The influence of water temperature on the life-cycle of Sparicotyle chrysophrii (Monogenea: Microcotylidae), a common parasite in gilthead seabream aquaculture

The efficient control of harmful parasites, such as monogeneans, is essential in aquaculture and requires an understanding of their transmission in changing environments. This study evaluated the effect of temperature on the transmission and development of Sparicotyle chrysophrii, a pathogenic monogenean commonly found in gilthead seabream (Sparus aurata) farmed in the Western Mediterranean. The effects of temperature on post-larval development, infection success and post-infection survival of S. chrysophrii were assessed experimentally. The infection success was maximal at 18 °C and 22 °C but declined at 14 °C and 26 °C, suggesting that newly settled parasites will be abundant at 18 °C–22 °C and transmission will be less successful outside this temperature range. Temperature also affects parasite survival after host invasion: S. chrysophrii survival to maturity is highest at 22 °C but substantially lower at 18 °C and is the lowest at 26 °C. Sparicotyle chrysophrii can complete its life-cycle from 14 °C–26 °C in the Western Mediterranean, but both the incubation period and time to maturity extend as temperature rises and thus, generation time increases from 26 to 51 days. Parasite abundance is predicted to increase rapidly at 22 °C and, therefore, S. chrysophrii is more likely to become pathogenic at this temperature, although severe infections can occur between 18 °C and 22 °C according to the high infection success. Biological data can be used to assess strategic timing for treatment applications. The first treatment removes all life-history stages except for the eggs. Thereafter, the maximum incubation period and the minimum time to maturity allow for designing treatment windows for the application of subsequent treatments to strategically manage S. chrysophrii; 8–14 days at 26 °C, 9-21 days at 22 °C, 11–28 days at 18 °C and 14–35 days at 14 °C. The external infective pressure as well as the generation time and survival to maturity, the best combination of both parameters at 22 °C, will determine the infection progression.