Clean all types of fish and wash them under running water.
Remove the beards from the mussels, wash them well, and place them in a pot with a few ladles of water so that they open and release any sand inside.
Cut the dogfish into thick slices.
For preparing the sauce, choose a wide, shallow casserole dish that can fit the fish without overlapping.
Add the oil, finely chopped onion, and whole garlic to the casserole dish, heat slightly, and add the vinegar, letting it evaporate a bit. Then, add the wine and the washed, chopped parsley. Before the vinegar completely evaporates, add the tomatoes and a few ladles of fish stock or water. Season lightly with salt (and optionally chili pepper) and cook for 14-15 minutes (if you have squid, add it two minutes after the tomatoes, as squid requires a longer cooking time).
Now, evenly distribute all the other fish in the casserole dish, lightly salt, cover with the lid, and cook on low heat for 7 or 8 minutes. Then, remove the lid, add the mussels, and cook for another 7 or 8 minutes so that the fish is cooked and the sauce has reduced slightly.
Avoid touching the fish while it is cooking. To prevent it from sticking to the bottom, occasionally shake and tilt the casserole dish gently to distribute the flavors.
Toast the slices of bread, place them on the plate, and carefully serve the fish with the sauce.
