GUT OF GOATFISHES, A HETEROGENEOUS BIOTOPE FOR INTESTINAL MESOPARASITES - VARIATIONS IN PYLORIC CECA NUMBER AND GROWTH-MODELS OF COLONIZABLE DIGESTIVE SURFACE-AREA

Fish organs constitute biotopes for various parasites. In the case of gills or digestive tracts, hosts of different ages and sizes lead to a heterogeneity in these biotopes at the fish population level. The dig estive tracts of goatfishes Mullus surmuletus and M. barbatus harbour several species of helminths that colonize the pyloric caeca and intes tine. The structural heterogeneity of this biotope is analysed by stud y of variations in caeca number and colonizable surface area. Caeca nu mber varies between host species and among individuals of the same pop ulation. Colonizable intestinal surface area also varies between goatf ish species and increases with fish size, but differently according to the intestinal parts considered. These variations were studied, using image-processing techniques, and analysed quantitatively. Theoretical growth models are proposed and some consequences for parasite ecology discussed. (C) 1998 The Fisheries Society of the British Isles.