Infection of sardine eggs by the protistan endoparasite Ichthyodinium chabelardi off Portugal

In 1997 and 1999 around 30% of the stations off Portugal sampled for sardin e eggs Sardina pilchardus included eggs infected with Ichthyodinium chabela rdi. A randomization test on the mean nearest neighbour distances of parasi tized stations did not reveal evidence of significant spatial clustering. T he mean prevalence of infection was c. 0.05 for both years, but the probabi lity of parasite detection increased considerably with egg age, Eggs in the ir first day of development (before the embryo is formed) were not parasiti zed: most parasitized eggs were in the cohorts close to hatching. Although the reasons for age-dependent detection are unknown. if all parasitized egg s of the cohort ready to hatch were to die, infection by Ichthyodinium chab elardi would lead to mortality rates similar to those reported for the aver age daily mortality of sardine eggs and early larvae. (C) 2000 The Fisherie s Society of the British Isles.