Safe, simple, and effective biocontrol of Yersinia ruckeri!

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CUSTUS®YRS is safe, simple and effective. Yersiniosis, or enteric red mouth disease (ERM) as it is also called, is an infectious disease caused by the bacteria Yersinia ruckeri (Y. ruckeri). CUSTUS®YRS contains naturally occurring bacteriophages that specifically infect and kill Y. ruckeri.

Using CUSTUS®YRS reduces the infective pressure from Y. ruckeri in water in situations in which the fish are particularly vulnerable to catch an infection or situations likely to cause an outbreak, such as transport, vaccination, sorting or delicing.


Yersiniosis – a substantial challenge to fish farms.

Yersiniosis in salmon is caused by the bacteria Yersinia ruckeri (Y. ruckeri). Globally, multiple serotypes of Y. ruckeri exist, but in Norway, outbreaks of yersiniosis is primarily associated with serotype O1. Initially detected in Norway in 1985. Yersiniosis has since then occurred in atlantic salmon (Salmo salar) in fish farms along the entire Norwegian coast. However, the rate of occurrence the last decade has been higher along the Mid-and Northern coast of Norway. Previously, yersiniosis was presumed to be a fresh water problem, occurring primarily in the hatcheries/pre smolt phase. This perspective has changed in the recent decade, as the number of reports and the severity of yersiniosis outbreaks at sea has increased. This is shown by the Veterinary Institutes diagnostic service results, which are summarized in their yearly fish-health report (Figure 1) (Citation: Fiskehelserapporten 2017).

Yersiniosis is now reported both in fresh water and sea water, where it causes significant losses due to increased morbidity and mortality. In fresh water, the disease can cause substantial loss of small fry and cause repeated outbreaks. At sea, the majority of outbreaks cause mortalities after the initial transfer to sea pens or after handling, and an increased number of reports of yersiniosis outbreaks in larger fish post-handling has been observed. A possible link between delicing of fish and outbreaks of yersiniosis has been implied.

Figure text from the fish-health report: Distribution of Y. ruckeri detected by the Veterinary Institute since 2004. Multiple detections from the same location within the same year are only counted as one. This only includes a partial description as public communication of yersiniosis in fish is NOT mandatory in Norway.

CUSTUS®YRS – A new tool to reduce the infection pressure from Yersinia ruckeri.

Understanding how pathogenic bacteria spread and cause disease in aquaculture is important. Infection is not as simple as a yes or a no. A negative result could just mean there wasn’t enough bacteria present in the small sample volume analyzed. Re-analysis of a larger volume of water could still yield a positive result. In the field, our analyses often reveal the presence of Yersinia in surprisingly high concentrations, even if there isn’t an outbreak.

In farms or in their natural environment, the fish are constantly exposed to infection pressure from pathogenic organisms, but are mostly healthy, due to their well-functioning protective barriers and immune system. The fish farmers work hard to minimize the infection pressure and improve fish health and welfare through a number of measures (e.g. good hygiene and water quality, vaccination, high quality feed etc.). However, managing a fish farm also means that a number of operations like sorting, vaccination and transportation must be performed. These operations are stressful to the fish. As such, its resistance to infection is significantly reduced and the risk of an outbreak occurring is increased.

There is a link between performing stressful handling operations and outbreaks of yersiniosis. Use CUSTUS®YRS to control the infection pressure from Y. ruckeri and minimize the risk of an outbreak.

CUSTUS®YRS is safe, simple, and effective!

CUSTUS®YRS are shipped in bottles and is easily added to the water. The bottles contain mostly water, a pH-buffer, stabilizing salts and a minimum of five hundred thousand billion bacteriophages per liter (5×1011 per liter). When used as intended and at the recommended dose the bacteriophages in CUSTUS®YRS infect and kill Y. ruckeri, without affecting the surrounding organisms in the environment, including the commensal microflora or the fish, water, or the biofilter!

CUSTUS®YRS is safe and well-documented through safety studies performed at ILAB in Bergen, at Veso Vikan (GLP) and in field trials. No mortality, no morbidity, and no other side-effects have been observed from using CUSTUS®YRS in salmon, not even at 2000x the recommended dose. All safety studies have been performed under the approval of the Norwegian Food Authorities (FOTS).


  • CUSTUS®YRS is safe for the fish!
  • CUSTUS®YRS is safe for humans!
  • CUSTUS®YRS is safe for the commensal microflora!
  • CUSTUS®YRS is safe for the biofilter!
  • CUSTUS®YRS is safe for the environment!


Get started with CUSTUS®YRS !

Because the bacteriophages are so specific, the first step is to confirm the presence of Y. ruckeri and characterize the isolates sensitivity to the CUSTUS-bacteriophages. If you are an operations manager, a fish health biologist, or a veterinary at a facility experiencing challenges with yersiniosis, please contact us for information about how to get your water samples analyzed, and your bacterial isolates characterized. We also offer a thorough investigation of your facility to identify potential key reservoirs for Y. ruckeri.

If you experience any other challenges with bacteria, please do not hesitate to contact us about it. We depend on your knowledge, experience, and bacterial isolates to develop new bacteriophage products for the future!