Do fish have fingers?

After a reminder of the important concepts developed in the fourth lesson, the function of Hox genes during teleost pectoral fin development is discussed, with loss-of-function experiments. Next, a recent study is described in which, following gain-of-function genetic screening, bony pieces are added distally to proximal radials, suggesting an intrinsic ability of the fish endoskeleton to generate additional elements in the distal face, as is the case in tetrapod limbs. Two studies involving the paddlefish (polyodon) are then detailed, showing general characteristics similar to those described in zebrafish. In this context, the benefits but also the problems of working with non-model species are briefly mentioned.