The water shaders transparency needs to have the right depth. How far are the fish beneath the water surface? Just a bit more beyond that will be a good setting. The bottom of the shader control window has the density parameters. This will control the coloring; the color here will be more dominate than the surface color based on the depth of the transparency. The density slider allows you to adjust this effect. You can add more color/s functions and vary the density.
I think the last part is also needed. Turn on the shadows. That will allow the ripples to be apparent on the fish. This will increase the render time.
All in all, this is a very good study. I would increase the light spread of the water shader. Let more of the ripples stand out.
