Abstract
Eel larvae apparently feed on marine snow, but many aspects of their feeding ecology remain unknown. The eukaryotic 18S rRNA gene sequence compositions in the gut contents of four taxa of anguilliform eel larvae were compared with the sequence compositions of vertically sampled seawater particulate organic matter (POM) in the oligotrophic western North Pacific Ocean. Both gut contents and POM were mainly composed of dinoflagellates as well as other phytoplankton (cryptophytes and diatoms) and zooplankton (ciliophoran and copepod) sequences. Gut contents also contained cryptophyte and ciliophoran genera and a few other taxa. Dinoflagellates (family Gymnodiniaceae) may be an important food source and these phytoplankton were predominant in gut contents and POM as evidenced by DNA analysis and phytoplankton cell counting. The compositions of the gut contents were not specific to the species of eel larvae or the different sampling areas, and they were most similar to POM at the chlorophyll maximum in the upper part of the thermocline (mean depth: 112 m). Our results are consistent with eel larvae feeding on marine snow at a low trophic level, and feeding may frequently occur in the chlorophyll maximum in the western North Pacific.
Highlights
The Japanese eel, Anguilla japonica, is a catadromous fish species with a spawning area at the West Mariana Ridge in the western North Pacific[1,2,3,4]
In the western North Pacific, high proportions of hydrozoans, copepods, coccidian parasites, tunicates, and fungi were detected by Next-generation sequencing (NGS) analysis of gut contents from leptocephali belonging to five Anguilliform families, including the Japanese eel, in a study designed to evaluate the level of contamination from the external surface of the larval intestines[27]
This study provides a new insight into the food sources and the feeding ecology of eel larvae in the oligotrophic tropical–subtropical western North Pacific Ocean
Summary
The Japanese eel, Anguilla japonica, is a catadromous fish species with a spawning area at the West Mariana Ridge in the western North Pacific[1,2,3,4]. The eel larvae exhibit a peculiar transparent leaf-like body form and are called leptocephali[5] Leptocephali drift from their spawning area via the North Equatorial Current, inhabit the Kuroshio to a period of 4–6 months, and are transported to the coast of Northeast Asia[6]. In the western North Pacific, high proportions of hydrozoans, copepods, coccidian parasites, tunicates, and fungi were detected by NGS analysis of gut contents from leptocephali belonging to five Anguilliform families, including the Japanese eel, in a study designed to evaluate the level of contamination from the external surface of the larval intestines[27]. Previous NGS studies in the Atlantic and Pacific oceans showed abundant hydrozoan sequences and included relatively similar eukaryotic compositions in the leptocephali gut contents
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