Life cycle of Ceratothoa oestroides, a cymothoid isopod parasite from sea bass Dicentrarchus labrax and sea bream Sparus aurata.

Ceratothoa oestroides (Risso, 1826) (Isopoda: Cymothoida) is a protandric hermaphrodite parasite on a wide range of wild fish species. In recent years it has become a threat to cage-reared fish facilities, where high fish density provides optimal conditions for transmission. Its impact on fish health and economical gain is significant, varying from growth retardation and decreased immunocompetency to direct loss due to mass mortalities of juvenile fishes. Because of the sheltered location of the parasite in the buccal cavity of fishes, chemotherapeutics are ineffective. An understanding of the C. oestroides life cycle and its behavioral mechanisms could prove constructive tools for the prevention and control of infection. This study describes the reproductive cycle of C. oestroides experimentally induced in different fish hosts and temperature regimes. Sea bream larvae Sparus aurata and 1 yr annular sea bream Diplodus annularis were chosen as experimental models, and were held at 22 and 19.5 degrees C, respectively. The reproductive cycle of S. aurata was not completed within 4 mo (at which point the last larva died of severe anemia and respiratory distress), while that of the annular sea bream was completed successfully after 1 mo.