Effect of acute crowding stress on subsequent osmotic challenge and recovery in juvenile common carp Cyprinus carpio (Linnaeus)

Abstract

Effect of acute crowding stress (density of 25 g/L for 2 and 4 h) on subsequent salinity (8 g/L) tolerance was investigated in juvenile common carp (Cyprinus carpio). To assess osmoregulatory conditions, blood cortisol, glucose, Na+ and Cl− concentrations were measured at 0, 6, 24 and 72 h after osmotic challenge in three groups: control, and groups stressed for 2 and 4 h. Results indicated typical stress responses after crowding stress. In both stressed groups, cortisol was significantly higher than the control group, but no significant difference was observed within the stressed groups. Additionally, glucose levels increased after crowding stress, and there was a significant increase in the in 4-h group compared with the 2-h group. Ion concentration was not significantly affected by crowding stress. Osmotic challenge led to an increase in cortisol and glucose concentrations in unstressed fish, after 6 h, but in stressed fish, no change occurred in cortisol and glucose levels at this point compared to the pre-challenge values. There was no significant change in cortisol and glucose values at 6, 24 and 72 h after the osmotic challenge between groups. Cortisol and glucose returned to pre-stress values by 72 h following the challenge. In all groups, Na+ concentration significantly increased at 6 h after the osmotic challenge and stayed elevated until 72 h; however, there was no significant difference between groups at any time point. There was no significant difference in Cl− concentrations between groups or sampling time points. These results indicate that the common carp is a hyperosmotic regulator after exposure to saline medium, and acute crowding stress does not impair osmotic stress response.