Metabolic characterization of Diplodon chilensis (Gray, 1828) (Bivalvia: Hyriidae) exposed to experimental anoxia.

Diplodon chilensis is a freshwater bivalve inhabiting from northern Chile to Tierra del Fuego. This species has a high filtration capacity and great tolerance to hypoxic environments. Thus, the aim of this study was to characterize,  for the first time, anaerobic metabolism of D. chilensis using an enzymatic approach by measuring piruvate oxidoreductases and malate dehydrogenase activities in two groups of organisms. A first group (G1) corresponded to organisms analyzed immediately after their collection from Lleu-Lleu Lake (36ºS). The second group (G2) corresponded to organisms analyzed after exposition to extreme anoxic conditions in laboratory. Enzymatic activities were measured in abductor muscle, foot, gills, hepatopancreas gland, and mantle-gonad tissue. Positive activities were detected for piruvate oxidoreductases (PORs: lactate dehydrogenase (LDH), octopine dehydrogenase (OPDH), strombine dehydrogenase (STRDH), alanopine dehydrogenase (ALPDH)) and malate dehydrogenase (MDH). MDH showed the highest dehydrogenase activity observed in all tissue and groups analyzed. Nevertheless, only those organisms exposed to extreme anoxic conditions showed significant relationships between MDH and LDH activities and a high ratio of (MDH/LDH) between them. All these enzymatic features of D. chilensis correspond to a species with a successfully anaerobic metabolism to cope with extreme anaerobic conditions.