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 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.
THE SALMON'S LIFESTYLE DISEASES
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
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.