Scientists have developed a health test for smolts

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Salmon that must adapt from a life in freshwater to a life in saltwater need a robust immune system to make the transition.

Nofima scientists have now developed a test that measures the immune status of salmon smolt. The test can provide information that fish farmers will benefit from when transferring salmon to the sea.

The results can help increase the chances of survival. Each year, approximately 15% of farmed salmon die after being transferred from freshwater tanks on land to net pens at sea. Most of these fish die shortly after being transferred.

Senior Scientist Aleksei Krasnov.

What is the test?

This is a diagnostic test that measures the activity of 44 genes important to the immune system. A sample is taken from the gills or dorsal fin without harming the fish.

“A few years ago we found that the immune system was weakened during smoltification. As a result, we decided to develop a test to measure the immune status of salmon during smoltification,” explains Aleksei Krasnov, Principal Investigator at Nofima.

To do this, Krasnov and his colleagues evaluated many genes and selected those that provided the most information about immune status. Scientists have compiled large amounts of data from many different experiments performed at Nofima.

Krasnov is unaware that anyone else has such a large and well-organized database of salmon gene expression. The activity of the selected genes was analyzed on salmon from different fish farming sites, different groups of fish and different environmental conditions. Scientists used this data to develop a database that served as the basis for diagnosing immune status.

Gene activity reveals body blueprint

Genes give “orders” to cells in the body to produce proteins that have a given function.

Genes can increase or decrease activity long before we can see 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 may indicate poor immune status. This means that they can now offer tests for the immune status of salmon smolts.

“We can see which fish are in good condition and which are not. Also, we know which fish look healthy, but in reality are not,” says Krasnov.

Industry representative Dr Gordon Ritchie, who is Group Manager Fish Health & Welfare at Mowi ASA, co-authored the latest article.

“The successful development of this new technique offers companies a new tool in the smolt quality assessment box, to check the immune competence and robustness of smolts before they are transferred to sea. immune may also be used in future research projects on smolt performance and survival,” comments Ritchie.

Engineer Marianne HS Hansen of Nofima's lab analyzed large amounts of genetic material to build a database of gene activity, which forms the basis of the test.

Engineer Marianne HS Hansen of Nofima’s lab analyzed large amounts of genetic material to build a database of gene activity, which forms the basis of the test.

Useful in other projects

Krasnov also sees the benefits of using the test in other research projects.

“We used the test from the CtrlAQUA research center to test whether different ways of producing large smolts in closed recirculation facilities affected immune status before sea transfer. The test showed that the immune status was the same for the different production methods. We also use the test in projects where nutritional scientists study whether feed ingredients affect fish health,” says Krasnov.

Reference:

Lund et al. Evaluation of the immune status of two cohorts of Atlantic salmon reared in different aquaculture systems (case study), Genoa, flight. 13, 2022. DOI: 10.3390/genes13050736

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