of cod, bluefish, and other species often suffer
from some degree of gaping, separations of
muscle layers through which heat penetrates
more rapidly. Such fish as tuna, swordfish,
and shark have very dense flesh, crammed full
of protein (around 25%), which absorbs a lot
of heat before its temperature rises; less
active members of the cod family get by with
less protein (15–16%) in their muscle, and
cook more rapidly. Fat transfers heat more
slowly than protein, so fatty fish take longer
to cook than lean fish of the same size. And
the very same species of fish can be protein-
or fat-rich one month, depleted and quickly
heated the next.
There are several ways to work around
these inherent obstacles and uncertainties:
Cook the fish through with the gentlest
possible heat, so that the outer portions
aren’t badly overcooked. Oven baking
and poaching well below the boil are two
good ways to do this, after an initial and