New Zealand rickettsia‐like organism ( NZ ‐ RLO ) and Tenacibaculum maritimum : Distribution and phylogeny in farmed Chinook salmon ( Oncorhynchus tshawytscha )

Abstract

A total of 777 fish from three growing regions of New Zealand Chinook salmon farms comprising of five sites were tested. Quantitative PCR was used to determine the distribution of New Zealand rickettsia‐like organism and Tenacibaculum maritimum . Genetic information from these bacteria were then compared with strains reported worldwide. Using this information, suggested associations of pathogens with clinically affected fish were made. NZ ‐ RLO was detected in two of the three regions, and T. maritimum was detected in all regions. Three strains of NZ ‐ RLO were identified during this study. Based on analysis of the ITS rRNA gene, NZ ‐ RLO 1 appears to be part of an Australasian grouping sharing high similarity with the Tasmanian RLO , NZ ‐ RLO 2 was shown to be the same as an Irish strain, and NZ ‐ RLO 3 was shown be closely related to two strains from Chile. Based on multi‐locus sequence typing, the New Zealand T. maritimum was the same as Australian strains. NZ ‐ RLO s were detected more frequently in fish with skin ulcers than fish without skin ulcers. While additional research is required to investigate the pathogenicity of these organisms, this is the first time that NZ ‐ RLO s have been associated with the development of clinical infections in farmed Chinook salmon.

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