Response of juvenile Lophiosilurus alexandri to osmotic and thermic shock.

Abstract

The objective of the present study was to evaluate the physiological responses of juvenile Lophiosilurus alexandri submitted to osmotic and thermic shock. Thirty juveniles were used for each test, of which 10 were not subjected to stress and remained in normal conditions (fresh water at 28.0°C). The others were submitted to stress shock (saline water of 10.0g of salt/L or water cooled to 18.0°C). Blood samples were taken at 0h (no exposure to the stress factor) and 1h and 24h after the tests. At 24h, the survivorship was 100% in both tests. In both the osmotic and thermic shock tests, cortisol and glucose levels were higher at 1h but then decreased after 24h. Lactate dehydrogenase showed differences in the temperature test, but there was no difference between 1 and 24h after exposure to osmotic shock (P > 0.05). The difference was recorded in blood gas variables (pH, PvCO2, PvO2, hemoglobin, sO2, BE, tCO2, HCO3-, and stHCO3-) and electrolytes (Na+, Ca++, nCa++, and K+) in both experiments. With regard to hematology and blood biochemistry, exposure to thermal shock did not affect (P > 0.05) ALP, total plasma protein, hematocrit, and ALT and AST at 1h and 24h. ALP and total protein in the blood of fish submitted to the osmotic shock were lowest (P < 0.05) at 24h. Leukocyte and erythrocyte counts exhibited differences after osmotic shock, in contrast to erythrocyte counts of the temperature test, which did not change in 24h (P > 0.05). Juveniles of L. alexandri were able to reestablish the main indicators of stress (cortisol, glucose), while the others (hematological, biochemical, and gasometric) varied in compensation for normal physiological reestablishment.