The Effect of Acute Hypoxia and Hydrogen Sulfide Contamination on Succinate Dehydrogenase Activity and the Adenylate Complex in Tissues in the Bivalve Mollusk Anadara kagoshimensis (Tokunaga, 1906)

The separate effects of acute hypoxia and hydrogen sulfide load on the succinate dehydrogenase (SDH) marker enzyme of the mitochondrial respiratory chain and the adenylate status of tissues in the bivalve mollusk Anadara kagoshimensis (Tokunaga, 1906), which is a species tolerant to these groups of factors, were studied under experimental conditions. The study was carried out on adult individuals with a shell height of 23–34 cm. The control group of bivalves was kept in water with an oxygen concentration of 7.0–8.2 mg О₂/L. One experimental group was exposed to acute hypoxia (0.1 mg О₂/L) and the other to a hydrogen sulfide load (6 mg S^2–/L). The exposure period in both cases was 48 h. The water temperature was maintained at 17–20°C. Acute hypoxia led to an increase in the SDH activity in all the studied tissues (gills, foot, and hepatopancreas). This reaction was not observed under the hydrogen sulfide load. The energy state of the tissues decreased in both cases. This was expressed as a decrease in the ATP and ADP contents accompanied by an increase in the AMP content, which allows the adenylate kinase reaction. These changes were more pronounced in the presence of hydrogen sulfide. However, the adenylate pool and adenylate energy charge (AEC) remained at a relatively high level, which indicates the ability of the ark clam to exist in the near-bottom water layers with a low level of oxygen and the presence of hydrogen sulfide. It is assumed that mitochondria of the ark clam have an alternative oxidase that is not sensitive to the presence of sulfides in water.