Health Challenges

Heart and circulatory health

Heart and circulatory health

Heart and circulation ailments represent one of the greatest challenges within fish health today. HSMB, CMS and PD are all viral diseases that affect the heart. In addition, we are seeing the occurrence of malformed and small hearts, and heart failure without any obvious cause. 

These ailments are threats both to fish health and fish welfare, and also lead to financial loss for the fish farmer due to reduced growth and increased mortality.

There are indications that unexplained background mortality at sea and increased mortality in connection with lice treatment and other major handling operations may be connected with reduced performance of the heart and circulatory system.

The salmon's circulation syste

The salmon's circulation system

The blood vessels are like the body's infrastructure network. The blood transports, amongst other things, nutrients, waste materials, hormones and oxygen, to and from the tissues and organs. Salmon have a simple circulation system. The heart has two chambers, and the blood travels one lap of the body.

Oxygen-rich blood is pumped from the heart to the gills where an exchange of gases occurs.

The fish emit CO2 into the water and take oxygen into the blood. From the gills, the blood is pumped into the body where it deposits oxygen and nutrients into the tissues before the now oxygen-rich blood is transported back to the hear for a new cycle. 



From nature's perspective, a wild salmon is an athlete that has adapted to a life with enormous physical effort. They live for large parts of their life wandering around the oceans and many salmon enter rivers and spawn several times. If we compare the heart of a farmed salmon with that of a wild salmon, it will be smaller and have a rounded and less suitable shape than a wild salmon. This also makes farmed salmon more susceptible to diseases that can weaken the function of the heart.

Both the size and composition of the muscles affect how effectively the heart contracts. In the same way that training and a healthy diet with an increased amount of omega-3 have been shown to improve heart health in people, studies have also shown that you can effect the construction, and therefore better heart capacity, with the help of training of smolt combined with an adapted diet in the form of feed with increased access to the beneficial omega-3 fatty acids

Risk behaviour

Risk behaviour

It can appear that farmed salmon can manage with this heart under normal conditions. The problems arise it situations where they have to deal with extra stress. With increased physical load and stress, oxygen use in the tissues increases and the heart has to compensate for this by transporting more blood through the gills and to the tissues.

Such physically demanding situations occur for example with delousing, during transportation and other forms of handling in the course of production. Over recent years, salmon have had to experience an ever-increasing number of delousings.

A farmed salmon's heart is less developed and has a lower pumping capacity than the heart of a wild salmon. They are therefore more susceptible to diseases that can put stress on, and damage, the heart.

HSMB and CMS are viral diseases that mainly affect the heart and PD also affects the heart to a greater or lesser degree. These diseases are geographically widespread,and can lead to damage to the heart muscles of Salmon.


HSMB: Heart and Skeletal Muscle Inflammation

HSMI stands for heart and skeletal muscle inflammation and is a disease that is connected with infection with Piscint Ortoreovirus (PRV).

The is one of the most frequently diagnosed diseases in Norwegian fish farming with 141 reported cases in 2014. The real figure is probably higher as the figure was removed from the list of reportable diseases midway through the year. 

First year at sea

HSMI often affects salmon in the course of their first year at sea and mortality varies up to 20%. The highest proportion of mortality is often seen in connection with operational procedures, as these expose the circulatory system of the fish to extra stress. If there is an outbreak of HSMI in a collection of livestock, fish farmers and fish health personnel must be especially vigilant of this when planning procedures such as delousing, sorting and similar. For example, this will influence the choice of agent used for delousing.

Reduced growth

In addition to the increased mortality, an outbreak of HSMI may lead to reduced growth. Fish affected by disease often have a poor appetite, and in addition, some of the energy they receive will go towards fighting the disease. This can therefore lead to poorer utilisation of the feed, an extended production period and therefore increased production costs.

In addition to the typical changes we see in autopsies on salmon that have died from HSMI, we will often find that the heart wall has thickened due to the infiltration of a large number of inflammatory cells. With an active outbreak of disease, we will also be able to find bleeding and inflammation in the skeletal muscles. 

There is currently no treatment for HSMI, but research indicates that you can influence resistance to and the degree of severity of the disease by changing the composition of fatty acids in the feed. The disease can also be prevented by reducing operational procedures that involve stress. (Source:

  • Where: Entire coastline, especially northern areas
  • When: Often during the first year at sea
  • Occurrence: Throughout the production phase – freshwater and seawater. 141 reported cases (-July 2015)
  • Problems of the disease: Small external changes, typical autopsy findings are consistent with heart failure: fluid in the cardiac and abdominal cavities, pale heart, pale or yellowish liver, swollen spleen, punctiform accumulations of blood in adipose tissues surrounding the organs. Bleeding can be observed in the skeletal muscles.
  • How feed can be used in disease control: Research has shown that the course of disease 
  • Our feed: Qardio
Photo: Trygve Poppe

CMS - cardiomyopathy syndrome

CMS stands for cardiomyopathy syndrome, which translates to ”disease of the heart muscles”. The disease is colloquially called "broken heart syndrome" as the typical autopsy findings are that the heart wall has torn or ruptured.

New virus

In 2010, CMS was associated with a new virus that was named Piscine Myocarditis Virus – PMCV, and the disease is characterised by the infiltration of large numbers of inflammatory cells into the heart muscles.

CMS outbreaks can lead to substantial financial losses for fish farmers as they affect salmon as they approach their harvest size. Then the fish farmer has to use substantial resources to ensure the salmon survive, both in the form of working hours that are used to care for the salmon, and for the use of feed. Mortality is on a par with HSMI primarily related to operational procedures, as the weakened heart is not able to withstand the increased physical stress it is exposed to. (Source:

  • Where: Entire coastline.
  • When: All year round, often affects large salmon and salmon close to slaughter size.
  • Occurrence: 107 reported outbreaks in 2014
  • Problems of the disease: Few external changes, often large and seemingly healthy salmon die with no visible changes.
  • How can feed can be used in disease control? Research has shown that the course of disease can be influenced by adjusting the level of fatty acids in the feed.
  • Our feed: Qardio




Pancreas disease (PD) is a serious viral disease that primarily affects the digestive system in salmon, although it can also lead to inflammatory changes in the heart.

Pale and ruptured hearts have been observed in connection with outbreaks. Examination of virus types with PCR have indicated the PD virus in the heart muscles, which can contribute to excluding the more classic heart diseases as the cause of the changes. 

Photo: Trygve Poppe