Antiparasitic efficiency and toxicity of levamisole in juveniles of Mugil liza Valenciennes, 1836 submitted to therapeutic baths
Author: Jacqueline Cristina de Oliveira Xavier (Currículo Lattes)
Supervisor: Dr Joaber Pereira Junior
Co-supervisor: Dr Rogério Tubina Vianna
Mullets (Mugil spp.) Are one of the main groups of marine fish with breeding potential for aquaculture in Brazil. The high densities to which the fish are subjected under confinement conditions increase the chances of parasites occurring, which can cause damage to fish farms and/or cause zoonoses transmitted by the fish. In Brazil, studies related to the efficacy of antiparasitic drugs for fish and their side effects are scarce, and therefore studies are needed to assess the efficiency and impacts of these drugs before they can be used on a large scale in commercial fish farms.The objective of this work was to evaluate acute toxicity and antiparasitic efficiency on branchial ectoparasites of different concentrations of levamisole in 24-hour therapeutic baths in juveniles of Mugil liza. For the development of this study, mullets with an average length of 2.9 cm were used, collected in the nature in a stream that flows into Praia do Cassino (31º 11 '55 ”S; 52º 11' 14” O), transported to the laboratory and acclimated in 80 liter plastic boxes with constant aeration. To determine the toxicity level of levamisole and the concentrations used in the antiparasitic efficiency experiment, an LC50-24h test was performed. The treatments were carried out in triplicate conducted in a completely randomized design.To calculate the LC50, the software “Trimmed Spearman Karber Method” was used, which determined that the LC50-24h of levamisole for juveniles of the mullet M. liza was 61.63 mg/L. The parasitological indices (Prevalence, Intensity of Infestation and Average Abundance) of mullets in the wild were determined through a parasitological examination previously performed on a sample containing 30 fish. Through parasitological analyzes it was concluded that, in juveniles of M. liza on the coast of Rio Grande do Sul, Ligophorus cf. uruguayense, Solostamenides sp. and Girodactilus sp. in the gills of juveniles of M. liza, which function as an infestation site. Based on the results of the LC50-24h test of levamisole in M. liza, 3 concentrations were chosen (0; 7.5; 15 and 22,5 mg/L) that would guarantee that the fish survival was greater than 50% in each treatment. All treatments were performed with three replications. Under the conditions in which the experiment was carried out, it was possible to conclude that 15 mg/L levamisole is indicated in the control of Gyrodactylus sp. for juveniles of M. liza. For the control of Solostamenides sp. it was not possible to evaluate the effectiveness of levamisole due to the null prevalence found in the control group for this parasite. Considering the low efficiency of the concentrations tested in the 24-hour prophylactic baths in the control of L. uruguayense, the use of this method in this exposure time is not recommended in the treatment against this Monogenoidea.