Parasites in Leporinus macrocephalus (Anostomidae) of four fish farms from the western Amazon (Brazil).

This study evaluated the presence of metazoan parasites in Leporinus macrocephalus from four fi sh farms from the western Amazon (Brazil). In 160 fish examined, prevalence was 61.9%, and parasites found were: Urocleidoides paradoxus, Urocleidoides eremitus, Tereancistrum parvus, Jainus leporini, Procamallanus (Spirocamallanus) inopinatus, Rhabdochona (Rhabdochona) acuminata, Dolops discoidalis and Ergasilus sp., but U. paradoxus was the dominant parasite. Jainus leporini and Ergasilus sp. occurred only in L. macrocephalus from one fi sh farm, while U. paradoxus, U. eremitus and T. parvus were found in fi sh from three fi sh farms. Dolops discoidalis, P. (S.) inopinatus and R. (R.) acuminata occurred only in L. macrocephalus from two fi sh farms. Higher infection levels were caused by U. paradoxus, U. eremitus and P. (S.) inopinatus, which had an aggregated dispersion. There was positive correlation between abundance of parasites and the length of hosts. No difference in the condition factor of parasitized and non-parasitized fi sh were found. Such differences between fish farms were attributed to differences in management and quality of cultivation environments, and data indicate the need to adopt prophylactic measures in the fish farms to prevent diseases in the future. This was the fi rst report of D. discoidalis and Ergasilus sp. for L. macrocephalus.The in vitro efficacy of the essential oil of Piper callosum, Piper hispidum and Piper marginatum against monogeneans and the tolerance of Colossoma macropomum to these oils was assessed. Concentrations of these essential oils were tested, and two control groups were used: one with water from the cultivation tank only and the other with water from the cultivation tank + 70% alcohol, the solvent for these essential oils. For all the concentrations of P. callosum, 100% efficacy against Anacanthorus spathulatus, Notozothecium janauachensis, Mymarothecium boegeri and Linguadactyloides brinkmanni occurred after 5 min of exposure. At concentrations of 600 and 800 mg/L of P. hispidum, 100% in vitro efficacy occurred after 20 min of exposure. At concentrations of 200, 300 and 400 mg/L of P. marginatum, 100% efficacy occurred after 1 h of exposure. In the control groups using water from the tank + alcohol, the total immobilization of the monogeneans varied, while in the control groups with water from the cultivation tank, the total immobilization of monogeneans only occurred after 9 h of exposure. Little structural damage to the tegument of the parasites exposed to P. callosum, P. hispidum and P. marginatum was observed on scanning electron microscopy. The tolerance of C. macropomum for P. callosum, P. hispidum and P. marginatum was assessed and discussed. The results suggest that the essential oils of P. callosum, P. hispidum and P. marginatum possess high in vitro efficacy against monogeneans of C. macropomum and thus require testing in therapeutant baths for use in aquaculture.