Spatial morphometric plasticity of spirlin Alburnoides bipunctatus (Bloch, 1782) phenotype from the Nišava River, Serbia, Danube basin

Variation of 22 morphometric and 4 meristic characters of the species Alburnoides bipuuctatus from NišavaRiver were analyzed. Specimens were collected from four sampling stations along the putative mesohabitatgradient of river influence and were grouped into the categories with similar total length. Morphometric charactersvaried immensely between different mesohabitats outlining morphometric plasticity. Among severalmorphometry features that were influenced by different mesohabitats the most observable differences werenoted for: postocular distance, anal fin height, minimal body height and preanal length. Regarding themeristic features, number of soft rays in the anal fin did varied significantly among sampling stations while fourthhard ray in the anal fin for this species was reported for the first time ever. Pharyngeal teeth formula of spirlin alsoshowed variability across different mesohabitats. In conclusion, it appears that spirlin express a bigmorphological plasticity in relation to spatial and mesohabitat distribution and there is a possibility that spirlin fromNišava River is a complex of neospecies in formation/morphotypes/ecotypes rather than a single population