Ontogenetic variability in external morphology of bighead goby Neogobius kessleri from the Middle Danube, Slovakia

Over the last decade, four species of goby have invaded the Middle Danube area, and all of them have spread rapidly. In the early 1990s, bighead goby Neogobius kessleri appeared in the Middle Danube, where it now seems to thrive. Relatively little is known of the environmental biology and ontogeny of this species in its native and non‐native ranges. In this paper, preliminary results on the external morphology of bighead goby from the Slovak stretch of the Danube are presented within an ontogenetic context. Patterns of relative growth with no apparent changes at small size suggest direct development in bighead goby, although not as profoundly direct as observed in round goby N. melanostomus. Differences in life history between these two closely related species may have important implications for their success in novel environments, favouring the latter in short term (several years) and the former in long term (decades and longer) perspective.