Microhabitats, attachment of eggs and histopathology by the monogenean Allomurraytrema robustum on Acanthopagrus australis (Pisces: Sparidae)

Abstract

Allomurraytrema robustum occurs normally in low numbers on the jaws, gill arch or upper palate; juveniles also occur on the lateral margins of the gill filaments. At high levels of infection the parasite occurs in large groups (> 30 worms) on the jaws and gill arches, and extends onto the lateral margins of the gill filaments. Large numbers of eggs become entangled among these groups of parasites. Ciliated oncomiracidia emerge from the eggs. The parasite attaches to the surface of epithelia by small hamuli and marginal haptoral hooklets, but an adhesive secretion may be involved as well. The parasite causes little damage when attached to thick epithelia, but on the surface of the gill filaments there is erosion and degeneration of the epithelium beneath and adjacent to the haptor. Infiltrating leucocytes enter the dermis, epidermis and the host-parasite interface. Intact infiltrating cell occur in the intestinal caeca of the parasite.