It's just a radial blur set on zoom. Takes some messing around with to get it right but it works pretty darn good!
You want to select the image you want to stay clear with the marque tool. Then under the "select menu", depending on what version of PS, select "feather". I set mine to 15 for a 600 pixel wide image. Select OK. Then inverse the selection. Now everything but the fish is selected. This is when you go to the "filter menu" and select "blur" and then "radial blur". From there I start from 5 to 10 and set it on zoom. That's all there is to it. I use PS cs3 so it might be a little different in other versions.