Atlantic salmon ( Salmo salar ) is one of the most economically important species of the aquaculture industry, with Nordic countries representing some of the major producers. Given its economic importance, an increased number of companies are implementing the use of recirculated aquaculture systems (RAS) for the production of Atlantic salmon. Throughout a production cycle in RAS, fish are subjected to a variety of stressful events, including transportation. In the case of Atlantic salmon, previous studies have focused on investigating the impact of truck transportation and transfer to sea on the health and stress status of the fish. However, information on the effect of pumping (e.g. from one tank to another) on S. salar is scarce. For this reason, the present research has focused on studying the impact of fish pumping on S. salar smolts in an industrial RAS, as well as their ability to return to basal levels, investigating the biochemical profile in the plasma, as well as the expression of relevant stress-related and immunoregulatory genes in a wide range of organs.
Salmo salar smolts were collected from an industrial RAS around a fish pumping event, transporting the fish from one tank to another. The sampling points were the following: 1) Three days before transfer; 2 ) During transfer; 3) 1h post stress (hps ); 4 ) 24hps; 5) 7 days post stress (dps ); 6) 14 dps. At each point, 8 individuals were sampled for blood, gills, liver, gut, and head kidney. Plasma was obtained through centrifugation of the blood for the characterization of the biochemical profile, and organs were destined to RT-qPCR analyses. The investigated biochemical parameters included cortisol, glucose, and indicators o f hepatic health, whereas the researched genes included gr1 , mr , muc2 , il1β , and tnfα.
The results displayed a significant increase in cortisol, with a slightly shifted increase in glucose levels, as predicted, indicating that fish suffered from stress during the pumping event, and the detected values of cortisol and glucose returned to basal levels in a matter of days (Figure 1). Furthermore, the expression of some genes related to the stress and immunoregulatory response was significantly affected by the process.