This paper aims to assess the diel feeding pattern and seasonal variation in the daily ration of immature and mature marbled flounder (Pseudopleuronectes yokohamae ). A day‐night collection by bottom trawls was conducted in Sendai Bay in July 2014. Marbled flounder (131–493 mm total length; Number of collected individuals = 1830, Number of analyzed individuals = 497) fed mainly on polychaetes during the day. At night, stomach content weight decreased with time, but the weight and proportion of bivalve siphons were consistently higher at night than during the day, suggesting nocturnal feeding by the flounder on bivalve siphons. Daily ration was greater in females (<300 mm: 2.6%–3.2% body weight; ≥300 mm: 1.5%–2.5%) than in males (<300 mm: 1.7%–2.6%; ≥300 mm: 1.3%–1.9%). Seasonal surveys were also carried out, and the greater ration in females than males were consistent throughout the year, suggesting that greater growth in females than males attributes to the greater food intake of females. The ration was highest in June, especially for large individuals, although water temperature in June was lower than that in September. These results indicate that the amount of food intake is related to the annual life cycle of the marbled flounder.

This work was partly supported by the Stock Assessment Program of Fisheries Agency and Fisheries Research and Education Agency of Japan and the program “Project on Clarifying the Impact of Nuclear Substances” of the Fisheries Agency of Japan.