Atividade antiparasitária dos óleos essenciais de Aloysia triphylla, Lippia gracilis e Piper aduncum no controle de Piscinoodinium pillulare em Colossoma macropomum

Abstract

Piscinoodinium pillulare is an ectoparasite recognized worldwide by large-scale outbreaks in fish farms, and registered in tambaqui, Colossoma macropomum, the most produced native fish species in Brazil. The search for natural products as an alternative to synthetic ones for the treatment of fish diseases has grown in recent years, due to their biodegradable properties and less possibility of causing parasite resistance. Given this scenario, the aim of this study was to evaluate the antiparasitic activity of essential oils (EOs) from Aloysia triphylla, Lippia gracilis and Piper aduncum for the control of P. pillulare in juvenile tambaqui. Firstly, the acute toxicity of the three EOs was evaluated in a completely randomized design (DIC), with six treatments: the control and five concentrations of EOs (A. triphylla 60, 80, 100, 120 and 140 mg L-1, L. gracilis 35, 40, 45, 50 and 55 mg L-1 and P. aduncum 42.5, 45, 47.5, 50 and 52.5 mg L-1), with three replicates and a 4hour exposure. This procedure aimed to define safe concentrations for application in therapeutic baths, which were also based on literature data, followed by pilot tests. The results showed that the mortality and severity of damage to the tambaqui gills were proportional to the increase in the concentrations of the EOs, with the mean lethal concentration (LC50-4 h) estimated at 109.57 mg L-1 for A. triphylla, at 41.63 mg L-1 for L. gracilis and at 48.17 mg L-1 for P. aduncum. Grade II and grade III histopathologi-cal damage were of low frequency, and the latter, which includes severe and irreversible al-terations, was recorded only in the highest concentrations of P. aduncum EO (47.5, 50.0 and 52.5 mg L-1). Therefore, EO concentrations below the LC50-4 h can be used for short expo-sure periods. This protocol was adopted in the second phase of this study in order to deter-mine the effectiveness of the three EOs in the treatment of P. pillulare in tambaqui after ap-plication of three therapeutic baths of 15 minutes. For this, a DIC with seven treatments and three replications was used: control, EOs of A. triphylla (40 and 50 mg L-1), L. gracilis (20 and 30 mg L-1) and P. aduncum (10 and 20 mg L-1). After treatments with essential oils, P. pillulare was quantified in a sedgewick rafter câmara using three aliquots of each sample to determine the parasitic indices of prevalence, mean abundance and mean intensity, as well as the antiparasitic efficacy. To assess the physiological state of fish, analyzes of hematocrit, erythrocyte counting, hemoglobin, glucose, total proteins, and the activity of the enzymes aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase were deter-mined. The effectiveness of EOs in controlling P. pillulare ranged from 63.8 to 83.8%. There was no significant difference between treatments for hematological and biochemical parame-ters, but the infestation by P. pillulare promoted a reduction in hematocrit and hemoglobin, in addition to an increase in plasma glucose and total proteins. For enzymatic parameters, there was a reduction in alanine aminotransferase, but there was no impairment of liver func-tion in tambaqui. Therefore, the EOs of A. triphylla, L. gracilis and P. aduncum are good therapeutic alternatives to mitigate the negative impacts caused by the infestation of P. pillu-lare in the tambaqui rearing.