorata were collected only to the west of the Mariana Islands, and only larger specimens, metamorphosing leptocephali, or oceanic glass eels of both species were collected in the Indonesian Seas. These distributions suggested that the 2 species have intermediate-scale migrations compared to other anguillid eels. The leptocephali of all 4 species appeared to reach a fully grown size of around 50 mm, which is considerably smaller than the maximum size of temperate anguillid leptocephali, and their growth was predominantly faster than that of temperate species. These data and recently derived molecular phylogenetic relationships among all anguillid species in the world suggest that the long spawning migrations of temperate eels evolved from much shorter migrations of tropical species, whose larval growth was faster and whose maximum larval sizes were smaller.