Body Shape Variability of the Minnow Phoxinus phoxinus (Linnaeus, 1758) (Cyprinidae, Actinopterygii) in Large and Small Watercourses of the Sylva River Basin (the Middle Urals)

The body shape variability of minnow populations in different-size watercourses in the Sylva River basin (the Middle Urals) was investigated by geometric morphometrics. 26 homologous landmarks were used to describe the body shape variability of fish. Four geographically adjacent minnow populations isolated by artificial and natural dams were studied. More than 56% of the variance of inter-group morphological differences in minnows is due to the minnow inhabiting the large watercourse of the main stem (the Sylva River) and its small tributaries (the Lomovka River, the Musorka River, and the Sarga River). The main-stem minnows are distinguished by relatively large eye size, low body, and small short jaws. The tributary minnows are characterized, on the contrary, by relatively high body, small eyes, and long jaws. Along with the revealed significant differentiation of the isolated minnow populations from the main stem and its tributaries, a high level of individual morphological differences was discovered, which indicates some directed change of the fish development trajectory in the population from each stream. The discrimination level of individuals reached 97.9%. A low intra-group diversity of body shape was identified for the minnow population in the large watercourse of the Sylva River with its multi-species ichthyologic diversity. The minnows from the small watercourses of the Lomovka, Musorka and Sarga rivers with their low specific diversity have an increased intra-group body shape diversity. It may indirectly indicate some ontogeny change in the individuals from the small tributaries, related to the formation of a wide range of ontogenetic trajectories and suggests a high phenotypic plasticity of the species. The role of the hydrological regime in small watercourses and the taxonomic diversity of fish communities in the formation of the minnow morphological diversity is hypothesized.

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