The recent reduction of catches of common shellfish in southern Spain has pointed out an overexploitation of these resources. For this reason, new shellfish resources have been investigated—among them, the venerid Venus nux Gmelin, 1791. To provide information to managers for a better regulation of this new fishery, we studied the reproductive cycle in the Atlantic (Huelva) and Mediterranean littoral (Malaga) of southern Spain from June 1999 to May 2000 using histology and changes in flesh dry weight. Histological examination of the gonads showed a long and asynchronous reproductive period. Spawning occurred throughout the year in both populations. Two different spawning peaks were observed: April/May for the Mediterranean population and June/July for the Atlantic one. These peaks correspond to the highest percentage of population in spawning stage, together with the greatest loss of tissue weight. During the annual reproductive cycle, new activation of the gonads from postactive stages occurred without passing through a resting period in both populations. The absence of a resting period during the reproductive cycle could be related to mild seawater temperatures (12–16°C) and high levels of chlorophyll a (2.4–4µg/L). Considering these data, we propose that if this fishery continues, and taking into account the low recruitment rate and the monocohort structure of the populations, a closed season from June to July for the Atlantic population and from April to May for the Mediterranean one should be considered for management of this new resource.