Morphological Variations of the Mudskipper Oxuderces nexipinnis (Cantor, 1849) in the Mekong Delta, Vietnam

This study provides data on the morphological variations of the mudskipper Oxuderces nexipinnis. A total of 616 specimens (223 females and 393 males) were collected continuously over a 12-month period (from August 2024 to July 2025) at four coastal sites in Vinh Long Province, Ca Mau Province, and Can Tho City. The analysis revealed that morphological traits such as eye diameter (ED), body depth (BD), head length (HL), and mouth width (MD) varied significantly between sexes, whereas interorbital distance (IO) showed no marked difference between males and females. All five traits (ED, IO, BD, MD, HL) fluctuated with season and ecological zone. The ratios ED/HL, IO/HL, BD/HL, and MD/HL were influenced jointly by sex, season, and sampling location. Notably, the interaction between sex and ecological zone had significant effects on ED/HL and MD/HL, indicating that sexual dimorphism in morphology varied across habitats. Moreover, the interaction between season and ecological zone strongly affected ED/HL and IO/HL, suggesting a potential morphological response to hydrological fluctuations and food availability between dry and wet seasons. These findings provide useful insights for species identification and enhance the understanding of ecological adaptation in O. nexipinnis within the Mekong Delta.