Food habits of three species of juvenile rockfish co-occurring in Hiroshima Bay, the Seto Inland Sea, Japan

Abstract

The diets of three juvenile rockfish species (Sebastes inermis, S. ventricosus, and S. cheni) are poorly understood because they had been treated as a single species until recently. To address the lack of data on their diets, we examined the stomach contents of juvenile rockfish collected from both macroalgal (Sargassum macrocarpum) beds and docks in Hiroshima Bay, the Seto Inland Sea, and analyzed their dietary differences based on the location (five islands), habitat type (macroalgal bed and dock), and species. We found that these juveniles primarily consumed both epifaunal and planktonic small crustaceans, especially amphipods, calanoids, and ostracods. Moreover, their diet composition differed significantly based on the location and habitat type, but not based on the species. These results indicate that these three species are opportunistic feeders and may compete for food. However, the difference in habitat types predominated by S. inermis and S. ventricosus suggests that interspecific competition for food is not strong between both species. Furthermore, the docks may function as feeding grounds for juvenile rockfish, as well as the macroalgal beds, because their stomach fullness indices did not differ significantly between the two habitats.