Jimmy learnt about X-Ray fish today at Ms. Pam's Twinkling Stars preschool. At first I thought it was a fish under X-Ray, and I don't quite believe what he is saying. Then Google helped. It turns out to be a little fish that is quite transparent. From Wikipedia, "Pristella maxillaris, the only species in the genus Pristella, is commonly known as the golden pristella tetra or X-ray tetra because of its highly transparent body."