Combined impact of toxicants and helminths on great pond snail (Lymnaea stagnalis L.) homeostasis stability

Abstract

Anthropogenic pressure on the hydrosphere has led to the progressive increase in its pollution by various components of both industrial and domestic effluents. The surfactants, which are the components of synthetic detergents, are among the most dangerous for aquatic organisms. The effect of different concentrations of detergent “Ushastyi nian” produced by “Vinnytsiapobutkhim” was studied in concentrations of 2.5, 5, 10, 20, 40 mg/dm3 on a number of physic-chemical parameters of the homeostasis of haemolymph of Lymnaea stagnalis (Linnaeus, 1758). The investigated great pond snails were intact or infected with various life cycle stages (maternal and daughter redia, cercariae) of the trematode Echinoparyphium aconiatum Dietz, 1909. The studied material includes 315 individuals of mollusсs collected by hand in the reservoirs of the drainage and reclamation system in the basin of the Teteriv River (right-bank tributary of the Middle Dnieper river) in Central Polissya (Zatyshshia village, Zhytomyr Region). The toxicological experiment was conducted by standard scheme according to (Alekseev, 1981). It was preceded by a mandatory (Khlebovich, 1981) 15-day acclimation of animals intended for toxicological examination to aquarium conditions (volume of aquaria 20 l, density of molluscs 3–4 individuals/l, water temperature 20–22 °C, pH 7.9–8.4, oxygenation 8.1 to 8.5 mg O2/dm3). The presence of molluscs in toxic environments was accompanied by the development of a responsive reaction such as poisoning. The most obvious symptoms were quantitative changes in the values of physic-chemical parameters of their haemolymph, which largely ensure its homeostasis. These parameters include the total protein level, the specific gravity, and pH. In these molluscs, about 90 % of the total haemolymph protein is represen­ted by haemocyanin. It determines, due to its powerful buffering properties, both the level of oxygen capacity and water-osmotic pressure in the body of molluscs. The pathological process, which develops as a result of combined toxicant and helminthic invasion impact on L. stagnalis expresses more clear, quick and higher toxicant concentration, helminthic invasion intensity and durability level of different lifecycle stages of trematodes. The experimental molluscs defend themselves against the affected values of the mentioned indicators of stability of homeostasis by the set of inherent protective and adaptive reactions (rapid behavioral, physiological and biochemical ones). They aimed at maintaining the viability of individuals. The effectiveness of protective and adaptive reactions in trematode-infected molluscs was significantly lower compared to non-infected individuals. The degree of cumulative damaging effect of the toxicant and parasites was determined not only by the concentration of surfactants. To a large extent it depended on both the rate of the infection and the stage of the life cycle of parasites. The pathogenic effect of the latter on their mollusc hosts decreased as follows: “old” (maternal) redia > “young” (daughter) redia > cercariae.