Food habits of fishes in salt marsh estuaries in the western Seto Inland Sea, Japan.

Analyses of feeding patterns of fish assemblages, common approaches for understanding their habitat use and habitat dependence, have been conducted infrequently in Japanese estuarine salt marshes. The present study, based on gut content analyses, revealed the food habits of fishes occurring in salt marsh estuaries in high- and low-salinity rivers with different sediment conditions (sandy mud and muddy bottoms) in the western Seto Inland Sea, Japan. Ontogenetic changes in food preference were recognized in six species (Lateolabrax japonicus, Acanthogobius flavimanus, Glossogobius olivaceus, Platycephalus sp. 2, Acanthopagrus latus and Gymnogobius breunigii) out of 22 species examined, small individuals generally feeding on calanoid and harpacticoid copepods, and terrestrial and aquatic insects, but subsequently switching to other larger prey items (e.g., crabs, shrimps, and fishes) with growth. A cluster analysis based on dietary overlaps showed that the fish assemblages of the two salt marshes comprised nine trophic groups (zooplankton, small crustacean, large crustacean, polychaete, mollusk, fish, insect, detritus, and plant feeders), large crustacean feeders being the most abundant, followed by fish feeders, compared with polychaete and mollusk feeders, represented by only two and one species, respectively. The most important food items for the overall assemblage comprised shrimps, fishes and detritus, represented by high gut volumes in all fishes and high consumption frequencies. Furthermore, the trophic structures of fish assemblages and important food items varied between the rivers, polychaete and insect feeders being more abundant, with increasing the consumption of their main food items in the low-salinity and muddy river. Some fishes also showed remarkably different diets between adjacent rivers, highlighting small spatial scale variations in food-use patterns of fishes at the community and species levels in salt marsh estuaries. [ABSTRACT FROM AUTHOR]