There are lots of things going on in this picture I don't get.
What's the blue line around the fish?
Why is the water line so slanted?
Why are you including the very bright area at the top? (it draws my eye)
My impression is that there is a real lack of detail here and the hippo itself isn't very well captured so the hippo and fish part of the picture doesn't come across.
The shutter speed is way to slow for this focal length to hope to get good detail on soemthing moving.