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Several routine aquaculture practices, such as densification, handling and transport, are considered potential stressors and can cause physiological alterations that compromise the animals' welfare and survival. Studies of plant‐based anaesthetic products have become a trend worldwide, mainly due to their potential uses and the variety of species that can provide suitable substances. In Brazil, the use of essential oils (EO) in fish farming for use in sedation and anaesthesia has already been explored. However, despite the excellent biological activity of the EO, as a result of their main compounds or due to the synergy between the active compounds, it is also necessary to investigate the adverse effects that they can cause and accordingly establish the appropriate dosage for their use. Sedative and anaesthetic properties of the EOs of at least 30 plant species have been described for native fish species reared in Brazil such as Colossoma macropomum, Rhamdia quelen, Brycon amazonicus, Lophiosilurus alexandri, Piaractus mesopotamicus, P. mesopotamicus × C. macropomum, Pseudoplatystoma reticulatum and Serrasalmus rhombeus. However, the mechanisms of action of the EOs need to be elucidated, as well as the undesirable side effects they may cause in fish. This review presents information on the use of EOs as anaesthetics and sedatives in native fish species farmed in Brazil, with emphasis on C. macropomum and, as a future perspective, the application of new technologies is emphasized to potentialize the biological activities of EOs, thus contributing with environment‐friendly natural alternatives for the promotion of sustainable aquaculture. [ABSTRACT FROM AUTHOR]

The objective of this study is to identify the economic–financial viability, attractiveness potential, and investment risks of tambaqui farming in the state of Amazonas, Brazil. Tambaqui is the main native fish in Brazilian aquaculture. A survey was conducted for 240 fish farms, and analyzed through Monte Carlo simulations. It was found that fluctuation in feed (US$0.49 ± 0.09 kg−1) and fish prices (US$1.77 ± 0.48 kg−1) exerts a great influence on the profitability of the projects. In general, the results indicate that it is difficult to make the farms profitable. The use of modern technologies, such as aerators, and monosex populations on fish farms may be some alternatives to overcome this situation and improve the productivity of the sector, consequently promoting its sustainability. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the anesthetic potential of the essential oils of Aloysia triphylla (EOAT), Lippia sidoides (EOLS) and Mentha piperita (EOMP) in relation to juvenile tambaqui (Colossoma macropomum), based the swimming behavior of these fish and possible histopathological damage to the gills. To induce anesthesia, juvenile tambaqui (130.55 ± 22.4 g; 16.8 ± 0.95 cm) were individually exposed to different concentrations of the 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), for exposure periods of between four minutes and six hours. The three essential oils evaluated presented anesthetic properties. The concentration intervals over which the fish reached all the stages of anesthesia (1, 2, 3a, 3b and 4) were between 40 and 150 mg L−1 for EOAT; 20 and 50 mg L−1 for EOLS; and 40 and 90 mg L−1 for EOMP. The times taken to reach the anesthesia stages were inversely proportional to the increases in the concentration of the essential oils. The histopathological damage to the gills of the tambaqui that resulted from using essential oil concentrations that were defined as anesthetic (150 mg L−1 EOAT, 30 mg L−1 EOLS and 90 mg L−1 EOMP) were also evaluated. The main damage recorded was hypertrophy and hyperplasia of the lamellar epithelium, lamellar fusion and proliferation of chloride cells. According to the histopathological alteration index (HAI), there were no irreversible damage (such as fibrosis and necrosis) to the gills of the tambaqui. However, while EOLS and EOMP caused mild damages in the gills, the EOAT generated more severe damages. Overall, for the tambaqui, the essential oils of A. triphylla, L. sidoides and M. piperita are efficient anesthetic in the doses of 150, 30 and 90 mg L−1, respectively. • This study reports the sedative and anesthetic effects of Aloysia triphylla , Lippia sidoides and Mentha piperita essential oils on Colossoma macropomum. • The essential oil of L. sidoides (30 mg L-1) induced faster anesthesia and recovery in C. macropomum. • Essential oils of A. triphylla , L. sidoides and M. piperita caused no irreversible damage to the gills of C. macropomum. [ABSTRACT FROM AUTHOR]