Fish Carboxyl Esterase Activity as a Possible Hypoxia Biomarker

Abstract

Physiology and biochemistry adaptations studied in fish are important to comprehend how they endure the challenges of living in aquatic environments. Oxygen variations are a frequent natural and cyclic phenomenon that occurs in the Pantanal and Amazon watersheds and it is the limiting factor to survival of the aerobic species. The growing of pollution in these water basins threaten many species as anthropic hypoxia intensifies the production of reactive oxygen species (ROS) and lipid peroxidation inside the cells, leading organisms to a condition known as oxidative stress. Our research group, studying the effects of the oxygen variations on the carboxyl esterase (CarbE) enzyme of pacu, a typical fish from Pantanal, observed that CarbE activity diminished by half in pacus exposed to 42 hours of hypoxia. Based on this finding, we decided to investigate this phenomenon in other fish species, including hypoxia-tolerant fishes. CarbE activities were determined using p-nitrophenyl acetate (p-NPA) as a substrate. All five species of fish studied had both serum and liver CarbE activity significantly decreased. Pacus had its serum and liver activities decreased by approximately 50% under severe hypoxia.