Levamisole promotes an adjuvant effect on the immunity of pacu (Piaractus mesopotamicus) when immunized with Aeromonas hydrophila, even when provided in the diet

AbstractDietary immunomodulators can help to defend against disease, but their dosage and time of administration are not always clear in aquaculture. In this study, we analyzed the amount of dietary levamisole required to induce an adjuvant effect. Because immunostimulants and immunization can improve the fish immune system, this study evaluated the effects of dietary levamisole administration (at 0, 125, 250 and 500mg/kg diet) and immunization with A. hydrophila (1×109 CFU) on the acquired and innate immune systems of pacu (mean initial weight 176.03±15.73g). The results showed that levamisole can act as an adjuvant for vaccination, even when administered through the diet. Immunization and levamisole administration increased the antibody titer, serum bactericidal activity, and hematocrit as well as the numbers of red blood cells, leukocytes and thrombocytes in pacu (P<0.05). However, the lysozyme activity; leukocyte respiratory activity; total protein, albumin, and globulin levels; A:G index; corpuscular hemoglobin volume; and other white blood cells showed no differences when compared with the control fish. As the immunostimulant improved, certain parameters of the acquired and innate immune systems of pacu increased, and the administration of levamisole in the diet (125 or 250mg/kg) for seven days may be used to promote adjuvant effects during immunization with A. hydrophila and thus constitutes a feed protocol strategy to be used prior to immunization

Serum bactericidal activity as indicator of innate immunity in pacu Piaractus mesopotamicus (Holmberg, 1887)

The immune system of teleost fish has mechanisms responsible for the defense against bacteria through protective proteins in several tissues. The protein action can be evaluated by serum bactericidal activity and this is an important tool to analyze the immune system. Pacu, Piaractus mesopotamicus, is one of the most important fish in national aquaculture. However there is a lack of studies on its immune responses. In order to standardize and assess the accuracy of the serum bactericidal activity assay, fish were briefly challenged with Aeromonas hydrophila and sampled one week after the challenge. The bacterial infection increased the concentration of protective proteins, resulting in a decrease of colony-forming unit values expressed as well as an enhanced serum bactericidal activity. The protocol showed a reliable assay, appropriate to determine the serum bactericidal activity of pacu in the present experimental conditions.O sistema imune de peixes teleósteos tem mecanismos responsáveis pela defesa contra bactérias e atua através de proteínas presentes em diversos tecidos. A ação destas proteínas pode ser avaliada pela atividade bactericida do soro, sendo esta uma importante ferramenta para analisar o sistema imune. O pacu, Piaractus mesopotamicus, é um peixe nativo muito importante para aquicultura nacional, entretanto há pouco conhecimento sobre o funcionamento de seu sistema imune. Assim foi realizado experimento para padronizar e avaliar a eficiência do ensaio de atividade bactericida. Resumidamente, peixes foram desafiados por Aeromonas hydrophila e amostradas uma semana após o desafio. A infecção bacteriana promoveu um aumento na concentração de proteínas protetoras, resultando em diminuição dos valores de unidades formadoras de colônias ou expressos também como aumento da atividade bactericida do soro. O protocolo se mostrou confiável, sendo apropriado para determinar a atividade bactericida do soro de pacu nas condições experimentais.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES