Comparative pathology of some monogenean and copepod ectoparasites on the gills of Acanthopagrus australis (family Sparidae)

The monogenean Haliotrema spariensis was associated with several foci of hyperplastic epithelium and varying amounts of cellular infiltration resulting from attachment by hamuli penetrating the lamellar blood vessels and, presumably, from feeding. Lamellodiscus major was associated with fewer but larger foci containing more extensive infiltration, suggesting a more sessile habit. The copepod Dermoergasilus acanthopagri encircled the filament with its second antenna, occluded arteries and compressed the epithelium, resulting in hyperplasia, oedema and infiltration. Ergasilus lizae inserted its second antennae into the epithelium and subepithelial region and was associated with a localized proliferative response occasionally fusing adjacent filaments. The large copepod Lernanthropus atrox caused tissue disruption, hyperplasia, haemorrhage, oedema and infiltration. Hyperplastic epithelial cells had a rounded nucleus containing variable amounts of heterochromatin, dilated organelles, deposits of glycogen‐like particles, cyoplasmic vesicles and vacuoles. Oedematous epithelial cells were less altered. Degenerating chloride cells were present in both oedematous and proliferated epithelia