'Pasteurised' Tilapia: Drastic Mortality of Gyrodactylus cichlidarum During the Spring 2024 Heat Wave.

During spring 2024, a heat wave induced sustained water temperatures of 34°C during a week in Veracruz, Mexico. Serendipitously, we monitored Gyrodactylus cichlidarum infecting farmed tilapia fry during this pulse warming event and recorded a drastic decline of parasite populations over the following days. We subsequently established that parasites incubated in vitro at ca. 27°C survived up to 24 h, while at ca. 30°C and 34°C, all worms died within 4-7 h. Abnormal haptor structures were observed in parasites that developed and were born at a water temperature of 34°C. Under farming conditions, no unusual fish mortality was recorded, suggesting that pulse heat treatment may be an effective method to control G. cichlidarum, a recognised tilapia pathogen.