September 20, 2022

 

Nofima scientists develop method for examining immune status of salmon smolt
 

 

Scientists from Nofima created a new method for assessing the immune status of salmon smolt, giving researchers and farmers a better idea of how the fish will adapt to seawater.

 

The test can provide information that fish farmers will benefit from when transferring salmon smolt from freshwater to the sea. The results can help increase the smolts’ chances of survival.

 

Every year, approximately 15% of farmed salmon die after being transferred from land-based freshwater tanks to net-pens at sea. Most of these fish die shortly after being transferred – making the test highly relevant for the industry.

 

Nofima has developed a diagnostic test that measures the activity of 44 genes that regulate the immune system. A sample is taken from the gills or the 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," said Aleksei Krasnov, senior scientist at Nofima.

 

To do that, Krasnov and his colleagues evaluated multiple genes and selected those that provided the most information about immune status. The scientists compiled large amounts of data from different in-house experiments at Nofima.

 

The activity of the selected genes was analysed from various fish farming sites, different groups of fish and different environmental conditions. The scientists used this data to develop a database that provided the basis for the diagnostics of the immune status.

 

The genes give 'orders' to the body's cells to produce proteins that have a given function. Genes may increase or decrease activity long before one can see changes in fish condition. Scientists measure activity of carefully selected genes for assessment of salmon immune status and health.

 

The scientists identified the normal activity level for each of the 44 genes in fish that are 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 immune status in salmon smolt.

 

"We are able to see which fish are in good condition and which are not. In addition, we know which fish seem healthy, but in reality, are not," Krasnov said.

 

Industry representative Dr Gordon Ritchie, who is group manager (fish health and welfare) in Mowi ASA, is co-author on the latest article.

 

"The successful development of this novel technique provides companies with a new tool in the smolt quality assessment box, for verifying the immune competency and robustness of smolt before transfer to sea," Ritchie said. "This immune status diagnostic tool can also be utilised in future research projects on smolt performance and survival."

 

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

 

"We used the test in the CtrlAQUA research centre to test whether different ways of producing large smolt in closed recirculation facilities affect immune status before transfer to sea takes place," Krasnov said. "The test showed that immune status was the same for the different production methods. We also use the test in projects where the nutrition scientists investigate whether feed ingredients affect fish health."

 

- The Fish Site