Rapid temperature-dependent wound closure following adipose fin clipping of Atlantic salmon Salmo salar L.

Three groups of Atlantic salmon were kept at a constant temperature of 4, 10 and 14 °C. The adipose fins were removed; six fish/group were sampled at 11 subsequent time points post-clipping. Samples were prepared for histopathological examination to study the course of re-epithelization. A score sheet was developed to assess the regeneration of epidermal and dermal cell types. Wounds were covered by a thin epidermal layer between 4 and 6 h post-clipping at 10 and 14 °C. In contrast, wound closure was completed between 6 and 12 h in fish held at a constant temperature of 4 °C. By 18 h post-clipping, superficial cells, cuboidal cells, prismatic basal cells and mucous cells were discernible in all temperature groups, rapidly progressing towards normal epidermal structure and thickness. Within the observation period, only minor regeneration was found in the dermal layers. A positive correlation between water temperature and healing rates was established for the epidermis. The rapid wound closure rate, epidermal normalization and the absence of inflammatory reaction signs suggest that adipose fin clipping under anaesthesia constitutes a minimally invasive method that may be used to mark large numbers of salmon presmolts without compromising fish welfare.

Effect of temperature and diet on wound healing in Atlantic salmon (Salmo salar L.).

Compromised skin integrity of farmed Atlantic salmon, commonly occurring under low temperature and stressful conditions, has major impacts on animal welfare and economic productivity. Even fish with minimal scale loss and minor wounds can suffer from secondary infections, causing downgrading and mortalities. Wound healing is a complex process, where water temperature and nutrition play key roles. In this study, Atlantic salmon (260 g) were held at different water temperatures (4 or 12 °C) and fed three different diets for 10 weeks, before artificial wounds were inflicted and the wound healing process monitored for 2 weeks. The fish were fed either a control diet, a diet supplemented with zinc (Zn) or a diet containing a combination of functional ingredients in addition to Zn. The effect of diet was assessed through subjective and quantitative skin histology and the transcription of skin-associated chemokines. Histology confirmed that wound healing was faster at 12 °C. The epidermis was more organised, and image analyses of digitised skin slides showed that fish fed diets with added Zn had a significantly larger area of the epidermis covered by mucous cells in the deeper layers after 2 weeks, representing more advanced healing progression. Constitutive levels of the newly described chemokines, herein named CK 11A, B and C, confirmed their preferential expression in skin compared to other tissues. Contrasting modulation profiles at 4 and 12 °C were seen for all three chemokines during the wound healing time course, while the Zn-supplemented diets significantly increased the expression of CK 11A and B during the first 24 h of the healing phase.