FAQ – Bacteriophage solution, CUSTUS®YRS

If you have additonal questions, feel free to contact us.

What is a bacteriophage?

Bacteriophages are viruses that exclusively kill specific bacteria. They are found in big variations and huge numbers in any environment on the planet. In food, people, water, soil, – everywhere you find bacteria you also find bacteriophages. The word “bacteriophage” means “bacteria eater”. In nature, they control the growth of bacteria by feeding on them.

Why should I use bacteriophages at my hatchery/site?

Bacteriophages kill bacteria, it will reduce the infection pressure (number of bacteria in the water) and help avoid bacterial infection in the fish. This leads to better fish welfare and production.

What infection is ACDs product CUSTUS®YRS targeting?

CUSTUS®YRS contains bacteriophages which specifically infects and kills the bacteria Yersinia ruckeri. CUSTUS®YRS is used to reduce the infection pressure of Yersinia ruckeri without affecting the rest of the microflora in the water.

Are bacteriophages dangerous?

No. They are only dangerous to the bacteria they are specialized to infect and kill.

Are there any side effects?

No. Only the targeted bacteria – in this case, only Yersinia ruckeri, is affected by the water treatment. Bacteriophages are everywhere. All living organisms as well as the environment around us are constantly being exposed to bacteriophages.

What is the mode of action? How can bacteriophages prevent Yersiniose?

Yersinia ruckeri specific bacteriophages are already present in the water in hatcheries that have problems with this bacterium, however the concentration of bacteriophages is too low for the bacteria to be positively affected by its presence. By using CUSTUS®YRS you will increase the concentration of bacteriophage, significantly increasing the likelyhood of infection and termination of the Yersinia-bacteria.

How do you add the bacteriophages to the environment around the fish?

CUSTUS®YRS is delivered as a water solution that you add directly to the production water or in the tanks.

In what parts of production should bacteriophages be used?

• In closed systems and production situations such as in hatcheries and transportation tanks.


• In recirculation systems (RAS) to control specific bacteria presence without affecting the natural microflora and biofilter.


• In conjunction with stressful situations such as handling the fish or when you know that the fish is vulnerable to a high infection pressure of Yersinia ruckeri. For example, vaccination, grading or transport.

When should I use CUSTUS®YRS?

You should use CUSTUS®YRS in conjunction with stressful operations such as vaccination and grading, and in periods where it’s important to control the infection pressure because of vulnerability for disease outbreaks.

How can this improve the situation at my hatchery?

CUSTUS®YRS help you control the infection pressure without affecting the natural microflora in the water. This is the beginning of a good circle; better water quality = reduced risk of disease outbreaks, reduced risk for destruction and fallowing, better reputation, better production.

Can bacteriophages affect the environment?

Yes, and that is the point. Bacteriophages are from nature and carry out an important role in the environment. In nature, they keep the numbers of bacteria at a level tolerable to other organisms in the environment.


By consciously adding bacteriophages to the water gives you the opportunity to control the bacteria they are developed to fight, for example Yersinia ruckeri.


The number of bacteriophages added to the water is such a small part of the total content of organisms in the water and will not affect the environment outside the hatchery in any way. By adding CUSTUS®YRS to the production water you will see a higher concentration of the bacteriophages for a short period until you start replacing the water. But it has an insignificant impact on the number of bacteriophages that is naturally being released from the hatchery daily.

What is biocontrol?

Biocontrol is the use of living organisms to decrease the population of unwanted organisms in biodiversity. With the help of CUSTUS®YRS you can control the infection pressure from the unwanted bacteria Yersinia ruckeri by reducing the amount of Y. ruckeri in the ecosystem. Other examples of biocontrol can be cleaner fish in salmon cages or ladybugs in a greenhouse.

Is it possible to use CUSTUS®YRS to treat sick fish?

No, that is not legal.

Can bacteriophages make you sick?

No, all living organisms are constantly exposed to a high number of different bacteriophages. For example, all cheese contains more than 1 billion bacteriophages per gram. The main role of bacteriophages in nature is to control bacteria population levels in an environment. This means that they are totally necessary in our existence. It is proven that people suffering from chronical intestinal infections, like Crohn´s disease, are in lack of specific types of bacteriophages.

Are bacteriophages alive?

The definition of viruses being living organisms is not clear from science yet. This is to be seen as a philosophical question.

How long will bacteriophages survive in the environment?

Bacteriophages are relatively stable in the water solution provided, if kept at a low temperature. They will be degraded by UV, ozone, high temperature, NaOH, chlorine, ethanol/disinfectant and proteolytic enzymes. Bacteriophages will quickly be diluted in the water, creating large distances between each other, therefore decreasing their chances of finding suitable hosts(bacteria). Fresh water bacteriophages will not be able to reproduce at sea.

