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.