We examined larval myctophid fish assemblages and their distribution patterns, based on discrete depth sampling. Samples were collected at 19 stations along a transect that crossed the subtropical-tropical waters of the western North Pacific. In total, we collected 27 189 larvae of 40 myctophid species or types, belonging to 15 genera. Three assemblages were recognized, based on their species composition: Kuroshio Axis (KuA), Kuroshio Countercurrent (KCC), and Subtropical Countercurrent-North Equatorial Current (SCC-NEC) assemblages. The distributions of these assemblages were well defined by the positions of the KuA and the Subtropical Convergence. Each species had a specific distribution depth, and none showed diel vertical migration. Larvae of the subfamily Lampanyctinae were distributed in shallower waters (0-50 m) than larvae of the subfamily Myctophinae (50-150 m). Larvae of the same species were distributed at lower depths in the SCC-NEC area than in the KCC area. This corresponded to the abundance of chlorophyll a, which would reflect abundance of prey organisms such as copepod nauplii and copepodites.

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The occurrence and density of Pacific saury Cololabis saira larvae and juveniles were examined in relation to environmental factors during the winter spawning season in the Kuroshio Current system, based on samples from extensive surveys off the Pacific coast of Japan in 2003–2012. Dense distributions of larvae and juveniles were observed in areas around and on the offshore side of the Kuroshio axis except during a large Kuroshio meander year (2005). The relationships of larval and juvenile occurrence and density given the occurrence to sea surface temperature (SST), salinity (SSS), and chlorophyll‐a concentration (CHL) were examined by generalized additive models for 10‐mm size classes up to 40 mm. In general, the optimal SST for larval and juvenile occurrence and density given the occurrence was consistently observed at 19–20°C. The patterns were more complex for SSS, but a peak in occurrence was observed at 34.75–34.80. In contrast, there were negative relationships of occurrence and density given the occurrence to CHL. These patterns tended to be consistent among different size classes, although the patterns differed for the smallest size class depending on environmental factors. Synthetically, the window for spawning and larval and juvenile occurrence and density seems to be largely determined by physical factors, in particular temperature. The environmental conditions which larvae and juveniles encounter would be maintained while they are transported. The survival success under the physically favorable but food‐poor conditions of the Kuroshio Current system could be key to their recruitment success.