We have discussed this before. I was going to address Truethat's three dozen or so posts that state that Amanda and Raffaele couldn't remember what happened the night before, but since you're doing it, too, I might as well just answer yours and hope Truethat reads it.
The only evidence we have of what the police asked Amanda about on the 2nd, 3rd or 4th of November is contained in her e-mail home:
http://perugia-shock.blogspot.com/2009/02/from-amanda-knox.html
There is no evidence in that e-mail that the police asked Amanda or Raffaele anything about themselves, or where they were or what they did on the night the murder took place. The police may have asked them about it, but we don't have any evidence of that, so we can't assume it.
If the police spent all their interview time on questions about Meredith, then it is not the least bit hard to believe that Amanda and Raffaele would have been focused on Meredith and on the day the body was discovered, rather than on what they did the night of the 1st. By the time they were interviewed about it on the 5th, it is very likely they would have forgotten many details, such as the time they ate, or what times they slept.
No, if I went out and bought and cooked fish, I would not remember it four days later. I haven't seen any evidence that they gutted a fresh fish. I suspect the "fish blood" remark belongs in the same category with the "pricked Meredith" remark -- made on the advice of lawyers, just in case.