Transportation of live fish is a common practice among aquaculture facilities. Many studies have previously
reported how transport elicits physiological stress responses and increases disease susceptibility in farmed
fish. The aim of this work is to investigate the changes that the skin of rainbow trout (Oncorhynchus mykiss)
experiences due to stress. Since NaCl is commonly added to transport water as a stress mitigator, the effects of
salt addition on the skin mucosa and skin-associated bacteria were also examined. Three experimental groups
(Control, post-transport no salt (PTNS) and post-transport with salt (PTS)) were analyzed in a 5-hour transport
acute stress model. Results indicate that the skin mucosa and the skin-associated bacteria are affected by transport
stress. Total numbers of culturable skin-associated bacteria increased by ~10-fold and ~50-fold in the PTS
and PTNS groups, respectively. Compared to controls, MUC2 expression was increased by 5-fold and 2-fold in
the PTNS and PTS groups, respectively. Claudin-7, 8d and 12 expression levels were higher in both PTNS and
PTS groups whereas antimicrobial peptide gene expression was lower than controls. Expression of the antiinflammatory
cytokine TGF-β but not IL-1β, IL-6 and TNF-α was up-regulated 2–3 folds in both the PTS and
PTNS groups. The addition of salt diminished some of the physiological responsesmeasured including the numbers
of skin-associated bacteria. The responses recorded here appeared to be efficient at controlling bacterial
translocation since stress did not lead to significant presence of bacteria in the liver or spleen of rainbow trout.
When examining the ability of skin mucus to inhibit or promote growth of the bacterial pathogen Vibrio
anguillarum, the skin mucus of PTS trout was more efficient at inhibiting V. anguillarum growth (20% inhibition)
compared to control or PTNS mucus (11–12% inhibition). Our data clearly indicate that the skin and skin microbiota
of rainbow trout undergo important physiological responses during stress. The reduction in themagnitude
of the skin responses recorded when saltwas added to the transport water explains a newmechanismbywhich
salt is an effective stressmitigator in somefish species. Aquaculture specialists will benefit fromthe present study
by taking into consideration the importance of skin health during live transport.