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Effects of low to very high water velocities on Atlantic salmon post-smolts: Part II: Welfare, mucosal health and stress responses

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Kjetil Aune


8th International Symposium on Aquatic Animal Health; , 2018-09-02–2018-09-06

Lazado, Carlo C.; Gerrit, Timmerhaus; Timmerhaus, Gerrit; Nikko Alvin, Cabillon; Britt-Kristin, Reiten; Lill-Heidi, Johansen

There is ample evidence showing the beneficial effects of induced swimming, or exercise training in farmed fish. In Atlantic salmon, it has been shown that training through elevated water velocities has positive impacts on growth, feed conversion efficiency and robustness. However, there is little evidence demonstrating the effects on mucosal and stress responses, as well as on the external welfare of fish. More so, there is a question whether limits exist on the beneficial functions of elevated water velocities in salmon. In this study, we subjected salmon post-smolts (initial body weight circa 80 g) to four different training intensities by manipulating the water velocity in the tank: low – 0.5 body length per second (BL/s); medium – 1.0 BL/s; high – 1.8 BL/s; and very high – 2.5 (BL/s), for three months. The water velocity in the very high group has not been tested before in salmon. The external welfare status of fish was assessed following the FISHWELL handbook. Increased incidence of skin damage (i.e., scale loss, hemorrhaging) and pelvic fin damage (i.e., splitting) in the high and very high groups was documented. Nonetheless, the overall external welfare scores remained favourable in all groups. The skin and gills were subjected to quantitative histomorphometry and qPCR analysis of genes relevant to the mucosal defence. The expression of immune defence genes (e.g., cd8α, tcrα, mhc1, mhc2, mblc2) in the skin was negatively affected in the very high group, where significantly lower transcript levels compared with the other groups were observed. Interestingly, no significant differences between treatments were observed in the expression of selected marker genes in the gills. Histomorphological analyses of skin and gills are on-going. Plasma samples were collected and analysed for stress indicators. Plasma cortisol, glucose and lactate varied remarkably between groups at the beginning of the trial but such differences were not observed at the termination of the experiment. In conclusion, the welfare scores and the gene expression results in the skin revealed that the very high velocity may have some unfavourable consequences. Nonetheless, results from other response variables are suggesting that salmon subjected to a water velocity higher than the level previously thought to be the upper limit does not pose substantial negative consequences to health and welfare. The results of the study offer new frontiers in producing robust salmon through the benefits of induced swimming at higher water velocities.