Changes in hydrolytic enzyme activities of naïve Atlantic salmon Salmo salar skin mucus due to infection with the salmon louse Lepeophtheirus salmonis and cortisol implantation

[摘要] ABSTRACT: The changes in the activities of mucus hydrolytic enzymes and plasma cortisol levels were examined following infection of Atlantic salmon Salmo salar with the salmon louse Lepeophtheirus salmonis and these changes were comparedwith those resulting from elevated plasma cortisol. Salmon were infected at high (Trial 1; 178 ± 67) and low (Trial 2; 20 ± 13) numbers of lice per fish and the activities of proteases, alkaline phosphatase, esterase and lysozyme in the mucus, as well asplasma cortisol levels were determined. At both levels of infection, there were significant increases of protease activity over time (1-way K-WANOVA; Trial 1, p = 0.004; Trial 2, p < 0.001). On several sampling days, generally on later days in theinfections, the mucus protease activities of infected fish were significantly higher than control fish (Student¹s t-tests; p < 0.05). In addition, zymography experiments demonstrated bands of proteases at 17 to 22 kDa in the mucus of infectedsalmon that were absent in the mucus from non-infected fish and absent in the plasma of salmon. The intensity of these protease bands increased in the mucus over the course of both infections. However, plasma cortisol levels were elevated only in theheavily infected fish from the first trial. At high infection levels (Trial 1), alkaline phosphatase activity was higher in the mucus of infected fish at all days (t-test, p < 0.05). However, at the lower infection level (Trial 2), the mucusalkaline phosphatase activity did not differ significantly between infected and non-infected fish. Esterase and lysozyme activities were very low and did not change with time nor between non-infected and infected salmon in either challenge. Mucus enzymeactivities of cortisol-implanted salmon did not change over time, nor were there any differences in activities between cortisol-implanted and control salmon. The present study demonstrates biochemical changes resulting from sea lice infection of Atlanticsalmon occurring at the site of host-pathogen interaction, the mucus layer. However, the origin of these enzymes, whether host or pathogen, remains to be determined.

[学科分类] 生物科学（综合）

[关键词] Atlantic salmon;Salmo salar;Lepeophtheirus salmonis;Sea lice;Protease;Enzyme;Skin mucus;Cortisol