The occurrence, distribution and pathology associated with gnathiid isopod larvae infecting the epaulette shark, Hemiscyllium ocellatum

Abstract

Gnathiid isopod praniza larvae were found to infect the epaulette shark Hemiscyllium ocellatum. All sharks carried larvae on their external body surface, with the preferred attachment site in both sexes around the cloaca ( P<0.05). The claspers were the second site of preference in male sharks. Within the buccal and branchial cavities, about 16% of larvae were attached to the roof and floor of the mouth and 84% attached to the gills. A significant positive correlation existed between larval number and fish size. Histological examination showed that larval attachment in the buccal cavity elicited variable responses, the most severe being a loss of epithelium and compression of underlying tissue. No host cellular response or tissue proliferation was observed. Praniza attached preferentially to the efferent side of gill filaments (relative to blood flow), and caused loss of epithelium, compression of tissue, and a small amount of connective tissue proliferation. Attachment to the gill septum or to the afferent side of the gill filament caused lamellar disruption, a cellular inflammatory response, and connective tissue proliferation. Scanning electron microscopy showed little obvious praniza-induced gill damage, other than localised tissue distortion to form pockets around larvae attached between filaments. The results suggest that praniza larvae do not cause sufficient tissue damage to adversely affect the health of this shark species.