I think the fish it's holding is some kind of Mosquitofish, a member of the Gambusia genus. Click below to see the video I shot.
If you watch the video above, you see how fast and accurate this bird is with its long sharp bill. Remember this and never try to rescue an injured or trapped egret or heron unless you really know what you're doing. They'll try to stab your eye!
I'm hoping to post more short videos like this in the future. I've just started experimenting with my camera's video recording abilities and iMovie on my MacBook. It's a whole new world compared to photo processing!