A study of the reproductive cycle of the Manila clam, Ruditapes philippinarum, was undertaken at two sites in the northwest of Ireland from February 2003 to May 2004. Histological evidence showed that gametogenesis began in February and most gametes were ripe by May. Spawning began in May and continued until September. Gametes, which were ripe in October and November, were resorbed. Minimum and maximum condition indices were attained in February 2003 and June 2003, respectively, and decreased from June to September, signifying the spawning period. Vesicular cells were evident in the later gonadal stages in males. From December to March, most individuals were either spent or in a gonadal resting period. One hermaphrodite was observed. (c) 2005 Elsevier B.V. All rights reserved.