Occurrence of Perkinsus olseni and other parasites in New Zealand Greenshell™ mussels (Perna canaliculus)

Abstract text

The New Zealand Greenshell™ mussel (Perna canaliculus) is endemic to New Zealand and is the top shellfish export product. However, the growth of this industry is being adversely affected by potential disease outbreaks. To assess these health threats, a detailed histopathological examination of a targeted survey/sampling of farmed mussels (P. canaliculus) was undertaken. Histological sections followed by confirmatory in situ hybridization (ISH) resulted in the identification of Perkinsus olseni (56% prevalence). Apicomplexan parasite X (APX) (78%), copepods (Pseudomyicola spinosus or Lichomolgus uncus) (1%), Microsporidium rapuae (1%), intracellular microcolonies of bacteria (IMCs) (2%) and, bacilli and cocci bacteria (4%) were also identified across organs. There was a significant association between P. olseni and APX infection in mussels. The abundance of P. olseni and APX in P. canaliculus was evaluated semi-quantitatively using two separate modified grading scales, which are suitable to assess P. olseni and APX infection of the histological section. Immunological tissue responses (haemocytosis and ceroid material) were also evaluated semi-quantitatively and were significantly associated with P. olseni and APX. The pathologies of digestive tubules and gills were observed in this study and P. olseni infection is related to digestive tubule deterioration (large lumen, with a thin epithelial wall). A significant association between the presence of parasites and the health conditions (healthy and unhealthy) of mussels were observed. Therefore, the findings in this study provide information regarding the infections of potential parasites and health conditions in New Zealand Greenshell™ mussels (P. canaliculus).

Keywords: Apicomplexan X; Ceroid material; Haemocytosis; In situ–hybridization; Perkinsus olseni; Histology.