Ação do óleo essencial de Hyptis mutabilis em Rhamdia quelen parasitados com Ichthyophthirius multifiliis e seus efeitos em peixes sadios

Abstract

The aim of this study was to evaluate the activity of leaves essential oil (EO) of Hyptis mutabilis, as well as its major constituent (-)-globulol against the fish parasite Ichthyophthirius multifiliis (Ich) and their effects on hematological, biochemical and immunological parameters in silver catfish (Rhamdia quelen). In the first experiment lasting four days, naturally infected fish were treated with EO (0, 10 and 20 mg.L-1 and 199.26 μL.L- 1 ethanol) by means of different exposure methods (a single application at the beginning of the experiment, twice with a 48 h interval, and 1 h daily baths). Fish mortality and the number of parasites (trophonts per fish) were assessed after 48 and 96 h. The 1 h daily baths provided the best survival when compared to a single application and two applications with a 48 h interval, and this methodology was set for the second experiment, in which infected animals were exposed to (-)-globulol at 2.5 and 5 mg.L-1. The most effective concentrations in the experiments 1 and 2 were chosen for experiment 3, in which healthy animals were subjected to 1 h daily baths with EO (20 mg.L-1) or (-)-globulol (2.5 mg.L-1). Four days later, the animals had hematological, biochemical, and immunological parameters assessed. After exposure of healthy animals to EO, significant increase was detected in hematocrit (28.42 %), erythrocytes (2.11 106 μL-1) and leukocytes (48.82 103 μl-1), while the total count of thrombocytes (20.50 103 μL-1) decreased in comparison to previous studies with Rhamdia quelen. However exposure to (-)-globulol increased only the leukocyte number (70.87 103 μl- 1) related to the default values already reported to this species. Total cholesterol showed elevated levels (226.66 mg dL-1) in fish exposed to EO, while the group treated with (-)- globulol presented higher LDL (244.66 mg dL-1) and lower HDL (87.66 mg dL-1) values than the control and ethanol groups. EO and (-)-globulol increased survival of fish infected with ich and altered some hematological and biochemical parameters, such as such as albumin, total cholesterol, HDL, LDL, hematocrit, erythrocytes, leucocytes, thrombocytes and MCV. No significant differences were detected in nonspecific immune assay between the treated groups and control, indicating that the EO and (-)-globulol did not increase innate immunity of fish.