Marisma in the Marina behind Plaza Neptuno, its been a while since I have been there, if they are not there they have another location on the south side at Naranjo and Carranza.
El Baracuda on the beach just south of Buenaventura in Centro.
Okay, so I'm not the biggest fan of the fish, but I did try one at Mariscos Mismaloya (yes a street vendor) and was blown away by all the different flavors. Still not entirely sure what it was that made it so good, but loved it just the same.