Salmon benefits from being prepped with zinc and omega-3 before they are transferred to seawater. The same may also apply before they are treated for lice, moved to cold water or other stressful event that it is a challenge for skin health.
Scientists at Nofima have conducted a project to evaluate how different levels of zinc and marine omega-3 fatty acids (EPA and DHA) in feed affect function, barrier properties and wound healing processes in salmon skin. The salmon were studied through smoltification in freshwater, transfer to salt water for ten weeks and were fed with different levels of zinc and omega-3 ranging between 100 and 300 mg of zinc and 0.5 and 2 grams of omega-3 fatty acid per kilo of feed.
Fish that had received higher doses of omega-3 and zinc coped with the transfer to sea water better. While high levels of marine omega-3 strengthened the lower skin layers, through thicker connective tissue and fat layers, high levels of zinc affected the outer layers in that the outermost layer, the epidermis, became smoother and contained more mucous-producing cells. These differences seem to affect the fish’s skin strength and ability to withstand external stresses. Wounds on fish that had received high levels of zinc and omega-3 in the feed healed faster than those on fish that had received lower levels.
There is an upper limit for zinc in fish feed, Current EU regulations allow maximum of 180 mg of zinc per kilo. Less than 50 % of dietary zinc is absorbed by fish, and unabsorbed zinc might reach harmful levels when emitted to the environment.