Composition is the key here. First off, reviewing the actual content, it's a pretty funny cartoon. The reference to Finding Nemo are all there and very clear, without being unoriginal or a caricature.
I enjoy seeing a variety of art from you and while I love your creature concepts, this cartoony style fits you well, too.
What I like most about this picture is how well you used the composition to emphasize the joke of your drawing. The shark is rather even, blue in blue, not standing out from the background very much. The only real attention it attracts on first view is to the highlight in the eye and to the tooth, which is good because that puts the facial expression in focus of the viewer. The clown fish however is more dynamic, with folds, in strong contrast to the background and high contrast coloring. The fins are spikey and if that's not aggressive enough, the face with its pulled-up lips and the dark under-eye circles do the rest. The position of the fish add to the intimidating feel of the clown fish. Even the background with the swarm and the colorful plants draws more attention to the right side more than to the left side. Thus emphasizing the small fish as main focus.
I think the bubbles are a nice addition to show how angry he really is. lol
The only tiny little thing I would have liked to see would be some underwater light you usually see shining through from above in the upper background. Since parts of the background seem a bit boring. Hard to explain, I guess you know what I mean, but you can just google underwater light, if you are curious.
Overall, very good job. I like it.
