At least 15 Gyrodactylus species have been reported from tilapia of which two species, G. cichlidarum and G. yacatli are widely distributed and often associated with aquaculture mortalities. This study aimed to validate a sensitive method for targeted surveillance and early detection of Gyrodactylus species in farmed and wild tilapia. The specific objectives of the trial were to evaluate the efficacy of a non-lethal Gyrodactylus parasite collection method using a hydrogen peroxide treatment, against a lethal 2-phenoxyethanol treatment, and to evaluate the time and resource requirements of the two techniques. The trial sampled 60 fish, based on an expected mean parasite prevalence of 20% in farmed and wild populations. Live fish were placed individually in a funnel with 1000 ml of a 560-ppm hydrogen peroxide solution for 3 minutes. For euthanasia, 2-phenoxyethanol was incrementally increased from a sedative to a lethal dose (0.15 mL/L to 1.2 mL/L). After exposure, the fish were removed, and the collected parasites were filtered and stored in 100% ethanol for further morphological and molecular characterization. Data were visualized graphically and statistically analyzed using Analysis of Variance (ANOVA), t-tests, or non-parametric methods. The detection sensitivity was evaluated by calculating the likelihood of finding at least one parasite per infected fish. Time and cost requirements were documented to assess the relative efficiency and resource demands of the two techniques.
Key words: Evaluation, Non-Lethal, Gyrodactylus, Surveillance, Tilapia