The variability of external morphology characters (36 morfometric and 6 meristic) of the round goby Neogobius melanostomus (Pallas, 1814) from 7 regions of the Azov-Black Sea basin is considered: the northwestern and southwestern Black Sea coasts of the Crimean Peninsula (Karkinitsky Gulf, Donuzlav Lyman, Streletskaya Bay of Sevastopol), the Kazantip Bay of the Sea of Azov, as well as the Salgir River in the central part of the Crimean Peninsula. It was established the round goby from different areas of catch at the age of 2+-3 has different body sizes – the largest in individuals from Streletskaya Bay (SLav=136.2±1.97 mm), the smallest from the Salgir River (SLav=66.8 ±2.28 mm). Using the Mann-Whitney test, statistically significant differences were established between the samples for most morfometric characters. According to meristic characters, they are absent. The greatest contribution to the discrimination of round goby samples is made by morfometric characters associated with the location of the fins. According to the results of cluster analysis, according to the totality of all the studied traits, in the round goby of the Azov-Black Sea basin, the samples from Karkinitsky Gulf (Samarchik Bay and Yarylgachskaya Bay (D = 28.6)) have the greatest similarity, they are joined by a sample from the water area of the Bakalskaya Spit. At the level of divergence D=47.3, groups of gobies from Streletskaya Bay and Kazantip Bay are united, and then a sample from the Donuzlav Lyman adjoins them at the level D=215. The sample of the goby from the Salgir River occupies the most isolated position – the level of divergence was about 475. According to the discriminant analysis, it was found that the round goby from the Azov-Black Sea basin is differentiated into at least three spatial groups: one from the area of he western coast of the Crimean Peninsula (Karkinitsky Gulf and Donuzlav Lyman) and the area of Sevastopol (Streletskaya bay); the second – from the Kazantip Bay (Sea of Azov) and the third – from the Salgir River. The following measurements made the greatest contribution to the discrimination of spatial groupings (when the correlation coefficient between features and coordinate values along the second canonical axis is greater than 0.75): maximum body depth, caudal peduncle depth and width, predorsal and prepelvic distances, and width of pectoral and pelvic fin base. The revealed heterogeneity shows a high paratypical variability of morfometric characters and that under different environmental conditions, individuals of the same species form a specific phenotype.