ISSUE FOCUS 52 FEED & ADDITIVE MAGAZINE March 2025 “Osmolytes help regulate fluid exchange, and one particularly potent osmolyte is Trimethylamine-N-oxide, commonly known as TMAO. This molecule not only helps salmon maintain fluid balance but also protects them from protein denaturation during pressure changes as they move up and down the water column, making it a vital adaptation for marine species.” Winter is a challenging period for farmed salmon, as cold temperatures significantly impact their metabolism, causing all physiological processes to slow down. This slowdown affects processes like digestion, immune responses, and the recovery time of the skin and mucosal layers following procedures that compromise their integrity. Consequently, fish health is particularly vulnerable during this time. Recently, another critical physiological process linked to reduced fish robustness in winter has been identified—not only does their eating slow down, but their drinking does as well. THE ROLE OF FLUID BALANCE IN MAINTAINING FISH HEALTH The seawater surrounding salmon is much saltier than the fluid inside their bodies. The skin acts as a barrier to prevent dehydration, which occurs when water is drawn out of the fish into the surrounding environment through a process called osmosis. Despite this barrier, some water is lost, and salmon have developed strategies to maintain a healthy fluid balance between their bodies and the sea. One of these strategies is drinking. Salmon continuously drink seawater and excrete excess salts through their kidneys, gills, and secretions along the gastrointestinal tract. However, as mentioned earlier, drinking slows down during winter, so the fish rely on another strategy to maintain fluid balance: increasing the levels of osmolytes in their bodies. Osmolytes help regulate fluid exchange, and one particularly potent osmolyte is Trimethylamine-N-oxide, commonly known as TMAO. This molecule not only helps salmon maintain fluid balance but also protects them from protein denaturation during pressure changes as they move up and down the water column, making it a vital adaptation for marine species. TMAO has previously been linked to fish health. In 2000, Rørvik and collaborators published trials investigating the effects of TMAO and urea supplementation in feed on improving skin health and reducing ulcers in rainbow trout. In the study they also observed reduced fat belching and improved lipid digestibility. The positive observations on the digestive system have further been supported in a recent study by Bockus and collaborators exploring the effects on TMAO supplement in Rainbow Trout. Growing evidence now highlights TMAO as a vital component in marine ingredients that THE POTENTIAL ROLE OF TMAO IN MITIGATING FISH HEALTH CHALLENGES DURING WINTER Marianne Nergård Product Director Aker QRILL Company
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