Óleos essenciais de Myrcia sylvatica (G. Mey.) DC. e Curcuma longa L. como anestésicos para peixes: efeitos sobre as respostas fisiológicas

Abstract

The use of anesthetic substances is necessary to reduce stress and provide fish welfare during aquaculture practices. The aim of this study was to investigate the use of Myrcia sylvativa (EOMS) and Curcuma longa (EOCL) essential oils (EOs) as anesthetics in different fish species and the possible effects on the physiological responses of these organisms. Firstly, efficacy of EOMS and EOCL as anesthetics for Colossoma macropomum (tambaqui) was determined, and the effects of anesthesia and sedation with these EOs were evaluated. Fish were divided into 8 groups and exposed to anesthetics (200 μL/L EOMS and 500 μL/L EOCL) and sedatives (10 μL/L EOMS and 40 μL/L EOCL) concentrations for 5 min and 6 h, respectively; or, simulation of anesthesia and sedation (control and ethanol groups, times of 5 min and 6 h, without use of anesthetics). After exposure, plasma and tissues were collected to evaluate the primary (cortisol) and secondary (biochemical indexes, hepatic metabolism, oxidative biomarkers) indicators of stress (article1). In a second step, biochemical and oxidative effects were investigated in plasma and tissues of Brycon amazonicus (matrinxã) exposed to rapid anesthesia (5 min) or prolonged sedation (360 min, simulating transport) with EOMS (200 μL/L and 10 μL/L , respectively) and EOCL (500 μL/L and 40 μL/L, respectively) (article 2). Finally, effects of the initial manipulation and addition of EOMS in transport on the activation of stress pathways in Rhamdia quelen (jundiá) were investigated. The fish were captured, transferred to 100 L tanks (density 100 g/L) and sampled after 24 h (pre-transport group). The remaining fish were placed in plastic bags containing 5 L of water (density 150 g/L) with different concentrations of EOMS (0, 25 or 35 μL/L, diluted in 315 μL/L ethanol) and transported for 6 h. Stress and metabolism indicators, as well as mRNA expression of different hormones were evaluated. Previously, cDNAs encoding corticotropin releasing hormone (CRH) and two subunits of proopiomelanocortin (POMCa and POMCb) were cloned from the brain and pituitary of jundiá, respectively (manuscript). The two EOs were effective as anesthetic for C. macropomum at concentrations of 100, 200 and 300 μL/L of EOMS and 200, 300 and 500 μL/L of EOCL. Anesthesia and sedation with EOs reduced lipid peroxidation (LPO) levels, and increased the activity of antioxidant enzymes (superoxide dismutase-SOD, catalase-CAT, glutathione peroxidase-GPx, glutathione reductase-GR and glutathione-S-transferase-GST), the content of non-protein thiols and the total antioxidant capacity in tissues of tambaqui, relative to control group (article 1). In turn, transport simulation (without EOs) increased LPO levels in the gills and kidney of matrinxã; this parameter was reduced in the brain, gills, liver and kidneys of fish sedated and anesthetized with EOs. Anesthesia with EOs increased SOD and GST activity in the brain, and CAT in the liver and gills. Prolonged sedation with EOs increased SOD, GPx and GR activity in the brain, CAT in the liver, GPx and GR in the gills, and SOD in the kidney. The content of non-protein thiols and the total antioxidant capacity of tissues increased after anesthesia and sedation with EOs (article 2). Cortisol levels and CRH expression increased after 24 h of capture and handling of jundiá, while glucose levels increased after transport. The addition of EOMS during transport reduced cortisol and lactate levels in relation to control. Expression of CRH, POMCb, prolactin and somatolactin mRNAs was lower after transport with EOMS than control, suggesting the involvement of these hormones in the activation of stress pathways caused by pre and post-transport events (manuscript). Thus, the use of EOMS and EOCL as sedatives and anesthetics in aquaculture practices is suggested to improve survival and animal welfare, respecting recommended concentrations, for stress reduction and antioxidant protection of tissues.