Validation of a rapid counting method for assessing treatment efficacy against Lepidotrema bidyana infecting silver perch Bidyanus bidyanus

We used a published sub-sampling method for estimating the abundance of the monogenean Lepidotrema bidyana, a gill parasite of silver perch Bidyanus bidyanus, and determined that it also accurately predicts parasite abundance post-treatment. Post-treatment parasite abundance estimates based on the number of parasites on the first left posterior hemibranch were compared to actual counts on fish after bath and oral treatment trials with praziquantel and fenbendazole. Post-treatment parasite abundance estimates were significantly correlated to real counts of all individual hemibranchs, accurately predicting the parasite abundance on an individual host. There was no significant difference in the post-treatment parasite abundance between individual hemibranchs, however, indicating that the treatment affected L. bidyana abundance on each hemibranch unequally. Use of this method is ineffective at predicting post-treatment abundance; however, it accurately predicts the remaining parasite abundance, aiding evaluation of treatment efficacy, while reducing post-treatment sampling time or facilitating larger sample sizes.