Variation in Meristic Characters of Head Seismosensory System in Roach Rutilus rutilus (L.) under Hydrochemical Conditions of Water Bodies of Udmurtia

Average and summary values of five paired meristic characters of the head seismosensory system have been estimated in roach from 11 ponds and medium-size reservoirs in Udmurtia. It has been found that the level of fluctuation variance in the summary character values is significantly correlated with the values of water mineralization and total dry solids in the water bodies, and the average summary values, with the absolute and relative contents of magnesium ions in the water. A possible role of magnesium in determining the quantitative indices of seismosensory characters, which are formed during early fish ontogeny, is discussed with regard to the results of a pilot laboratory experiment on rearing roach juveniles under different hydrochemical conditions.