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

Background: Mudskippers are amphibious fishes that use their pectoral fins to move on land. Their pectoral fins are specifically modified for terrestrial locomotion. Studies of the anatomy and kinematics of adult mudskippers suggest that modifications of the pectoral fins, such as their protrusion and elongation of the proximal radials, may provide greater control and flexibility in pectoral fin-based locomotion. However, it is unknown when and how the unique features of these pectoral fins form during the development of mudskippers, which begin life as a planktonic organism.

Results: Here we examined the developmental process of the pectoral fins of the mudskipper Periophthalmus modestus to address these questions. We also observed other developmental characteristics to provide clarified descriptions, including indicative morphological changes that occur during metamorphosis.

Conclusion: 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.