Molecular responses to hypoxia in Atlantic salmon (Salmo salar)

Hypoxia is a common event in aquatic environment, and it is developed when the consumption of oxygen by organisms in an aquatic system exceeds the supply of oxygen from adjacent layers of water or the atmosphere. Fish react to hypoxic condition by behavioral, physiological, and cellular responses to maintain the function in an oxygen-depleted environment. In this project, we investigated the expression of several fundamental genes involved in the adaptation of Atlantic salmon (Salmo salar) to hypoxic condition. Two groups of juvenile fish raised at chronic normoxic and hypoxic conditions during early development were subjected to acute hypoxia (30% dissolved oxygen) or normoxia for 48 hours. Tissue samples from liver and muscle were assessed to monitor expression levels of genes producing enzymes involved in hypoxia adaptation mechanisms (HIF-1α), glucose and lactate metabolisms (LDH-α, MDH, PK and PKM) and antioxidant defense (CAT and SOD). LDH enzymatic activity in the liver and the muscle together with liver glycogen content were measured to investigate metabolic kinetics. The results demonstrated that exposure of juvenile Atlantic salmon to acute hypoxia caused changes in expression level of genes involved in metabolic pathway, antioxidant defense and hypoxia adaptation. Also, this study indicates that fish experiencing hypoxia in hatchery, start feeding, and during fingerling period display different gene expression patterns after exposure to acute hypoxia, compared to fish raised in normoxic condition.