Efficacy of garlic based treatments against monogenean parasites infecting the guppy (Poecilia reticulata (Peters))

Abstract

Monogenean infections of commercially farmed fishes are responsible for significant economic losses. Garlic (Allium sativum) is a well-known spice which also possesses anti-microbial and anti-parasitical properties. The current work aimed to test the efficacy of garlic-based treatments against infection with monogenean sp. in the guppy (Poecilia reticulata). Clipped sections of tail fins of guppies heavily infected withGyrodactylus turnbulliwere exposed to aqueous garlic extract (7.5 to 30mLL−1) and visually observed under a dissecting microscope. Results revealed that exposure to garlic caused detachment of parasite and cessation of movement indicating death. A positive correlation was seen between garlic concentration and time to detachment and death of parasites, which, at the highest concentration of 30mLL−1, occurred at 4.1 and 8.6min, respectively. Bathing in aqueous garlic extract (7.5 and 12.5mLL−1) was tested in guppies infected withG. turnbulli. Prior acute toxicity tests revealed the maximum tolerance levels of guppies to garlic extract to be 12.5mLL−1for 1h. Bathing of infected fish in garlic extract (7.5 and 12.5mLL−1) significantly (p<0.05) reduced infection prevalence and intensity as compared to the control. Oral treatments using dry garlic powder-supplemented diet were tested on guppies infected withG. turnbulliandDactylogyrussp. Fish were fed with food containing 10% and 20% dry garlic powder for 14 days. Groups fed with garlic supplemented diets showed significantly reduced (p<0.05) mean prevalence and mean intensity of parasites as compared to the control. Dietary application of garlic did not appear to affect palatability. Fresh crushed garlic was added at a level of 1gL−1and applied as an indefinite bath for 14 days. This treatment was seen to significantly reduce (p<0.05) parasite prevalence and mean intensity as compared to the control. Histopathology revealed elevated muscular dystrophy in the 20% garlic-fed group, as compared to control. These findings demonstrate the potential of garlic as a natural alternative to currently used chemical treatments formonogeneansp. infection in the guppy.