INTRODUCTION
Since the 1960’s, a variety of marine fish in several parts of the world have been frequently infected with a highly virulent bacterium originally called Pasteurella piscicida (thus the name Pasteurellosis). 

The disease was renamed in 1995 and is now officially called Photobacterium damsela subspecies piscicida. 

ETIOLOGY
Photobacterium damsela subsp. piscicida is a Gram-negative, pleomorphic, non-motile bacterium that grows slowly on NaCl-supplemented media. 

Serologically, the strains found all over the world are highly homogeneous and there seems to be only one serotype. However, ribotyping revealed genetic variation of different geographical isolates.