Modification of pectoral fins occurs during the larva-to-juvenile transition in the mudskipper (Periophthalmus modestus).

Our results show that the localized cell division of the proximal part of the endoskeletal disc-the primordium of the proximal radials-and subsequent cell division along the proximal-distal axis, which is restricted to the distal part of the disc during the larva-to-juvenile transition (metamorphosis), lead to the elongation of the proximal radials.