Southern Bluefin Tune (SBT) ranching operations have evolved rapidly and industry has experienced relatively few serious issues through its short history. However, some ranching operations have reported an increase in cumulative mortality and in some severe cases, up to 90% of collected mortalities present some degree of unilateral or bilateral ocular damage. Anecdotal reports of eye lesions has progressively increased since the 2015 and previous research identified sea lice of the genus Caligus spp. are potentially a differential cause of eye lesions in SBT. The copepod ectoparasite is thought to damage the eyes by feeding on the cornea epithelium of infested SBT. Lesions worsen when fish flash against the cage’s net to dislodge the itchy copepods. Partial or full vision loss is suspected to impair the capacity of the fish to compete for feed and to result, with time, in the death of affected fish.

This investment will estimate the frequency and distribution of increased mortality across the industry and describe the pathology and severity of eye lesions and estimate the frequency and distribution of these lesions across the industry. The project will also investigate potential tow-, farm-, and fish-level risk factors associated with increased mortality and eye lesion occurrence and the putative role of sealice in causing eye lesions.