[Zbrafish] question about peroxide block IHC/ISH

[Serena]

I have a question about hte need for a peroxide block step in ISH. I
have seen many whole mout protocols for IHC that require a peroxide
block step to block endogenous peroxidases, however, the whole mount
in situ protocols that I have seen do not have one, despite the
similar AP detection chemistry. Can someone explain the reason for
this? I am performing in situ on rather old embryos 10-15 days (for
sectioning) and want to make sure I do not get a lot of background.

Also, if anyone has experience with this technique on this age range,
could you suggest a length of time for the proteinase K step.

Thanks!