A novel treatment against the monogenean parasite, Gyrodactylus turnbulii, infecting guppies (Poecilia reticulata), using a plant-based commercial insecticide Timor C

Monogenean infections are a common cause of fish morbidity and mortality in aquaculture. In most cases, treatment relies on the application of toxic or unapproved chemicals. Therefore, alternative treatments against monogenean infections in fish that are safe and environmentally friendly are needed. In the present study, the efficiency of Timor C, a plant-based commercial insecticide, was investigated against Gyrodactylus turnbulii, a monogenean parasite infecting guppies (Poecilia reticulata). Since G. turnbulii primarily infects the fins and skin, with a predilection for the caudal fin, tail clips of heavily parasitized guppies were exposed in vitro to Timor C at various concentrations and parasite detachment and death were recorded over time. There was a positive correlation between time to detachment and Timor C concentration, with complete detachment within 60 min of exposure at a concentration of 50 ppm. Withdrawal of Timor C afterward did not lead to recovery of the exposed parasites. Treatment of infected fish for 24 h at 10 and 20 ppm was effective in lab-based trials, reducing the infection prevalence from 100% at time 0 to 22% post-treatment, and the infection rate to an average of less than one parasite per fish, as compared to an average of about five parasites per fish in the control. Repeated weekly treatment application for three consecutive weeks appeared safe for the fish, and did not cause an adverse effect to the biofiltration system, as determined by examining nitrification activity, compared to non-treated controls. Treatment was successfully tested in three separate applications at a commercial closed recirculating guppy farm, where a significant reduction in infection rates was achieved. Timor C was not toxic to Artemia at concentrations ranging from 10 to 100 ppm over 24 h of exposure. This study demonstrates the effectiveness of Timor C as a treatment against G. turnbulii infection in guppies and potentially against similar parasites in other aquacultural species.