Can the use of bacteriophages create any unwanted effects in the fish?

No. All fish constantly swim in high concentrations of different bacteriophages and are not harmed by this.

Why biocontrol and not medical treatment?

It has been documented that if bacteriophages are ‘involved’ throughout the period of a disease breakout, given enough time the pathogenic bacteria will naturally be suppressed. However, for this to happen a high concentration of pathogenic bacteria is necessary.


CUSTUS®YRS is added to the production water to lower the infection pressure in periods where the fish are more vulnerable to infection. This is so the phages can lower the number of bacteria BEFORE an outbreak even starts.


There are other applications such as burns and cystic fibrosis among humans where bacteriophages are being used as medical treatment. ACD Pharma is also working on other bacteriophage related drugs, but this involves other bacteriophages against another bacterium.

Will bacteriophages affect the water quality?

Yes, in a positive way. Naturally occurring bacteriophages help regulate the natural flora in the hatchery – they make sure that no single bacterium gets too dominant. Adding specific phages will only affect the bacteria they are specialiced to infect.

Can CUSTUS®YRS affect the activity of the biofilter?

No, CUSTUS®YRSonly attack the specific unwanted Yersinia ruckeri bacteria and have no impact on those wanted bacteria that is important for the biofilter.

Can I use antibiotics and bacteriophages at the same time?

Yes.

Can the bacteria develop resistance against bacteriophages?

Yes, bacteria can develop resistance against bacteriophages. This kind of resistance is independent from the resistance that can be developed against antibiotics, so there is no risk of increasing resistance towards anything other than that bacteriophage strain. Unlike chemical antibacterial agents, bacteriophages can evolve and develop countermeasures against the resistance. ACD Pharma uses a mixture of different bacteriophages towards the same bacteria, so if the bacteria develop resistance to one of them, the others will still kill the bacteria. The bacteriophages ACD Pharma decided to use are selected for low resistance development.

How can I remove the CUSTUS®YRS?

It is not necessary to remove the bacteriophages after use. CUSTUS®YRS bacteriophages will be diluted and washed out of the hatchery when the bacteria have been defeated and no longer exists as a “reproduction house” for the bacteriophages. All the other bacteriophages that naturally are present in the water will still be present, it won’t be possible or wanted to get rid of them.

Where can I get the CUSTUS®YRS?

Contact ACD Pharma, www.acdpharma.com. We will ask you to send in isolates of the bacteria/strains so that we can verify that your bacteria are sensitive to CUSTUS®YRS.

What is the price?

Water treatment with CUSTUS®YRS cost 130 NOK per m3 of water.

If the bacteriophages are so specific, how can I know that CUSTUS®YRS will work on the bacteria that causes problems at my hatchery?

The effect will be tested beforehand. Hatcheries that are interested in CUSTUS®YRS will be asked to send in a water sample with their Yersinia strain(s). These will be tested to see how sensitive they are against the CUSTUS®YRS phages.

What about my Debio-certification?

ACD Pharma is currently working on getting water treatment with phages approved for certified ecological production.

Can cross-reactions occur with other bacteria?

No. Bacteriophages in CUSTUS®YRS only infect Yersinia ruckeri. They are not capable of infecting other bacterial species in the fish or in the water.

Is this a drug or hygiene product or something else?

CUSTUS®YRS shall exclusively be used for biocontrol, not medicinal use under any circumstances.

What does the Norwegian Food Safety Authority say?

The Food Safety Authority has been well informed and is has a positive view on the use of bacteriophages. It is well documented that bacteriophages don´t have a negative impact on the welfare of the fish, and if the use of bacteriophages can reduce the occurrence of yersinosis bacterium and use of antibiotics, this is exclusively positive.

What does the Medicine Agency say?

ACD Pharma is working together with the Norwegian Medicine Agency and the European Medicine Agency on the use of bacteriophages in the future.

How long is the retention time?

Retention time only applies to drugs, and CUSTUS®YRS is not a drug.

What does the environmental Agency say?

The use of bacteriophages as biocontrol falls under the Food Safety Agency’s authority.

Can I use bacteriophages for decontamination/cleaning at my hatchery?

No. Bacteriophages are only for the use of reduced infection pressure under production. When you are cleaning or decontaminating your hatchery between each production cycle, other disinfectants like chloride will be cheaper and more effective.

How will bacteriophages affect other treatments?

Bacteriophages won’t have an impact on any medicinal treatment in the hatchery. Infact, the synergistic effect of bacteriophages and antibiotics is well documented in human medicine.

Can´t the fish get immune to bacteriophages?

This is not relevant due to the use of phages as biocontrol in the production water.