Compound effect of nitrates and biotic factors on the in vitro activity of epithelial cilia of outer demibranchs of Sinanodonta woodiana (Mollusca, Bivalvia, Unionidae)

Abstract

Effects of MPC, 2 MPC, and 3MPC water solutions of potassium nitrate and biotic factors (trematode infection and “gill pregnancy”) were studied on the duration of locomotion and beat frequency of epithelial cilia of outer demibranchs of Sinanodonta woodiаna (Lea, 1834). The species has recently invaded the system of water bodies of Ukraine. It has occupied numerous water bodies in the Kiliya distributary of Danube Delta, establishing populations of density and biomass. Statistically significant differences by the studied parameters of ciliary epithelium (duration of locomotion and beat frequency of cilia) were not observed in the control group of non-infected males and latent females of S. woodiana. In females with “gill pregnancy”, the duration of ciliary locomotion decreased by 1.5 times, and beat frequency by 1.4 times (P>99.9 %). It should be noted that the outer surface of demibranchs of female mollusks was completely covered by the filled to the brim marsupial pockets. Thus, the functional load of gills is high, leading to the development of compensatory processes in experimental animals. The processes induce increased effectiveness of protective factors that counteract them. Another biotic factor negatively affecting the experimental pond mussels was the high rates of trematode infection in the hosts’ reproductive glands which contained sporocysts and cercariae of Rhipidocotyle campanula Dujardin, 1845. Prevalence of that infection ranged from 50 to 100 %. These rates of infection were associated with sharply declining functions of cilia of the gill epithelium in studied animals. The compound pathogenic influence of parasite and “gill pregnancy” factors even more affected the functional parameters of outer gill ciliary epithelium. The MPC levels of toxicant in the water medium were accompanied with the first symptom of intoxication of the Chinese pond mussel, the stage of stimulation. At that point, the functional parameters of epithelial cilia of “pregnant” females and in moderately and weakly infected mollusks of both sexes increased in response to exposure to the toxic factor. With the growing concentrations of toxicant to 2 MPC and 3 MPC, the experimental pond mussels developed the pathological process of intoxication, which progressed from the stage of depression to sublethal and lethal stages. Accordingly, the locomotion activity of ciliary epithelium increasingly declined and, in the end, stopped. The “gill pregnancy” and high rates of trematode infection exacerbated the consequences of the process.