http://www.the-scientist.com//?articles.view/articleNo/39332/title/Convergent-Fish-Fins/

Some researchers are looking at another morphological structure of modern day fish to investigate fish evolution.

“Adipose fins are small, fleshy and usually not as elaborately structured as other fins. Although some 6,000 species of fish—including trout, catfish, and salmon—have them, relatively few researchers have studied these structures in the last half-century.”

They plan to explore early changes that may be linked to the transition to tetrapods.  The beauty of cience is there is always another question!