Black porgy, Acanthopagrus schlegelii (Family: Sparidae), is a commercially important fish in Japan. This species is known as a major predator of the short-neck clam Ruditapes philippinarum in tidal flats. Seasonal occurrence of large fishes such as the porgy was investigated from February 2003 to January 2004 at the Maegata tidal flat, which has the largest catch of short-neck clam in Hiroshima Bay, western Seto Inland Sea. As a result, 73 individuals from nine species were collected by monthly gill net sampling. A. schlegelii, 23.6-48.5 cm total length was the dominant species and accounted for 79% of the total individuals. The catch per unit effort (CPUE: number of fish caught/300 m of netting) of the porgy was 0–18.8. The CPUE rapidly increased in late June. In late July, it reached 18.8, the highest annual value, after which the CPUE maintained high values during late August and late September. From late November values were low (0-3.0) again. These results indicate that large-sized A. schlegelii occur seasonally in the tidal flats from late June to late October.