Abstract
Serranicotyle labracis (Van Beneden and Hesse, 1863) Maillard, Euzet and Silan, 1988 (synonym : Microcotyle labracis Van Beneden and Hesse, 1863) is a monogenean Polyopisthocotylea and a gill parasite of the sea bass Dicentrarchus labrax (Linné, 1758). Analysis of a western Mediterranean population of this parasite (Gulf of Lions, Languedoc, France) clarified several aspects of its biology. Its location in the gill biotope (Silan et al., 1987) was not fundamentally different from that found by Oliver (1977) and Winch (1983), but its distribution in host populations differed from that reported in the earlier studies ; its displayed a negative binomial distribution in the study zone. At a finer level of observation, the behaviour of the hosts, as a function of degree of maturity and sex, appeared to determine more than any other factor the extent of infestation by the parasite. Previous suggestions in the literature to account for these differences in population dynamics are discussed.