Abstract:Copepod nauplii are the primary food item for early-stage marine fish larvae, but their feeding selectivity on the nauplii of different copepod species has not been well studied. This study revealed feeding selectivity in the dominant preflexion larvae of three fishes Sebastiscus marmoratus, Sebastes sp. and Ammodytes japonicus in the Seto Inland Sea, Japan, in spring and winter. Copepod nauplii and eggs numerically constituted 80-91% of the prey items in their guts. Chesson s preference index for the nauplii of various copepod species was positive for Calanus sinicus and Paracalanus parvus sensu lato, negative for Acartia omorii, and negative or neutral for Oithona similis. This result is probably attributable to the size and swimming behavior of the prey species. The preference index in A. japonicus larvae was not significantly different between the nauplii of different species, suggesting that the larvae are less selective than the other two fishes. The preference index for Calanus eggs was very high, especially in Sebastiscus marmoratus and Sebastes sp., and most of the eggs in the guts were shrunken, probably due to digestion. In terms of volume, C. sinicus nauplii and eggs in gut contents represented 36-72% of total copepod nauplii and >80% of total copepod eggs, respectively, because of high selectivity by fish larvae and their large individual volumes compared with the dominant copepods. This indicates that C. sinicus is the most important prey species for early fish larvae despite their low abundance in the environment.