Morphological Characteristics of the Nonindigenous Brown Bullhead Ameiurus nebulosus (Le Sueur, 1819) in Lakes of the Karelian Isthmus (Northwestern Europe)

Abstract

Nonindigenous brown bullheads from two lakes of the Karelian Isthmus have been studied in relation to 36 morphological features characterizing the shape of the body and head, the position of the fins, and the number of finrays and vertebrae. The results are compared with data for the collection materials and data published earlier for other parts of the species distribution range in order to assess the intraspecific differentiation and morphological plasticity of this invasive species. Meristic characters of individuals from geographically distant sites are quite similar, and no difference between areas have been found. On the contrary, significant differences in morphometric characters between samples from geographically remote areas of Europe are shown, reaching the thresholds established for subspecies identification. The high level of morphometric variability in the invasive brown bullhead indicates a high phenotypic plasticity in external morphological traits responsible for fish locomotion, which is considered among factors contributing to its successful adaptation to new habitats and determining the invasive potential of this species.