Photobacteriosis appeared for the first time in the Mediterranean area in 1990 causing heavy losses in fish-farms and affecting also the open sea. It affects several fish species, the aetiological agent is Photobacterium damselae subsp. piscicida. The disease is influenced by climatic changes and depends from the age of fish. The bacterium may survive in water and sediment for one month and can entry in a viable but nonculturable (VBNC) state and moreover may be transmitted to fish through water using the skin as a portal to entry. The potential exchange of pathogens between farmed and wild fish is already object of debate. Great efforts are necessary to better understand the dynamics of the disease and monitoring plans and facilities management.