Trophic interaction, niche overlap, and species-specific feeding responses of juvenile pleuronectid flatfishes after emigration from nursery grounds in Suo-Nada, western Seto Inland Sea, Japan

Understanding the trophic interactions, niche overlap, and species-specific responses of emigrating pleuronectid juveniles provide insights into interspecific competition in shared habitats. The diet information of commercially important flatfishes in shallow nursery grounds has been well-studied in Suo-Nada, western Seto Inland Sea, Japan, whereas such information after emigration from the habitat is limited. This study aimed to reveal feeding relationships between three pleuronectid flatfishes – Pseudopleuronectes yokohamae, Platichthys bicoloratus , and Pleuronichthys lighti – and to assess seasonal changes in their feeding activity and somatic condition after emigration. As P. yokohamae and P. bicoloratus occurred in shallow nursery grounds from February to April, the post-nursery individuals were collected in the fishing ground by bottom trawl fisheries from May to August 2023. Diet composition showed that P. bicoloratus consistently consumed polychaetes, whereas P. lighti and P. yokohamae showed dietary shifts from polychaetes toward gammarids and caprellids with observed high dietary similarity between the three species. Regardless of the dietary overlap, stomach fullness decreased with the season progressed for P. yokohamae and P. bicoloratus , whereas P. lighti having a stable progression indicating different responses among the three species. Overall, feeding activity declined as the season progressed, although P. yokohamae showed pronounced mid-season increase in June before the feeding activity decreased sharply in July. These results indicate that the three pleuronectid species continue feeding after emigration from the shallow nursery grounds, but the seasonal changes in their feeding activity vary, reflecting species-specific responses to the season progression. • Seasonal shifts in feeding intensity were evident among three juvenile flatfishes. • Pseudopleuronectes yokohamae showed reduced feeding under higher temperatures. • Polychaetes dominated diets across species, indicating shared trophic niches. • Findings highlight the role of benthic prey dynamics in coastal flatfish nurseries.