(trimethylamine) and the latter into kitchen-
cleanser ammonia. They’re thus responsible
for the powerfully bad smell of old fish.
Fish muscle tissues, shown in cross-section.
Below left: Most fish swim intermittently, so
their muscle mass consists mainly of fast
white fibers, with isolated regions of slow red
fibers. Center: Tuna swim more continuously
and contain larger masses of dark fibers,
while even their white fibers contain some
myoglobin. Right: Soles, halibuts, and other
bottom-hugging flatfish swim on their side.
Freshwater fish are a different story. Their
environment is actually less salty than their
cells, so they have no need to accumulate
amino acids, amines, or urea. Their flesh is
therefore relatively mild, both when it’s fresh