In vivo evaluation of the antiparasitic effect and LC50 of the Talisay (Terminalia catappa) leaf extract against Ichthyophthirius multifiliis on Nile tilapa (Orecochomis niloticus)

Abstract

Ichthyophthirius multifiliis is a protozoan ecto parasite that causes debilitating damage and death to populations of freshwater fish worldwide. Common and persistent in tropical and temperate regions, it especially affects the ornamental fish trade and aquaculture industry – of which, a susceptible species of interest is the Nile tilapia (Oreochromis niloticus). Epizootic outbreaks in aquaculture of food fish raise concern with regards to chemical treatment, due to the possible accumulation of toxic chemicals in fish host tissue that may detrimentally affect consumers. This study aimed to determinethe effect of varying leaf extracts of a traditional Philippine medicinal plant locally called talisay (Terminalia catappa) on I. multifiliis infestation in Nile tilapia, and to determine the median lethal concentration (LC50) of the extract to the fish host. Nile tilapia fingerlings were infested using the cohabitation method (El-Dien & Abdel-Gaber, 2009)and were subsequently treated with 600 mg/L, 800 mg/L, 1,000 mg/L of aqueous talisay leaf extract. Methylene blue (1.32 mg/L) served as the positive control, while distilled water served as negative control. Deaths of fish and surviving I. multifiliis trophonts on host skin and fins were quantified within a 96-hour treatment period. The mean numberof surviving trophonts on dead tilapia for the 600 mg/L, 800 mg/L, and 1,000 mg/L, positive and negative control were 4.50, 4.00, 13.50, 4.25, and 90.00 respectively. One way ANOVA with Tukey’s post-hoc test showed that the mean number of surviving trophonts for all treatment groups (600 mg/L, 800 mg/L, 1,000 mg/L, +) and the negative control were significantly different (p = 0.007) – indicating that all experimental concentrations significantly reduced I. multifiliis infestation. Calculated antiparasiticefficacy values were 56.770% for 600 mg/L talisay, 77.814% for 800 mg/L talisay,xi 88.091% for 1,000 mg/L talisay, and 77.325% for the positive control. Extract concentrations appeared not to significantly contribute to tilapia mortality as no significant difference was found among all groups (p = 0.780); the calculated LC50 for the extract was 774.597 mg/L. The most cost-effective treatment determined to be at par with commercially-used methylene blue and that can be recommended as an alternative medication in aquaculture was the 600 mg/L talisay aqueous leaf extract.