Carla & John,

Here's some zebrafish-specific information that may affect your decisions
on what to
do next:

The zebrafish very often has a thick layer of adipose tissue right under
it's skin.
My presumption is that this may affect the penetration of your postfix.
When I do
paraffin sections of the fish, I use Bouin's or an alcohol-based formalin fix
(Davidson's or Dietrich's), presumably to increase penetration.  Of course
these
fixes are not useful for EM.  If John or the other experts think the
penetration will
be affected by this layer of adipose tissue, you may want to skin the fish
before you
post fix.  It's relatively easy to skin a fixed zebrafish.  I just make a
few cuts in
the skin at the back of the head, and use forceps to peel off the skin and
underlying
layer of adipose tissue.

Will this adipose tissue affect the penetration?

Karen in Oregon