Agua, Apex City Hotel

No, you're right enough - that's AGUA, with a "g", even though this restaurant is all about the creatures of the deep AQUAtic. Set within the Grassmarket's Apex Hotel, Agua is one of the few Edinburgh venues to have its own crustacean bar. If that sentence led you to expect scenes of crabs sipping cocktails, The Skinny won't spoil the dream (suffice to say, however, it's something very different).
While it's not exclusively sea-food, Agua is rightly famed for its irresistibly flavoured and impeccably presented fish dishes, and is worth sampling for the Shetland smoked salmon salad alone.
Thankfully, the desserts are fish-free.