- Pathogen (an organism capable of causing disease such as viruses, bacteria, fungi, parasites)
Adverse environmental conditions such as low dissolved oxygen, high levels of ammonia interacting with the host can lead to non-infectious diseases. There are some pathogens that can cause diseases to occur without the host being exposed to environment stress. These types of pathogens are obligate pathogens.
Obligate pathogens must infect a host in order to survive. The majority of pathogens that cause the most significant economic impact and pose the greatest threat to aquaculture are caused by obligate pathogens. Crayfish plague is an example of an obligate pathogen caused by a fungal disease that is capable of causing disease even in optimum environmental conditions. Read more about Crayfish plague here.
Exotic diseases are diseases caused by a pathogen that does not normally reside in a particular area and/or the population of concern has no previous experience with it. Introduction of an exotic disease can lead to epizootic outbreak (i.e. affecting a large number of animals within a geographical location) because the host has no previous experience with the pathogen so it’s immune system doesn’t have the ability to handle the disease.
The herpesvirus which caused pilchard deaths in 1995 and 1998 from Carnavon, Western Australia to Noosa Heads, Queensland is an example of the devastating impact exotic diseases. In 1998 this disease wiped out 70 % of West Australian wild pilchard stocks.
In Australia, each State and Territory has it’s own list of ‘notifiable’ animal diseases that contain diseases of either national or State/Territory concern. If you suspect your stock is infected with a notifiable disease you are legally required to immediately notify their relevant state or territory animal health authority. Notifiable disease list for Western Australia can be downloaded here!
The Role of Stress in Disease
Most diseases in aquaculture aren’t cause by obligate pathogens or exotic disease but by an interaction between the host, pathogen and the environment. Environmental stress decreases the host’s resistance to disease and increases the host’s susceptibility to pathogens that wouldn’t normal cause problems.
Reducing stress is the key in preventing most disease outbreaks in aquaculture. Read this article on the role of stress in fish disease and leave a comment to answer the following questions:
- What impact does stress have on fish?
- How do fish cope with stress?
- How can you prevent stress in fish?