Pathological changes in the gill filaments of Acanthopagrus australis (family Sparidae) associated with the post-settlement growth of a lernaeopodid copepod, Alella macrotrachelus

The extent of the histopathology associated with the attachment of post-settlement stages of the lernaeopodid copepod Alella macrotrachelus on the gills of Acanthopagrus australis was related to parasite size. Initial penetration of the attachment organ into the epithelium was associated with hyperplasia, oedema and accumulation of infiltrating cells in the immediate vicinity of the frontal filament or bulla. Adult parasites caused crypting and fusion of filaments with associated chronic inflammation. Penetration of the bulla into the connective tissue invoked fibroplasia and chondrocyte proliferation that enclosed the bulla. The bulla matured from the centre to the periphery by a condensation of the matrix into coarse fibrils. The bulla was delineated by a tri-laminar wall from the surrounding connective tissue fibrils.