Respostas fisiológicas de Lophiosilurus alexandri a diferentes situações de estresse: teste de exposição ao ar, choque térmico e choque osmótico

Abstract

The aim of this study was to evaluate the physiological responses to stress in Lophiosilurus alexandri juveniles submitted to air exposure tests, osmotic and thermal shock. 72 juveniles weighing 361.06 ± 42.82 g were used for the air exposure test. Twelve juveniles were not submitted to the test and 60 were submitted to the air exposure test for 30 minutes. Blood samples were taken at 0 h: no air exposure; time 0.5 h: animals shortly after air exposure for 30 min (before returning to the tank); time 1.5 (90 minutes), 24, 48 and 96 hours after air exposure. 30 juveniles were used for the saline and thermal shock tests each. Ten juveniles were not submitted to the test, remaining in normal environmental conditions (freshwater water and water at 28° C, respectively). The remaining 20 animals from each test were submitted to stress shock by two different tests (saline water at 10.0 g salt / L and water cooled at 18.0° C). Blood samples were taken at 0 h: no exposure to the stressor factor; 1 hour and 24 hours after the tests. In the air exposure test, after 96 h survival rate was 100%. Cortisol and glucose were higher at 0.5 h, returning to baseline values at 48 and 24 h. In the osmotic and thermal shock tests, at 24 h the survival rate was of 100% in both tests. In the osmotic and thermal shock tests, cortisol and glucose were higher at 1 h, dropping concentrations at 24 h, respectively. Lactate dehydrogenase showed no difference in the temperature test, but indicated lower concentrations at 1 and 24 h. In the air exposure test, lactate dehydrogenase presented higher values at 1.5 h after exposure to air, returning to normal values in 24 h. Regarding hematology and blood biochemistry, air exposure did not affect (P> 0.05) globular volume and aspartate aminotransferase over 96 h. Alkaline phosphatase had the highest (P <0.05) values at 0, 1.5 and 24 h. Total protein was similar between 0 and 1.5 h (P> 0.05) and the lowest values at 96 h. Alanine aminotransferase was greater at 0.5 h. Leukocyte was higher at 0.5, 1.5, 48 and 96 h. Erythrocyte presented higher values in 96 h (P> 0.05). Considering hematology and blood biochemistry, exposure to thermal shock did not affect (P> 0.05) alkaline phosphatase, total plasma protein, hematocrit, ALT and AST at 1 and 24 h. Alkaline phosphatase and total protein from osmotic shock showed lower (P <0.05) values at 24h. Leukocyte and erythrocyte after the osmotic shock showed differences from the posttest times, different from the erythrocyte from temperature test, which did not change in 24 h (P> 0.05). Several changes were recorded in the blood gas variables (pH, PvCO2, PvO2, hemoglobin, sO2, BE tCO2, HCO3- and stHCO3-) and electrolytes (Na+, Ca++, nCa++ and K+) post stresses. Juveniles of L. alexandri were able to reestablish the main indicators of stress (cortisol, glucose), while the others (hematological, biochemical and gasometric) presented compensatory variations for normal physiological reestablishment.