About epizootic ulcerative syndrome
Epizootic ulcerative syndrome (EUS) is caused by a water mould (Aphanomyces invadans) that occurs in fresh water and estuaries at water temperatures ranging between 10°C and 33°C but has been shown to grow better in warmer waters (20°C to 33°C). A. invadans attaches to damaged skin of fish, causing ulcers and killing the tissue in the infected area.
EUS can be associated with large rainfall events and has been shown to have a low salinity tolerance.
Global distribution of EUS
Data sourced (with updates or corrections as necessary) from the CABI Compendium
Why this is a problem for New Zealand
EUS can infect many different types of fish both in the wild and in aquaculture. It kills most of the fish it infects and can spread through water. Establishment of EUS in New Zealand could have economic, environmental, and sociocultural impacts. It could affect native fish populations and impact commercial and recreational fishing.
How it could get here
The Ministry for Primary Industries (MPI) has strict measures in place to limit the chances of exotic aquatic diseases like EUS entering New Zealand through infected fish, aquatic animal products, or contaminated gear.
Importing into NZ: how it works
How to identify infected fish
Disease in fish is difficult to diagnose. Signs of illness can have many causes, and the first indication may be unusual fish behaviour or mass mortalities, especially in wild populations. The only accurate way to confirm a diagnosis is through laboratory testing. Fish infected with EUS may exhibit none, one, or multiple, of the following signs:
- single or mass mortality
- skin ulcers, or red spots
- unusual behaviour.
As with most fish diseases, these signs are not specific to EUS and may be caused by other conditions. Laboratory testing is required for confirmation.
New Zealand guide to aquatic disease signs [PDF, 1.6 MB]
If you think you've found an infected fish
- Take a photo or a video.
- Note the location (GPS coordinates where possible) and any landmarks (if found in the wild).
- Collect a sample (if it is safe to do so) and keep chilled (do not freeze).
- Call the MPI pest and disease hotline 0800 809 966 or fill in our online form
Tips for finding and identifying pests and diseases
Related information
WOAH health standards for Aphanomyces invadans [PDF, 285 KB]
Note: This information is a summary of this disease's potential impacts on New Zealand.