Bring the fish broth to a rapid boil, and stir in a little salt and pepper.
Add the tomato paste, and stir to incorporate thoroughly.
Sprinkle in the manioc flour, a little at a time, stirring vigorously and continuously until all the flour has been incorporated and the mixture has the consistency of soft ice cream.
Serve immediately; like polenta, pirao gets stiffer the longer it sits.