Variation in external morphology between the native and invasive populations of the round goby, Neogobius melanostomus (Actinopterygii: Gobiidae).
Fish established outside their native range often express various changes in external morphology, which may result in significant variation between individuals inhabiting different regions. In the current study we aim to explore differences in morphology among several populations of the round goby (Neogobius melanostomus), an invasive fish in Europe and North America. A total of 753 round gobies were collected from several invasive and native populations, including marine, brackish, freshwater, lake and river ecosystems belonging to the Black Sea, Baltic Sea and Great Lakes watersheds. We analysed 35 metric and meristic characters using ANOVA, discriminant analysis and allometric coefficients. Our results indicate significant differences between most of the populations in characters such as inter orbital distance, eye diameter, head width, second dorsal fin length and depth. River dwelling round gobies had elongated ventral fins compared to those from standing water bodies-a possible adaptation for upstream dispersal in flowing habitats. Most of the morphologic characters expressed positive allometry with significant differences in allometric coefficients between populations. Probably due to their recent invasive history, some of the head characters and allometric models grouped together round gobies from the Great Lakes watershed with those from a newly established population in the Danube tributaries. Similarities between geographically distant round goby populations might reflect common adaptations in external morphology during the course of invasion.