Swimming performance and physiological responses of juvenile Cojinoba Seriolella violacea in hypoxic conditions

Abstract

Understanding environmental constraints and associated physiological adaptations of culture organisms is key for the implementation of off-shore grow-out facilities. In the southeast Pacific Ocean along the coasts of Chile and Peru, seasonal upwelling events lead to hypoxic conditions, which are projected to increase in both frequency and intensity with climate change. Aquaculture operations must take into account the physiological adaptability of a species for environmental conditions. For Cojinoba (Seriolella violacea), a native target species for aquaculture diversification in northern Chile, little is known in regard to physiological capacity for hypoxia. Therefore, hypoxia tolerance studies were conducted followed by measurement of resting and active metabolism and associated energy facilitation in response to hypoxia in juvenile Cojinoba. Hypoxia tolerance studies found they were resilient to dissolved oxygen levels of 1.0 mg O2 Lˉ1 for 8 h. Swimming metabolism studies exposed Cojinoba to normoxia (7.5 mg O2 Lˉ1) or hypoxia (1.0 mg O2 Lˉ1), and quantified minimum metabolic rate (MO2 min), active metabolic rate (MO₂ max), critical swimming speed (Ucrit) and associated energetic metabolites and hematological variables. In hypoxia, there was a decrease in MO₂ max (34%) leading to a large (82%) decrease in aerobic metabolic scope. MO2 min decreased as well by 12%, with lactate increasing presumably to temporarily maintain basic metabolic function. In addition, Ucrit decreased by 53% in hypoxia, although tail beat frequency was similar in normoxia and hypoxia up to a velocity of 40 cm s−1. Moreover, although erythrocyte concentration increased in hypoxia, hemolysis was observed in exercised fish in this condition. There was a notable increase (5-fold compared to normoxia) in lactate levels of exercised fish in the hypoxia group, which suggests a quick conversion to anaerobic metabolic pathways to maintain energy balance when swimming in hypoxic environments. Therefore, Cojinoba have adaptive responses that may facilitate survival during severe hypoxic events although overall physiological performance is diminished.