Update on emerging abalone diseases and techniques for health assessment

This article presents a review of new diseases and additional information on known pathogens of abalone that were encountered in the last few years as a result of increasing efforts towards the culture of abalone around the world and concurrent investigations into abalone health. A novel haplosporidian was associated with high mortalities (82.5-90%) of cultured juvenile paua (Haliotis iris) in New Zealand. Disease outbreaks among cultured abalone in Tasmania, Australia were associated with two species of Vibrio (V. harveyi and V. splendidus I) and a Flavobacterium-like bacterium with stress factors precipitating the diseases in most cases. The agent of withering syndrome responsible for mass mortalities of black abalone (H. cracherodii) in southern California was identified as the Rickettsiales-like prokaryote "Candidatus xenohaliotis californiensis. The exotic sabellid polychaete that seriously impacted abalone culture in California was named Terebrasabella heterouncinata and experimentally found to reproduce at low temperatures but with a significantly temperature-dependant generation time (a developmental cycle of 298 days at 11.2 degree C in comparison to 165 days at 15.6 degree C). To assess the health of cultured abalone, histologic examinations are essential. For histology, tissue samples (less than 1 cm thick) should be fixed in Davidson's solution or 10% formalin in seawater such that there is at least 10 parts fixative to 1 part tissue. Histopathology will not only indicate the presence of infectious agents but can be useful for monitoring the suitability of the diet and aquaculture environment. These assessments will benefit abalone aquaculture and provide assurance that only healthy animals are used in stock rehabilitation programs.