Pharyngeal Morphology of Round Goby (/Neogobius melanostomus/) and Tubenose Goby (/Proterorhinus semilunaris/) from Presque Isle Bay, Lake Erie

Abstract:

The objective of this project was to compare pharyngeal morphology of round goby (Neogobius melanostomus; RG) and tubenose goby (Proterorhinus semilunaris; TG) from Presque Isle Bay. Both species are native to the Ponto-Caspian region of Eurasia and have been present in the Great Lakes for more than 30 years. Of the two species, RG has been more successful expanding its invaded range, often into diverse habitats. Colonization ability of non-native species is often related to their ability to exploit food resources, and numerous studies have described food habits of RG and TG. Although both species prey on a diversity of insects and crustaceans, RG often prey heavily on mollusks, including dreissenid mussels. These differences in food habits may be due to differences in the pharyngeal apparatus which consists of modified gill arches used to process food. The RG possesses a robust molarlike pharyngeal apparatus which is adapted to processing hard-bodied prey. In contrast, the pharyngeal apparatus of the TG has not been described. Lower pharyngeals were removed from 15 length-matched (31-48mm total length, TL) RG and TG, fixed, cleared, stained, and photographed. Several linear and areal measurements were made, and geometric morphometric analysis on pharyngeal outlines was conducted to determine if pharyngeal morphology differed between species and changed with body length within each species. Results of our analysis of pharyngeal morphology demonstrate: 1) left and right elements fuse in round goby but remain separate in tubenose goby, 2) total area and toothed area is greater in RG and increase at faster rates with TL in RG, 3) pharyngeals of both species change shape with increased TL through the addition of bone medially and posteriorly, but RG deposit bone at a greater rate, 4) pharyngeals of RG contain many large-diameter teeth (especially near the posterior margin), whereas pharyngeals of TG contain fine, recurved teeth. Our results suggest that dietary differences between RG and TG are due to differences in pharyngeal morphology in which TG do not have a pharyngeal apparatus well-suited to processing mollusk prey.