You could kick a football on Bajo de Guía and guarantee it'd land on a decent plate of fish, but you should probably aim for Poma, where the frito variado (€15) arrives loaded with lightly fried species plucked out of the nearby sea and river. Seafood stews, grilled fish and arroz a la marinera for two are also popular.
Poma
Sanlúcar de Barrameda