Mrudul, about 1/2000 of a second.

Kiran, I was not waiting for this bird to fish, but Brahminy's do have a propensity to repeatedly hit the water. As Sabyasachi said, we usually see them moving away. This happened just in front of me, which brings me to my adage that the number of good images is directly proportional to time spent in the field.

Apana