Comparison of Ectoparasite Pathology on Gills of Yellowfin Bream, Acanthopagrus-Australis (Gunther) (Pisces, Sparidae) - a Surface-Area Approach

Abstract

The number of gill filaments, length of gill filament and corresponding surface area affected by individual adults of Haliotrerna spariensis (Monogenea) and Ergasilus sp. and individual adults, subadults and larvae of Alella macrotrachelus (Copepoda) are examined in a large size range of the host, Acanthopagrus australis. The effects of these parasites are analysed as proportions of total filament length and total gill surface area. The parasites arranged in order of increasing number of filaments affected are: Ergasilus sp., larval A. macrotrachelus, H. spariensis, subadult A. macrotrachelus and adult A. macrotrachelus. For Ergasilus sp., H. spariensis and larval A. macrotrachelus, the length of filament affected was constant irrespective of host size; adult A. macrotrachelus affect greater lengths of filament in smaller fish, but subadult stages affect greater lengths in larger fish. Possible reasons for this are discussed. The relative pathogenicity is reduced when filament length is converted to surface area. This reduction is greater in smaller fish because they have a smaller surface area per unit length of filament than larger fish.