In fish farmings, diseases can be reduced by using immunostimulants. The aim of this study was to evaluate the immunostimulant potential of Mentha piperita in tambaqui fed with 0, 0.5, 1.0 and 1.5% of oil per kg of commercial fish feed. The fish were inoculated with Aeromonas hydrophila to challenge them. Hematological and biochemical parameters were determined after 30 days of feeding and seven days after the challenge. There was no mortality and M. piperita oil did not influence fish production parameters. However, blood hemoglobin concentration (Hb) increased in the fish fed with 0.5 and 1.5% of oil per kg of diet; albumin increased in those fed with 1.0%; cholesterol increased in all groups with oil; and triglycerides increased in those fed with 0.5%. After the bacterial challenge, the fish showed decreases in Hb when fed with diet enriched with 1.5% oil per kg of diet, in mean corpuscular volume with 1.0% and in mean corpuscular hemoglobin concentration with 0 and 1.5%. Protein levels increased in groups with 0 and 1.5% of oil and albumin when fed with 0 and 1.0%; cholesterol levels increased in the control group; and high levels of triglycerides were observed in the groups with 0, 0.5 and 1.5%. Thus, M. piperita essential oil promoted hematological alterations in tambaqui and can be recommended in diets containing up to 1.0% per kg, because of the minimal physiological modifications caused. However, additional studies are necessary to obtain more information regarding to the physiological effects of this immunostimulant. KEYWORDS: Immune system; natural product; bacterial challenge; biochemistry.Respostas hematológicas de tambaqui Colossoma macropomum (Serrassalmidae) alimentado com dietas suplementadas com óleo essencial de Mentha piperita (Lamiaceae) e desafiados com Aeromonas hydrophila RESUMO Em pisciculturas, doenças podem ser minimizadas com o uso de imunoestimulantes. O objetivo deste estudo foi avaliar o potencial imunoestimulante do óleo essencial de Mentha piperita na dieta de tambaqui com dietas contendo 0; 0,5; 1,0; 1,5% de inclusão do óleo por kg de ração comercial para peixes. Os tambaquis foram desafiados com a bactéria Aeromonas hydrophila. Hematologia e bioquímica dos tambaquis foram determinados após 30 dias de alimentação e sete dias do desafio. Não houve mortalidade dos peixes durante o experimento, sendo que o óleo não influenciou os parâmetros produtivos dos peixes. Entretanto, a concentração de hemoglobina (Hb) aumentou em peixes alimentados com 0,5 e 1,5% de óleo por kg de dieta; a albumina aumentou em 1,0%; o colesterol aumentou em todos os grupos com óleo; e triglicérides em 0,5% por kg de dieta. Após desafio bacteriano ocorreram diminuições da Hb nos peixes alimentados com 1,5% de óleo; do volume corpuscular médio com 1,0%; e da concentração de hemoglobina corpuscular média com 0 e 1,5%. Níveis aumentados de proteína nos grupos 0 e 1,5%; da albumina em 0 e 1,0%; do colesterol no controle; e dos triglicérides em 0, 0,5 e 1,5% de óleo na dieta. Assim o óleo essencial de M. ...

Immunostimulants in farmed fish diets has been considered an effective approach to health management. This study aimed to assess antioxidant effects and resistance against pathogens of Colossoma macropomum (tambaqui) fed essential oil (EO) of M. piperita at 0%, 0.5%, 1.0% and 1.5% kg −1 commercial feed during 30 days. Tambaqui were challenged with Aeromonas hydrophila and did not present clinical signs of alterations. Higher hepatic catalase activity was observed in fish fed 1.0% of M. piperita EO, compared with 1.5%. Renal superoxide dismutase and glutathione peroxidase decreased in the fish fed M. piperita EO. Hepatic and renal lipid hydroperoxide increased among fish fed diets with 1.0 and 1.5% of EO. Tambaqui fed 1.0% of M. piperita EO showed respiratory activity increase, compared with 0.5%. Monocytes and PAS-GL were abundant in fish fed higher EO concentrations. Reduction in monogenoideans abundance was observed in fish fed 0.5 and 1.0% of EO. Although anti-helminth effects were observed, M. piperita EO in tambaqui diet did not promote leukocytes and lysozyme activity increases at the concentrations assessed. It can be suggested that other concentrations should be tested in future studies, as the combined use with other products, such as immunostimulants and probiotics.