Lovely, I wish I could use oil paint like that!
I think you did a grate job in the lighting, but not so much the shading.
I can hardly notice the waves in this picture. I now it may not seem important, but if you could bring out the waves better, add more shadow and light to them, it'd move the viewer's eyes around the picture and they'd appiciate all the detail a little bit more.
Also if you moved the fish a little further to the... (I want to say 'corner' but there are none in this picture) ...top left of the painting, and made the waves more wild. I think it's become something really impressive.