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This study evaluated the effect of short‐term baths with the essential oils (EOs) of Lippia sidoides, Ocimum gratissimum and Zingiber officinale on the survival, haematological, biochemical and histopathological parameters of native fish tambaqui (Colossoma macropomum), challenged with Aeromonas hydrophila. After challenge, the fish infected with A. hydrophila received therapeutic baths of 60 min, for five consecutive days. Treatments were as follows: challenged and not treated; challenged and treated with 10 mg L−1 of gentamicin; challenged and treated with EO of L. sidoides (2.5 and 5.0 mg L−1); challenged and treated with EO of O. gratissimum (5.0 and 10.0 mg L−1); challenged and treated with Z. officinale EO (5.0 and 10.0 mg L−1). The highest survival rates were 89.5% (fish treated with 5.0 mg L−1 of O. gratissimum EO) and 75.0% (fish treated with 5.0 mg L−1 of L. sidoides EO). Reductions in the haematocrit percentage, haemoglobin and erythrocyte number were observed in fish treated with L. sidoides and Z. officinale EOs compared with control fish. Mild to moderate damage to the liver tissue of fish after challenge and EO treatments were observed. It is suggested that baths containing O. gratissimum and L. sidoides EOs consist in a viable treatment to increase survival rates of C. macropomum infected with A. hydrophila. [ABSTRACT FROM AUTHOR]

Neoechinorhynchus buttnerae is the only acanthocephalan species that has been detected infecting tambaqui (Colossoma macropomum) in northern Brazil. This helminth greatly affects nutrient uptake in fish and leads to cachexia and economic losses of up to 100% in tambaqui production. This study investigated the efficacy, in vitro and in vivo, of a food additive (Acantex) to control N. buttnerae in tambaqui, as well as its effects on fish blood parameters and possible effect on monogeneans. For the in vitro assay, the parasites were exposed to nine concentrations (1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 mg/kg) of Acantex and one control (without the product). For the in vivo assay, 120 naturally infected tambaqui were distributed into twelve tanks (10 fish per tank) and were divided into four treatments, in triplicate. Fish were fed with commercial feed containing 0.0, 3.0, 4.0 and 5.0 mg/kg of Acantex, for 25 days. Acantex at 3.0 mg/kg showed 100% efficacy against N. buttnerae in in vitro testing, after exposure for 2 hr. In vivo efficacy was 13.46% at 3.0 mg/kg against the endoparasite N. buttnerae and caused a mortality rate of 19%–37% of monogeneans. Blood and biochemical parameters suggested that fish were malnourished due to attached intestinal parasites and the resulting competition for nutrient uptake. Acantex did not show adequate efficacy in treating acanthocephalosis under the conditions of this study; therefore, more efficient forms of Acantex administration in the diet of tambaqui are warranted to eliminate acanthocephalans. [ABSTRACT FROM AUTHOR]

Phytotherapy can replace antibiotic administration as an alternative to control Aeromonas hydrophila, one of the main bacteria involved in the aetiology of farmed fish diseases. Given that plants of the Lippia spp. genus show biological potential for antimicrobial activity, this study evaluated the chemical composition of essential oils extracted from Lippia alba, Lippia origanoides and Lippia sidoides and their activity against A. hydrophila. The oils were obtained by steam distillation in a Clevenger-type apparatus and their composition determined by gas chromatography and mass spectrometry (CG/MS). Antibacterial activity was assessed by calculating the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using broth microdilution method. The main compounds identified were geranial (25.4%) and neral (16.6%) in L. alba oil, carvacrol (40.4%) and p-cymene (11.4%) in L. origanoides oil and thymol (76.6%) and ortho-cymene (6.3%) in L. sidoides oil. The three Lippia species showed bacteriostatic and bactericidal action against A. hydrophila, with MICs and MBCs ranging from 1250 to 5000 μg mL−1. Of the species tested, the best performance was obtained with essential oil of L. sidoides. [ABSTRACT FROM AUTHOR]