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The objective of this work was to evaluate peppermint (Mentha piperita) essential oil toxicity to and potential as an anesthetic for juvenile silver catfish (Rhamdia quelen). To determine the lethal concentration at 4 hours (LC50-4h), 210 fish (3.08±0.8 g and 7.59±0.67 cm) were exposed to 0, 20, 50, 80, 110, and 140 mg L-1 essential oil. To evaluate the anesthetic potential, nine fish were individually exposed to each oil concentration (50, 80, 110, and 140 mg L-1) used. Water quality parameters were controlled. The mortality rate and the severity and extent of the gill injuries of silver catfish juveniles at 4 hours of exposure increased with increasing peppermint essential oil concentrations, with LC50-4h estimated to be 75.06 mg L-1. The main gill injuries were: congestion of the venous sinus of the primary lamella and at the base of the secondary lamella; interlamellar hyperplasia with fusion of lamellae; epithelial detachment; dilation of the venous sinus; edema adjacent to the lamella; and aneurysm. However, this oil is an effective anesthetic for silver catfish juveniles at the concentration of 80 mg L-1, with a short time of anesthesia (<4 min) and recovery (<10 min), with no mortality.

Aim Aquaculture plays an important role in the world and in Brazil. Artificial construction of water bodies, such as ponds and reservoirs, has allowed for fish culture in cages in those environments, generating conflicts over the use of these public waters. The producers are seeking to increase production, and the ecosystem is susceptible to the impacts caused by production activity. The aim of this review was to identify questions about these conflicts (productivity × environment) and to indicate possible solutions to the main problems related to fish farming in reservoirs. Methods A bibliographical survey was carried out on the main aspects of cage fish farming in Brazilian reservoirs. Studies from 1977 to 2018 (scientific journals, books, and thesis) were revised using seven databases, the CAPES periodicals portal and Google Scholar websites. The main keywords used were “aquaculture”, “reservoir”, “cage”, “eutrophication”, “carrying capacity”, “impacts”, “oligotrophic”, “escapes”, “hybrids”, and “pollution”. Results We accessed approximately 330 and cited 151 documents. Conclusions The negative aspects associated with cage fish farming, as escapes of cultivated fish, and the possible solutions of this and others negative impacts were addressed, identifying mechanisms for reducing conflicts between environmental impacts and aquaculture production. Potential solutions include the use of native fish species or sterile species, implementation of monitoring systems of the surrounding area, adoption of measures to reduce the accidental escape of fish, use of multitrophic culture systems, use of highly digestible diets with appropriate food management, and use of computer programs that incorporate current and historical environmental data to calculate carrying capacity and choose the most appropriate location for production.

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