Chronic impact of exposure to low dissolved oxygen on the physiology of Dicentrarchus labrax and Sparus aurata and its effects on the acute stress response

Abstract

Dissolved oxygen (DO) saturation in the water is a crucial factor in fish performance and welfare. Exposure to low DO can affect a wide variety of functions such as metabolic rate and physiological adaptations including hematological, hormonal, biochemical and osmoregulatory alterations in blood and plasma. In the present study European sea bass, Dicentrarchus labrax and gilthead seabream, Sparus aurata were reared for approximately 3 months at different levels of DO saturation, namely 40–60%, 60–80% and 80–100% at a temperature of 26.5 °C. Both species showed reduced performance at the lowest DO regime compared to the highest, as well as a reduced aerobic capacity as indicated by the aerobic scope and the post-stress lactate concentrations. Blood samples were collected before and after exposure to an acute chasing and confinement stress. Hematocrit, hemoglobin and mean corpuscular hemoglobin concentration were affected by DO saturation in Dicentrarchus. labrax but not in parus aurata. Cortisol levels in fish plasma and scales were similar between different DO regimes in both species, while in plasma it was increased after exposure to acute stress. Moreover, in both species post-stress levels of osmolality and lactate were higher at the lowest DO examined, indicative of osmoregulatory imbalance. Based on multivariate analysis glucose and lactate were highly affected by acute stress in low oxygen saturation in D. labrax, while osmolality was mostly affected in S. aurata. Overall, this study provided a detailed insight in the effects of DO in the physiology of D. labrax and S. aurata.