Go to Goa bhawan, you can try oh Calcutta or mahabelly
The Hong Kong Club is the first place I had sea food and just loved it you must try it too.
Swagat is the best option for sea food
Not sure about seafood but you can have amazing fish pakora at Ganesh in Karol Bagh
Yum yum cha
I would suggest Sanadige , Chanakyapuri.
Swagat at Defence Colony market is a good option