Morphological comparison of the feeding apparatus in herbivorous, omnivorous and carnivorous mudskippers (Gobiidae: Oxudercinae)

Oxudercine gobies show not only a full spectrum of habitat transition from water to land, but also varying feeding habits from herbivory to carnivory. In this study, we compared the anatomy of the feeding apparatus of five oxudercine gobies, Boleophthalmus boddarti (moderately terrestrial, herbivorous), Oxuderces nexipinnis (nearly aquatic, herbivorous), Scartelaos histophorus (moderately terrestrial, omnivorous), Periophthalmus chrysospilos (highly terrestrial, carnivorous), and Periophthalmodon schlosseri (highly terrestrial, carnivorous), collected from a mudflat in Vietnam. B. boddarti and O. nexipinnis are characterized by a horizontal disposition of the dentary teeth, more densely spaced gill rakers on the posterior row of the third arch and both rows of the fourth arch, and large, ventrally curved pharyngeal plates bearing numerous fine teeth. Ps. chrysospilos and Pn. schlosseri have oral jaw bones with jaw-levers producing a greater biting force, rudimentary gill rakers, and pharyngeal plates studded with robust canine teeth. On the underside of the ventral plates, prominent ridges occur, onto which strong muscles attach. The jaw adductors are larger in these carnivorous mudskippers. S. histophorus shows an anatomical architecture which may be considered intermediate between these herbivorous and carnivorous species. On the basis of currently accepted relationships of oxudercine genera, their feeding habits, and the morphology of the feeding apparatus, we hypothesize that the oxudercine gobies had been adapted to feeding microalgae in shallow water before expanding their niche onto land, and subsequently diverged to more specialized herbivorous ( Boleophthalmus ) and carnivorous groups ( Periophthalmus and Periophthalmodon ) feeding in higher intertidal habitats.