Fish or meen in Tamil, is what you have to eat here in Mahabalipuram as they are catched in the morning or night and freshly served.
There is a lot of variety and if you allow me for those people who are not really fish-minded to reccomend shark, tasting almost like chicken.
More expensif are the prawns especially the Tiger-prawns, lately breeded in fish-farms using the seawater, but still an exquisite delight.
Another very fine fish you have to try is the King-fish, not always available as these are catched at night with long not-high nets (1km) with mesh sized their head.

So up to Mamalla to have a nice fish dinner !
Renown restaurants are plenty here.