The toxicity comes from trimethylamine oxide (TMAO) which decomposes to trimethylamine (TMA), a neurotoxin. TMA is the compound that produces the odor most asso

The toxicity comes from trimethylamine oxide (TMAO) which decomposes to trimethylamine (TMA), a neurotoxin. TMA is the compound that produces the odor most associated with rotten fish and it's a very common metabolite found in many different animals (human gut and surface bacteria can produce it too). The Greenland shark and other ocean life have nervous systems and livers that are better adapted to handling higher concentrations of TMA because it plays an important role in regulating cellular osmosis, which is critical for both salt and fresh water animals. While this may be loosely related to their extraordinary lifespan, it's much more likely that this is an old adaptation from an ancestor species that is irrelevant to their longevity.