I am afraid of Manta ray while swimming in warm, tropical waters.
I got to swim with manta rays once. It was a great experience. Where can I usually find Manta Rays in the world?
They are mostly found in warm temperate, subtropical and tropical waters.
The ones I saw were very big. About how large can they grow?
They can be larger like the "M.birostris" or smaller like "M.alfredi".  Weren;t you scared of them?
A little, but once I got used to them I was fine. I didn't get to feed them though. What kind of food do they eat?
It seems that they are filter feeders and eat large quantity of zoopankton.
Are manta rays endangered?
Yes they are listed as vulnerable by the International Union for Conservation of Nature.