On Food and Cooking

generally don’t accumulate TMAO, and
crustaceans accumulate relatively little, so
they don’t get as fishy as ocean fish. In
addition, the unsaturated fats and fresh-
smelling fragments (aldehydes) produced
from them slowly react to produce other
molecules with stale, cheesy characters, some
of which accentuate the fishiness of TMA.
And during frozen storage, the fish’s own
enzymes also convert some TMA to DMA
(dimethylamine), which smells weakly of
ammonia.
Fortunately, the fishiness of fish past its
prime can be greatly reduced a couple of
simple treatments. TMA on the surface can be
rinsed off with tap water. And acidic
ingredients — lemon juice, vinegar, tomatoes
— help in two ways. They encourage the stale
fragments to react with water and become less
volatile; and they contribute a hydrogen ion to
TMA and DMA, which thereby take on a
positive electrical charge, bond with water