Erythrocyte nuclear abnormalities and leukocyte profile in the Antarctic fish Notothenia coriiceps after exposure to short- and long-term heat stress

Several studies suggest that Antarctic endemic stenothermic fish species, such as Notothenia coriiceps, have a limited ability to acclimate to warmer conditions. In the present study, we evaluated the effects of exposure to short- and long-term temperature increases on the occurrence of erythrocytic nuclear abnormalities (ENAs) and changes in the leukocyte profile of N. coriiceps. For the experiments, 30 specimens of N. coriiceps were captured in Admiralty Bay and transferred to the Commandant Ferraz Brazilian Antarctic Station where they were acclimated to water at 0 °C for 6 days and subsequently subjected to treatments of temperature increases (2–4 °C) on a short- (1 day) or long- (6 days) term basis. At the end of exposure, peripheral blood samples were collected and blood smears were prepared for qualitative and quantitative analysis of the ENAs and the leukocyte profile. Significant responses were observed for both ENAs and leukocyte profile. The responses of ENAs were characterized by an increased incidence of bilobed nuclei in erythroblasts following 1-day exposure to water at 2–4 °C, as well as increased incidence of bilobed nuclei in erythrocytes following 1-day and 6-day exposure to water at 4 °C. In the leukocyte profile, 1-day exposure to water at 2 °C promoted a stress response characterized by diminished levels of circulating lymphocytes (lymphopenia) and elevated levels of circulating monocytes (monocytosis). In conclusion, our results indicate that elevation of water temperature during short periods provoked cellular and physiological stress in N. coriiceps. Furthermore, we conclude that in terms of nuclear alterations, erythrocytes and erythroblasts respond differently to thermal stress. Finally, we conclude that the methodology proposed was efficient in quantifying thermal stress in N. coriiceps and we recommend the utilization of this technique in the biomonitoring of thermal stress in this species and other notothenioids.