I was always perplexed about why there wasn't any good seafood restaurants in Chennai and why every place was trying to push basa in the name of maritime delights (ugh). Chennai is a coastal city with a fish eating culture - the fish monger has so many options but most restaurants have only a few: neithilly (fresh anchovies), king fish, prawns, crab sometimes, and a shredded shark meat preparation called suraputtu.
Marine, at college road, is an absolute revelation. They have their own trawlers, engage in "sustainable fishing", and have the complete array of fish that a fish monger has available, and then some. You pick the fish you want, and it is prepared as per your liking from the options available - including grilling it, curries, fries and even regional preparations like Meen moily and pollichattu (the former being a mild coconut based curry, the latter being a spicy masala fish, typically the pearl spot, that's seared in oil and then steamed in a banana leaf.) They can get a little carried away with the cooking bit, so you need to instruct the staff not to batter fry the fish if you don't want it that way. The best part about the Marina is that I've got to try a lot of fish that was unfamiliar to me (I used to live on the west coast). It's pricey - depending on what you order (the fish is charged per 100 grams) it comes to about 800-1000 bucks a person.
If anyone is visiting Chennai I'd definitely suggest you make this restaurant a part of your itinerary.