Trichlorfon is effective against Dawestrema cycloancistrium and does not alter the physiological parameters of arapaima (Arapaima gigas): A large Neotropical fish from the Amazon.

Abstract

This study investigated the in vitro and in vivo efficacy of trichlorfon against Dawestremacycloancistrium, as well as its physiological effects on arapaima. Naturally parasitized arapaima gill arches were exposed in vitro to 100, 250, 500 and 750mg/L of trichlorfon and a control group (only distilled water), in triplicate. Parasites were monitored, and mortality was used to determine the median effective concentration (EC50 ). The 750mg/L concentration demonstrated 100% in vitro efficacy against D.cycloancistrium after 60min, while the intermediate (500mg/L) and the lowest (100 and 250mg/L) tested concentrations were completely efficient after 90 and 130min, respectively. The EC50-1h of trichlorfon for D.cycloancistrium was determined at 171.73mg/L. Parasitized arapaima juveniles were exposed to a control group and 150mg/L of trichlorfon in triplicate. Fish were exposed to two therapeutic baths for 60min with 24-h intervals between treatments. Therapeutic baths with 150mg/L of trichlorfon were 92.99% effective against D.cycloancistrium and did not bring about haematological alterations (erythrogram, white blood cell count, thrombogram, plasma glucose and total proteins). Therefore, 150mg/L of trichlorfon can be used in therapeutic baths to control and treat D.cycloancistrium infestations with no physiological impairments for arapaima.