On Food and Cooking

way of maintaining their body fluids at the
right concentration of dissolved substances.
Water in the open ocean is about 3% salt by
weight, while the optimum level of dissolved
minerals inside animal cells, sodium chloride
included, is less than 1%. Most ocean
creatures balance the saltiness of seawater by
filling their cells with amino acids and their
relatives the amines. The amino acid glycine
is sweet; glutamic acid in the form of
monosodium glutamate is savory and
mouthfilling. Shellfish are especially rich in
these and other tasty amino acids. Finfish
contain some, but also rely on a largely
tasteless amine called TMAO (trimethylamine
oxide). And sharks, skates, and rays use a
different substance: slightly salty and bitter
urea, which is what animals generally turn
protein waste into in order to excrete it. The
problem with TMAO and urea is that once the
fish are killed, bacteria and fish enzymes
convert the former into stinky TMA