Tolerance of Theora fragilis (Bivalvia: Semelidae) to Low Concentrations of Dissolved Oxygen

Abstract

In Japan, the semelid small bivalve Theora fragilis is common in muddy bottoms of eutrophic semi-enclosed bays where oxygen-deficiency occurs in summer. However, its tolerance to low concentrations of dissolved oxygen (DO) has not been studied. In the present study, the tolerance and behavior of Ts fragilis in low DO concentration were examined in laboratory experiments. In anoxic conditions, the bivalves survived for 2 days at 15°C or 1 day at 25°C. In severe hypoxia (DO concentration: 1.3-1.4mg/l), almost all individuals survived for at least 4 days without irreversible physiological injury, though feeding activities were reduced. The behavior and survivorship under moderate hypoxia (DO concentration: 2.2-2.4 mg/l) were similar to those under normal air saturation; feeding was very active and all individuals survived throughout the experiment. These results imply that T. fragilis has a fairly high tolerance to low DO concentrations. It was discussed that such a fairly high tolerance might be useful for the survival and prosperity of T. fragilis populations. © 1993, The Japanese Society of Fisheries Science. All rights reserved.