As others have said - the action catches the fish, but as an artist myself, I can see the need to create more realistic finishes. It's just a personal thing. So with that I'll offer some constructive criticism.
Blend your colors (as madbass already stated.) Put less paint on your brush/sponge and gradually apply color as you transition from one color to the next. It takes practice and a lot of touch. If you can learn this now, when you get an airbrush, it will make it much easier.
Although not too important, you could paint some extra details like fins or the big black dot on the gill (not sure what that's called.)