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Adjusting from freshwater to marine life, salmon need a robust immune system to make the transition.
Nofima scientists have now developed a test that measures the immune status of salmon smolts. The test can provide information that fish farmers can benefit from when putting salmon into the sea.
The results can help increase the chances of survival. Each year, about 15 percent of farmed salmon die after being transferred from freshwater tanks on land to net pens at sea. Most of these fish die shortly after transfer.
What is the test?
It’s a diagnostic test that measures the activity of 44 genes that are important for the immune system. A sample is taken from the gills or dorsal fin without injuring the fish.
“A few years ago we noticed that the immune system is weakened during smoltification. For this reason, we decided to develop a test to measure the immune status of salmon during smoltification,” says Aleksei Krasnov, senior scientist at Nofima.
To do this, Krasnov and his colleagues evaluated many genes and selected those that provide the most information about the immune status. Scientists collected large amounts of data from many different experiments conducted at Nofima.
Krasnov is unaware that anyone else has such a large and well-organized salmon gene expression database. The activity of the selected genes was analyzed in salmon from different fish farms, different fish groups and under different environmental conditions. From this data, the scientists developed a database that provided the basis for diagnosing the immune status.
Gene activity reveals the body’s blueprint
The genes give the body’s cells “orders” to produce proteins that have a specific function.
Genes can increase or decrease activity long before we can detect changes in fish condition. Scientists measure the activity of carefully selected genes to assess the immune status and health of salmon.
The scientists found the normal level of activity for each of the 44 genes in a fish in good condition. If the activity level is too high or too low, it can indicate poor immune status. This means they can now offer immune status testing on salmon smolt.
“We can see which fish are in good shape and which are not. We also know which fish appear healthy but are actually not,” says Krasnov.
Industry representative Dr. Gordon Ritchie, Group Manager Fish Health & Welfare at Mowi ASA, co-authored the latest article.
“The successful development of this novel technique provides companies with a new tool in the Smolt Quality Assessment Box to verify the immunocompetence and robustness of smolts prior to sea transfer. This tool for diagnosing immune status can also be used in future research projects on smolt performance and survival,” comments Ritchie.
Useful in other projects
Krasnov also sees the benefits of the test in other research projects.
“With the test at the CtrlAQUA research center, we tested whether different ways of producing large smolts in closed recirculation systems affect the immune status before they are transferred to the sea. The test showed that the immune status was the same for the different manufacturing processes. We also use the test in projects where nutritionists are investigating whether feed ingredients affect fish health,” says Krasnov.
Lund et al. Assessment of immune status in two cohorts of Atlantic salmon reared in different aquaculture systems (case study), genesVol. 13, 2022. DOI: 10.3390/genes13050736