Adaptation of Anadara kagoshimensis (Tokunaga, 1906) to Hypo- and Hyperosmotic Environment: Hemocyte Response

Abstract

Anadara kagoshimensis (Tokunaga, 1906) is an alien bivalve mollusk that has successfully colonized the Black Sea and the Sea of Azov despite a significantly lower salinity level of these waters compared to its native region. The morphological and morphometric characteristics of erythrocytes from A. kagoshimensis during adaptation to hypo- and hyperosmotic experimental conditions were analyzed by light microscopy. The control group of mollusks was maintained at 18‰ salinity. Experimental groups were maintained at the salinity levels of 8, 14, 35, and 45‰. A decreased salinity level was obtained by diluting seawater with distilled water at a rate of 1.5 ± 0.5‰ per day. An increased salinity was obtained by addition of sea salt to an aquarium at a rate of 2.5 ± 0.5‰ per day. The exposure period was 2 days. The natural salinity range of A. kagoshimensis was found to fall within 14—35‰. No significant cell morphology changes were observed under such conditions. At the same time, exposure of the mollusks to the environmental salinity of 8 and 45‰ caused an obvious stress expressed via appearance of cell anomalies and changes in the linear characteristics of erythrocytes. At the same time, no cell lysis was observed, and the values of the specific surface area and the nuclear-cytoplasmic ratio remained unchanged. The results of the study indicate the ability of the mollusk to survive for some time in an aquatic environment with extremely low or high salinity.