The picture of the fish is of a bad quality really, which is why we need to improve it a little. Firstly we have to copy its layer: Layer ? Duplicate Layer (ctrl+j), decolorize the copy: Image ? Adjustments ? Desaturate (shift+ctrl+u) and apply on this layer the filter next shown: Filter ? Other ? High Pass.



Change the layer's Blending Mode on Overlay and combine the layers with the fish: Layer ? Merge Down (ctrl+e).



Make another copy of the layer and apply to this copy another filter's option: Filter ? Noise ? Median.



Change the layer's Blending Mode on Soft Light and minimize the layer's Opacity till 45% and then correct the layers again (ctrl+e).