Morphological Descriptions of Shuttles Mudskipper Periophthalmus modestus (Gobiidae: Oxudercinae) at Early Life Stages from a Large Tropical Estuary

Species of the genus Periophthalmus are models for studies of adaptation to move from water to land as their pectoral fins have been modified for terrestrial locomotion. Periophthalmus modestus is an amphibious fish that occupies the estuaries, swamps and tidal mudflats of the Northwest Pacific from Vietnam to Korea and Japan. Larvae and juveniles of P. modestus are distributed in the Ba Lat estuary of northern Vietnam, but no morphological descriptions have been reported here. The present study used 50 specimens including 11 planktonic larvae, nine benthic juveniles, 22 amphibious juveniles and eight adults collected in that estuary from 2018 to 2020 to examine their morphological characteristics. These are the first descriptions of developmental characteristics of P. modestus from larval to juvenile stages collected from the wild. During their life stages, P. modestus is going through a turning point, at ca. 16 mm total length. At this turning point, P. modestus experiences dramatical changes in the position of eyes, which gradually move to the dorsal side, and the position of mouth, which moderately shifts to the ventral side. The occurrence of melanophores is also changed during transition stages. Present findings help to provide additional information to identify this species at their early life stages and further studies on larval and juvenile morphology of P. modestus.