Parasitology of juvenile mullet (Mugil liza) and effect of formaldehyde on parasites and host

Abstract: Few studies have been performed with parasites of marine and estuarine fish in southern Brazil. In the present study, unpublished results show the ways of parasitism of juvenile mullet by parasites. The toxicity of formaldehyde and the effectiveness of this chemotherapy in controlling parasites in reared juvenile mullet Mugil liza were also studied. Juvenile mullets (1±0.26g; 4.1±0.4cm) were exposed to different concentrations of 37% formaldehyde: control group and five formaldehyde concentrations which were tested: T1 (13.5), T2 (21.6), T3 (40.5), T4 (81) and T5 (135) mg L−1 with 8 fish per repetition in triplicate. To verify the drug effectiveness in parasitic control, juvenile mullets were exposed to 1h prophylactic bath of 37% formaldehyde with a control group and five formaldehyde concentrations: T1 (67.5), T2 (135), T3 (270), T4 (405) and T5 (540) mg L−1, 8 fish per repetition in triplicate. Ligophorus cf. uruguayensis (Monogenoidea: Ancyrocephalidae) and Solostamenides cf. platyorchis (Monogenoidea: Microcotylidae) were identified in the gills. Digenea and Nematoda were observed in the intestines. This is the first occurrence of S. cf. platyorchis in Brazil. During the toxicity test, the LC50-96h was estimated at 20.77mgL−1 of formaldehyde. During the 1h formaldehyde prophylactic bath, all parasites were eliminated in formaldehyde concentrations between 135 and 540mgL−1. High survival rate was observed in all treatments. Values of prevalence and intensity of infestation observed in this study showed the potential damage caused by Monogenoidea to mullet. Formaldehyde baths with 135mgL−1 are recommended to control Monogenoidea in mullet and the safe limits for formaldehyde use were presented. Besides, the endoparasites were tolerant to formaldehyde exposure. [Copyright &y& Elsevier]