In zebrafish, the blood vessels of the anal fin develop from lymphatics by transdifferentiation. Karina Yaniv presented unorthodox, but very compelling data supporting this conclusion last September at the Kloster Seeon Angiogenesis meeting.
Now her paper has been published in Nature. Interestingly, but understandingly, she doesn't really discuss in detail the relevance of her data in the context of the Secondary Vascular System (SVS), which is a specialized compartment of the cardiovascular system in fish. Kari Alitalo and I are doing exactly that in our News & Views discussion of her article. We hope to get lots of constructive pushback from everybody who doesn't agree with our interpretation, that the blood vessels that Karina describes are identical to those of the SVS.