Fishes were sampled using an overnight light trap at Ronden and Teratsu in Lake
Shinji and Eshima in Nakaumi Lagoon from March through June 2009, with an aim to reveal
the spatial and temporal variation of larval and juvenile fish fauna in these lakes. A total of 7416 individuals of 6 species, 52 individuals of 6 species and 1466 individuals of 10 species were collected in the respective sampling sites. In Lake Shinji, Gymnogobius taranetzi (49.6% of total individuals) and Salangichthys microdon (48.6%) were almost entirely dominated at Ronden, and Gymnogobius taranetzi (40.4%), Hypomeus nipponensis (26.9%) and Salangichthys microdon (21.2%) were also dominated at Teratsu. At Eshima in Nakaumi Lagoon, Chaenogobius spp. (67.7%), Tridentiger spp. (16.6%), Acanthogobius flavimanus (7.3%) and Gymnogobius breunigii (5.7%) were determined to be the dominant species. Both larvae and juveniles of “amphidromous species” and“ estuarine species” mainly occurred in Lake Shinji, while those
of“ estuarine species” and“ marine species” occurred in Nakaumi Lagoon. Results of this study indicate that the difference of larval and juvenile fish fauna reflect the diverse reproductive mechanisms of amphidromous, estuarine and marine fishes in Lake Shinji and adjacent Nakaumi Lagoon along the estuarine salinity gradient between these lakes.