One of the most important negative impacts of fish culture is the fact that farmed fish are more susceptible to disease agents than their wild counterparts due to the artificial conditions posed by intensive rearing. However, the natural sources of fishes are becoming poorer because of pollution and unmanaged fishing of many immature fish.
Adverse environmental situations may acutely or chronically stress fish health, altering some of their biochemical parameters and suppressing their innate and adaptive immune responses. These drastic impacts are manifested in the high fish mortality from acute infections and the lowered growth rate and food conversion in the chronically diseased ones with the end result of decreased fish production outcome. Nowadays, the main objective of fish pathologists is not only directed to overcome the infectious outbreaks appear, but also how to prevent the spread of diseases in the different fish culture systems in order to produce a safe and cheap good quality animal protein for human consumers. To fulfill this important issue, microbial epidemiological studies for the different available fresh water and marine water environments suspected to be sites for fish production are urgently required.