Abstract
This study examined changes in Atlantic salmon Salmo salar epidermal mucus proteins following short‐ and long‐term handling stress. Short‐term stress consisted of a single removal of fish from water for 15 s with long‐term stress consisting of daily removal of fish from water for 15 s over 21 days. In the long‐term handling stress study, there was a high level of individual variability with respect to mucus alkaline phosphatase, cathepsin B and lysozyme activities, with no correlation to treatment group. There was limited or no positive correlation between lysozyme, cathepsin B or alkaline phosphatase activities and plasma cortisol. There was a significant difference in lysozyme activity for both control and stressed fish at day 21 compared to other sampling days. In the short‐term study, there was again high variability in mucus enzyme activities with no difference observed between groups. Immunoblotting also showed variability in mucus actin breakdown products in both short‐ and long‐term handling stress studies. There appeared, however, to be a shift towards a more thorough breakdown of actin at day 14 in the stressed group. This shift suggested changes in mucus proteases in response to long‐term handling stress. In summary, there were correlations of some mucus enzyme/protein profiles with stress or cortisol; however, the variability in S. salar mucus enzyme levels and actin fragmentation patterns suggested other triggers for inducing changes in mucus protein composition that need to be investigated further in order to better understand the role of mucus in the response of S. salar to external stressors.