Fluctuating Asymmetry of the Traits of the Seismosensory System of the Roach Rutilus rutilus (L.) (Cyprinidae, Pisces) and the European Perch Perca fluviatilis L. (Percidae, Pisces) in Small Ponds with Various Water Mineralization

The number of pores in the seismosensory canals of several paired integumentary head bones was counted for specimens of the roach and European perch caught in 15 small ponds in the central-eastern part of the Udmurt Republic, Russia. Three indices of fluctuating asymmetry were calculated on the dataset obtained, and a statistical analysis of the relationships of these indicators with the average (over several years) mineralization of water bodies for different periods of the growing season and with their variation coefficients has been carried out. In the roach, the average proportion of asymmetric variants of the studied traits was significantly associated with seasonal variability of mineralization values only, while close and statistically significant relationships between this indicator and the average mineralization values in individual periods of the growing season have been found in the European perch. Similarly, another indicator of the roach, the variance of fluctuating asymmetries of the total values of paired meristic signs of the cranial seismosensory system, was similarly associated with these values. Possible mechanisms of the influence of the mineralization factor on the degree of asymmetric manifestation of the studied signs are discussed, taking into account the features of their gradual formation in the early ontogenesis of the two fish species. As a result, some limitations on the adequate use of these indicators in the bioindication of anthropogenic pollution of freshwater by dissolved inorganic substances are considered.