I like this. This is cute. You've got a good grasp of lighting and general shape.
Since it's an icon, I'm assuming that you're going to be viewing this at size rather than zoomed in or anything, so with that in mind: it's very difficult to see the dorsal fin. I'd also perhaps make the eyes a bit friendlier and more cartoony rather than just squares like you've got right now. You also have a LOT of colours in the background - you can't really see that gradient from so far out. Some other colours, like the highlights and the belly, work well as the same colour, too. I did a quick edit that might give you some ideas. I changed up the colour ramp a bit in my edit - the darker colours are a bit bluer, while the lighter colours are leaning towards yellow and green. This gives a better sense of depth.