ФЛУКТУИРУЮЩАЯ АСИММЕТРИЯ СЕЙСМОСЕНСОРНЫХ КАНАЛОВ ГОЛОВЫ У ВЕРХОВКИ LEUCASPIUS DELINEATUS (HECKEL, 1843) ИЗ МАЛЫХ ПРУДОВ С РАЗНЫМИ ВЕЛИЧИНАМИ МИНЕРАЛИЗАЦИИ ВОДЫ И СОДЕРЖАНИЯ КАТИОНОВ ЖЕСТКОСТИ

Abstract

Background. The change in external conditions is accompanied by various responses of organisms existing in an unstable and heterogeneous environment. Relevance. Under the influence of physico-chemical factors of the aquatic environment, the frequency and extent of asymmetric manifestations of bilateral morphological features in fish individuals may increase, which is a consequence of an imbalance in their development and reflects the level of environmental stress. The aim of this work was to examine the fluctuating asymmetry (FA) in the number of pores in the head seismosensory canals of belica Leucaspius delineatus (sunbleak) from the water bodies that differ in the content of total dissolved solids (water mineralization) and hardness cations. Methods. Ichthyological material was collected in nine small ponds belonging to the Kama River basin in the Udmurt Republic in 2018-2019. In the captured individuals of belica, the number of pores in the seismosensory canals in four paired head dermal bones has been identified, on the basis of which two FA indices have been calculated. Results. In several water bodies, a considerable proportion of belica mature individuals with incompletely ossified sections of the head seismosensory canals, often on one side only, or on the both sides but to different extents, has been recorded. This proportion determined the FA indices of the studied seismosensory features and had a positive correlation with the content of magnesium ions in the water bodies. In the belica individuals with fully ossified head seismosensory canals, the FA variance of the total number of pores in these canals had a positive correlation with the total dissolved solids in the water of the investigated small ponds; however, it had not depended on the content of hardness cations in them. Conclusion. The possible mechanisms of the influence of the investigated hydrochemical factors on the morphogenetic processes sequentially occurring in the belica early development - anlage of the raws of primary head neuromasts in its larvae and the subsequent formation of the ossified sections of the head seismosensory canals in its fry - are discussed.