Histological Analysis of Fish Skin

At trial end, skin samples were taken from 3 fish per tank to evaluate general structure and mucous cell density. Tissue samples were stored in 10% formalin pots (CellStore™ 20 mL Pots, CellPath). Embedding, sectioning, and staining of the tissue samples were done at the Norwegian Veterinary Institute in Harstad, Norway. In brief, the tissue sections were hydrated in water and stained with 1% Alcian blue (Alfa Aesar), 3% acetic acid for 15 min, transferred to 1% periodic acid (VWR) for 10 min, followed by Schiffs (Sigma-Aldrich^®) reagent for 15 min, 30 s in hematoxylin (VWR) before dehydration and mounting. The stained tissue sections were scanned with a Hamamatsu slide scanner (Hamamatsu) and uploaded to the Aiforia^® platform and analysed according to Sveen et al. (2021) (link).