Spatial distribution of ectoparasites on the gills of the mullet, Liza macrolepis: the effects of pollution.

Spatial distribution of ectoparasites on the gills of the mullet Liza macrolepis collected from two sites, the unpolluted reference site (Site I) and the heavily polluted North western arm of Visakhapatnam harbour (Site II), was analysed. Of the various ectoparasite species found on the gills of the mullet, only Ancyrocephalus vanbenedeni (Monogenea) and Dermergasilus varicoleus (Copepoda), occurred commonly at both the sites with more or less high prevalence and mean intensity. A. vanbenedeni at site I preferred gill arch 1 and posterior most and central sections, whereas at site II, it showed preference for gill arch 3, and posterior and proximal sections of the gill. D. varicoleus is highly specific in site selection. It preferred gill arch 1 and the anterior and distal parts at both the sites. Ergasilus rostralis favoured gill arch 3 and anterior and proximal sectors, a safe place providing absolute protection from the environmental pollution. It is concluded that the distribution of various ectoparasites on the gills of L. macrolepis is determined by the force of ventilation water current, the behavioral response of the parasite to the stress induced by pollution and the surface area of gill arches.