Anestesia e transporte de Colossoma macropomum com os óleos essenciais de Aloysia triphylla, Lippia sidoides e Mentha piperita

Abstract

Tambaqui (Colossoma macropomum) is the most produced native species in Brazil. However, due to the great demand, the increase in stocking densities in breeding environments, in addition to the innumerable management practices that have been carried out inappropriately, have caused deleterious effects for the breeding stock. In order to minimize these effects, numerous commercial products have been used in aquaculture to reduce the effects of stress. In the last decade, many studies have described the need to evaluate alternative products from plant species, which have anesthetic properties, especially those aimed at reducing the stress associated with fish transport. Thus, the objective of the work was, in a first step, to carry out a literature review in order to describe the anesthetic and stress-reducing potential of essential oils in native fish, with special emphasis on C. macropomum. Following, from experimental designs implanted in Embrapa Amazônia Ocidental experimental field, essential oils from three vegetable sources - Aloysia triphylla (EOAT), Lippia sidoides (EOLS) and Mentha piperita (EOMP) - were evaluated in order to determine the time and concentrations necessary for anesthetic induction and recovery in tambaqui and the evaluation of morphophysiological responses to stress due to transport under the influence of essential oils. To achieve these goals, the plants were grown in the medicinal plant sector of Embrapa Amazônia Ocidental, with essential oils extracted and chemically characterized by mass spectrophotometry and gas chromatography. The fish - juveniles of C. macropomum - were purchased at a commercial fish farming station in the municipality of Rio Preto da Eva - AM and transported to the Embrapa experimental field in Manaus, where they passed through the breeding phase until they reached the desired size for the fish experiments. In the first test, to determine the time and the necessary concentration of essential oils for anesthetic induction and recovery, the fish were individually exposed to different concentrations of essential oils (EOAT: 5, 10, 20, 40, 60, 80 and 150 mg L-1; EOLS: 2, 5, 10, 20, 30, 40 and 50 mg L-1; EOMP: 5, 10, 20, 40, 60, 70 and 90 mg L-1), in a period between four minutes at six hours of exposure. The three essential oils showed anesthetic properties. The concentration intervals at which the fish reached all stages of anesthesia were (1, 2, 3a, 3b, 4) were between 40 to 150 mg L-1 for EOAT, 20 to 50 mg L-1 for EOLS and 40 to 90 mg L-1 for EOMP. The exposure of C. macropomum to anesthetic concentrations of oils was not associated with an increase in the occurrence of irreversible damage to the gill lamellae. In the second trial, the essential oils of L. sidoides and M. piperita were evaluated as stress reducers in the transport of C. macropomum. The fish (127.55 ± 22.41 g) were transported for four hours in plastic bags, comprising the following treatments: a) non-stressed control (NS - not subjected to transport), b) stressed control (S - subjected to transport), c) EOLS 10 mg L-1, d) EOLS 20 mg L-1, e) EOMP 20 mg L-1 and f) EOMP 40 mg L-1, with three repetitions. After transport, water quality, hormonal, biochemical and enzymatic parameters were analyzed. C. macropomum transported with EOLS 20 mg L-1 showed a significant reduction in cortisol levels when compared to fish transported without essential oil. The glycolytic pathway was especially stimulated in fish transported with EOMP 20 mg L-1, since the values of glycolytic enzymes hexokinase (HK), pyruvate kinase (PK) and lactate dehydrogenase (LDH) were elevated in muscle tissue. The essential oils did not affect the activity of acetylcholinesterase (AChE) in the brain of C. macropomum, and after transport, fish from all treatments showed a significant reduction (28.2%) in muscle AChE. The EOLS 20 mg L-1 and EOMP 20 mg L-1 concentrations increased the levels of the glutathione S-transferase (GST) enzyme in the brain. It is concluded that essential oils in the concentrations evaluated tend to improve water quality during transport, minimize physiological stress, help maintain energy demand through the glycogen pathway and, in addition, do not demonstrate neurotoxic effects, recommended to concentration of 20 mg L-1 EOLS for use in the transport of C. macropomum. Given the results presented, the perspectives open up for the evaluation of compounds isolated from essential oils, as well as nanomolecules in order to increase the effectiveness of essential oils and enhance their biological activities, such as anesthetic and stress-reducing activities. With the provision of this information, it is intended to contribute to the development of the productive sector, leading to greater biosecurity and biosafety in the aquaculture segment.