Abstract
Skin biopsies (5 mm) taken from behind the dorsal fin on Atlantic salmon post-smolts were followed over a 2 month period. The healing process was dominated by hemostasis, acute inflammation, and epidermal repair the first 14 days post wounding (dpw), as shown through imaging, histological evaluation, and transcriptomics. Most of the immune genes showed decreased expression after two weeks, approaching the levels of intact skin, as also reflected in sections where reduced inflammation in the wound bed was observed. Transcriptional events suggest recruitment of lymphocytes to the wound site during the acute phase, with activation of humoral responses from 14 dpw and onward. From the histology, a more adherent mucus was observed that correlated with altered transcription of glycosyltransferases. This may indicate different properties and functions of the mucus during the wound healing process. Wound contraction started between 14 and 36 dpw. The occurrence of these events was concurrent with granulation tissue formation, melanocyte migration and up-regulation of genes involved in extracellular matrix formation. The presented description of the wound healing processes in Atlantic salmon gives insight into comparative ulcerative biology in mammals and fish and provides both novel and updated knowledge that can be applied for improved best operational practices for fish welfare in aquaculture.
Highlights
The skin of Atlantic salmon (Salmo salar), is a coherent and dense barrier that protects the interior of the fish against the outer environment
Each fish was wounded with a 5 mm punch biopsy needle (Fig. 1a), and the wound healing process was followed intensively during the first week, with samplings at 1, 3 and 7 dpw and thereafter at 14, 36, 43 and 57 dpw
Measurements of the wound width showed that the wounds expanded during the early healing phase
Summary
The skin of Atlantic salmon (Salmo salar), is a coherent and dense barrier that protects the interior of the fish against the outer environment. Since the dermis consists of several structures and cell types such as scales, bone cells, dense and loose connective tissue, fibroblasts, pigment cells, and capillaries[16], complete regeneration depends on an orchestra of responses involving many cell types and tissues. This process is well studied in zebrafish, in which granulation tissue is already present at 2 days post wounding (dpw) and at 28 dpw the damaged skin is almost indistinguishable from intact tissue[6]. By combining several methods, including photography, histology, immunohistochemistry, scanning electron microscopy and transcriptomics, important phases in the wound healing process in the skin of post-smolt Atlantic salmon was elucidated
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