Spotless round gobies: A poorly described phenotype of Neogobius melanostomus

Abstract

The round goby (Neogobius melanostomus) is a widely distributed invasive fish, typically distinguished from morphologically similar native species by a prominent black spot on the first dorsal fin. Although spotless individuals have been reported, their prevalence and characteristics remain poorly documented. Spotless round gobies were discovered in the St. Lawrence and Richelieu rivers in Quebec, Canada. Mitochondrial DNA analysis confirmed their identity as N. melanostomus, indicating that the spotless form represents a phenotypic variant within the species. In both rivers, the frequency of this phenotype was found to be low, ranging from 0.18 to 1.14%, with no apparent association with sex and body length. To contextualize these findings, a literature review on this phenotype and its occurrence is presented. The existence of spotless round gobies may challenge public awareness and monitoring efforts, particularly those that rely on the presence of the typical dorsal spot for accurate species identification.