Molecular evidence for stress, inflammation and structural changes in non-specific ulcers in skin of farmed Chinook salmon (Oncorhynchus tshawytscha)

Fish skin is critical to physical defence against pathogens and there is a need to understand the physiological processes impacting ulcers and their healing. Ulcers have been reported in farmed Chinook salmon in New Zealand. This study investigated stress, immune and structural gene expression in farmed Chinook salmon skin with and without ulcers from two sites in New Zealand sampled from February (higher temperature, late summer) to May (lower temperature, late autumn). Skin samples taken adjacent to non-specific ulcers in May and control fish in February demonstrated upregulation of heat shock protein 70 relative to control fish in May. Anterior gradient 2 expression was upregulated in fish with ulcers relative to control fish (both February and May), suggesting increased mucous cell activity. Based on the results of this study, fish with non-specific ulcers showed evidence of stress, inflammation, re-epithelisation, and delayed healing near the ulcer site, elucidating the importance of these processes in the pathogenesis of non-specific ulcers in farmed chinook salmon. •Collective transcriptional profiles of normal skin, ulcers and healing ulcers were distinct.•Significant upregulation of heat shock protein70 expression in February and ulcer control in May compared to control in May.•Significant upregulation of mucin 5 was observed in control fish in February compared to May.•Anterior gradient2 expression was upregulated in fish with ulcers relative to control fish.