Hematological changes in jundia (Rhamdia quelen Quoy and Gaimard Pimelodidae) after acute and chronic stress caused by usual aquacultural management, with emphasis on immunosuppressive effects

Blood samples of 1-year-old male jundia (Rhamdia quelen, Quoy and Gaimard) were collected to determine the effects of both acute and chronic stress in hematological parameters. The acute stress was induced by draining the water tank and transferring fish to another tank; chronic stress was induced by maintaining the fish in crowded concrete tanks. The cortisol level of male fish, 1 h after transferring from one tank to another, reached 176.78 +/- 21.3 ng/ml in contrast to 28.89 +/- 5.19 ng/ml found before transferring. Chronic stress, induced by 10 days of crowding in concrete tank, maintained the cortisol levels in approximately 64.48 +/- 18.9 ng/ml. The haematological parameters evaluated (RBC, WBC, and haemoglobin) were not significantly affected by acute stressor. However, after 10 days of chronic stimulation, all these values changed, with a significant decrease in lymphocytes, eosinophils, monocytes and special granulocyte cells, as well in RBC and hematocrit. The main result found in this work was the reduction of approximately 80% in the lymphocyte counts. This reduction could lead to a decreased ability to mount an immune response to environmental pathogen and could be an indication that the correct management of brood and culture stocks is important to prevent stress and the deleterious effects of increased cortisol levels to fish health. (C) 2004 Elsevier B.V. All rights reserved.