Aetiology / Introduction

Photobacterium damsela subsp. piscicida was known until recently as Pasteurella piscicida. It is a Gram-negative rod which causes a disease in fish known either as pseudotuberculosis or fish pasteurellosis.

This serious problem in Japanese yellowtail culture can result in losses on individual farms of up to 50%. The bacterium's taxonomic position as a bonafide Pasteurella has been questioned for a number of years and based on small subunit ribosomal ribonucleic acid (rRNA) sequences, whole deoxyribonucleic acid (DNA) relatedness and biochemical characterization, Gauthier et al. (1995) have reassigned the bacterium to a subspecies of P. damsela. Some fish farmers and scientists may still refer to the disease as pasteurellosis.

Epidemiology

Photobacterium damsela infections have been confirmed in the USA, Japan, Taiwan, Spain, Greece, France, Portugal and Norway. Though previously confused with the other common fish pathogens, Vibrio anguillarum and Aeromonas salmonicida subsp. salmonicida, this bacteria differs from the others as well as Pasteurella spp.

Researchers have found that isolates from several European countries, Japan and the USA are biochemically and antigenically similar, with homogeneous lipopolysacharide (LPS) electrophoretic patterns and membrane protein profiles.

Diagnosis

Photobacterium damsela causes a disease sometimes referred to as pseudotuberculosis or fish pasteurellosis. It can cause massive losses in fish populations, both cultured and in the wild.

The disease is characterized by numerous, white bacterial colonies throughout the internal viscera, especially the kidneys and spleen