Characterisation of Lumpfish (<i>Cyclopterus lumpus</i> L.) Skin and Development of a Digital Histomorphometric Tool to Analyse It

Lumpfish are commonly used as cleaner fish in the production of Atlantic salmon as a preventive measure against sea lice. This, and other procedures, are stressful and may harm the cleaner fish. In this work, lumpfish skin was studied to understand this organ better and to develop tools to analyse and monitor lumpfish skin health. Three different sample sets were used: preadult lumpfish from a land-based hatchery, adult lumpfish from a salmon farm and adult lumpfish before and after a delousing at a commercial salmon farm. We developed a digital histomorphometric algorithm in Aiforia to better quantify structures and measure skin features and to study the effects of delousing treatment on lumpfish skin. Results show that lumpfish skin is highly complex. The specific cells and their integrity are important for the fish to maintain homeostasis and protect against the outer environment. Damages in skin are induced during or after delousing, and these damages may make the fish more susceptible to secondary infections. The detected damages may be difficult to observe through visual inspections, and in-depth analyses at the cellular level may be needed to understand the impact of different stressors on lumpfish health.