Pathogens and probionts of ornate spiny lobster ('Panulirus ornatus') phyllosoma

Abstract

Wild capture production of economically important spiny lobster (Palinuridae) fisheries has stagnated or declined in recent decades, and with an array of global climatic, economic and demographic challenges limiting the opportunities to enhance production, alternative supplies need to be sourced through aquaculture. Among the prospective aquacultures species is the ornate spiny lobster ('Panulirus ornatus'), however sustainable farming will only be met through refining larviculture technologies and the development of disease management strategies to counter epizootics. This study investigated bacterial pathogens causing epizootics in 'P. ornatus' larviculture and examined a potential biocontrol strategy using probiotics. The type strain of 'V. owensii' (DY05) was validated by Koch's postulates as the aetiological agent of disease causing rapid and reproducible mortalities of early stage 'P. ornatus' phyllosoma larvae. The pathogenicity and infection cycle of 'V. owensii' DY05 were investigated using in vivo experimental infection models and a V. owensii DY05 transconjugant expressing a fluorescent protein (FP), which showed Artemia-vectored challenge to be a crucial determinant in the infection process. Soon after ingestion by phyllosomas (6 h), fluorescently labelled cells were monodispersed in the proventriculum (foregut) and hepatopancreas (midgut gland), which preceded mass proliferation in the hepatopancreas and evacuation of planktonic cells into the ambient environment. Continued bacterial proliferation lead to systemic infection and the sustained presence of cells in phyllosoma tissues post mortem. Clinical pathologies included hepatopancreatic epithelial cell necrosis, and in vitro enzyme assays identified proteases, phospholipases, and haemolysins as potential virulence factors. The observations indicated 'V. owensii' DY05 is a specialist enteropathogen of 'P. ornatus' phyllosomas, using vector-mediated transmission and release from host-associations to a planktonic existence to perpetuate transfer.