GILL FILAMENTS OF LIZA-RAMADA, A BIOTOPE FOR ECTOPARASITES - SURFACE-AREA ACQUISITION USING IMAGE-ANALYSIS AND GROWTH-MODELS

Ecology of plant or animal communities requires knowledge of the bioto pe structure of these organisms. In the case of parasitic communities, the organs of a host constitute heterogeneous biotopes. Fish gills ar e an example of this, but their heterogeneity is not often considered. The gills of the muller Liza ramada are such a biotope for several ec toparasites. Parasite density is an important Factor in the study of f ish-parasite interactions, but cannot be determined if the colonized s urface area of the gills is not known. The number of primary filaments , and therefore the surface area potentially colonized, is subject to variation with age. Assessment of the colonizable area raises specific problems of estimation. A new method taking into account surface area s of primary filaments and using image processing techniques is propos ed. Models related to the increase of filament number and colonizable gill area as functions of the fish fork length are proposed. The incre ase of primary lamellae number with fish length can be fitted by an ex ponential-type model and the accompanying increase in size of the colo nizable gill area by a polynomial-type model. (C) 1996 The Fisheries S ociety of the British Isles