Ontogenetic dietary shift of Japanese sea bass during larva-juvenile transition in Ariake Bay

Abstract

Japanese sea bass Lateolabrax japonicus larvae and juveniles were collected from Ariake Bay in order to study changes in larval diets with increasing size and changing ontogeny. Larvae of 11 to 15 mm standard length (SL) (mainly postflexion) fed on small prey such as copepod nauplii, copepodites, adult Oithona davisae and other cyclopoids; no empty guts were recorded. Metamorphosing larvae (16 to 17 mm SL) consumed prey of intermediate (Paracalanus parvus) and larger (Acartia omorii, Sinocalanus sinensis, Tortanus derjugini, Calanus sinicus, Pseudodiaptomus marinus) sizes. The highest proportion of empty guts (42 %) was recorded at this stage. The frequency of empty guts decreased steadily with the establishment of foraging on larger prey. The contribution of larger prey to the diet increased with fish size, and an exclusive large prey diet was achieved at 24.0 mm SL after which the proportion of empty guts was minimal. We conclude that a critical period in Japanese sea bass may occur at metamorphosis during larva-juvenile transition, which is associated with an ontogenetic dietary shift from smaller to larger prey.