POPULATION-DYNAMICS OF THE METACERCARIAL STAGE OF THE BUCEPHALID TREMATODE, LABRATREMA-MINIMUS (STOSSICH, 1887) FROM SALSES-LEUCATE LAGOON (FRANCE) DURING THE CERCARIAL SHEDDING PERIOD

The population dynamics of Labratrema minimus (Stossich, 1887) metacer cariae (Trematoda, Bucephalidae) were studied in its second intermedia te fish host Atherina boyeri from Salses-Leucate lagoon (Northwest Med iterranean Sea, South of France), during the cercarial shedding period . The infection parameters (prevalence and mean abundance of infection ) showed the high susceptibility of silversides (juveniles and adults) to infection. The observed variation in the mean abundance of infecti on with respect to time and host size was explained by (i) the suscept ibility of A. boyeri to multiple successive infections (increase in ab undance of infection with host length and raising of parasite burden u ntil August) and (ii) the loss, probably by more rapid death, of heavi ly infected silversides from each host size group (decrease in abundan ce of infection in September within each host size group, stability of the parasite burden within the older class of hosts over the whole pe riod, premature decrease in the condition factor in August). Finally, it was deduced that the infection pattern observed over the May-Septem ber period was a dynamic process controlled by: availability of infect ive cercariae, influx of newborn silversides free of metacercariae unt il September, high susceptibility of juvenile and adult A. boyeri to i nfection, metacercarial loss and probably by parasite-induced host mor tality.