Microhabitat distribution and coexistence of Microcotylidae (Monogenea) on the gills of the striped mullet Mugil cephalus: chance or competition?

The two monogenean species Metamicrocotyla cephalus and Microcotyle mugilis have specific microhabitats on the gills of Mugil cephalus on which they may or may not coexist. M. cephalus is found in sector 1 of the posterior hemibranch of arch I. M. mugilis is found on the filaments of sector 5 of the posterior hemibranch of arch I. The coexistence of these two monogenean species on the same fish does not induce a change in their respective distribution, except for a marked preference of M. cephalus for the left side and of M. mugilis for the right. This 15-month-long study shows that when the two species of monogeneans coexist the infection prevalence and intensity are higher than in cases of monospecific infection. The specific character of the microhabitat, the apparent absence of interspecific competition, and the existence of positive species interactions are discussed.