Mix lemon juice, olive oil, thyme and some black pepper together; place the fish slices in a shallow dish and pour over the marinade. Cover and leave for 1-4 hours.
Wash the mussels in cold salted water, discarding any that are not tightly shut. Place them in a saucepan with 150 ml (¼ pint) of the wine, the same of water, and 1 tablespoon of the shallots. Cover, bring to a boil, and con