DIRECTIONS
In a large pot of boiling salted water, cook the pasta until al dente. Drain.
In a large, deep skillet, heat the olive oil until shimmering.
Add the onions and garlic and cook over moderate heat until softened, about 5 minutes.
Add the crushed red pepper and tomatoes with their juices and bring to a boil.
Cook over moderately high heat, stirring occasionally, until the sauce is very thick, about 8 minutes.
Add the clam juice and simmer until the sauce is thickened and slightly reduced, about 5 minutes.
Season the fish with salt and stir it into the sauce.
Simmer for 2 minutes, until the fish is nearly cooked through.
Add the rigatoni to the sauce along with the parsley and cook for 1 minute, stirring to coat the pasta.
Serve right away.