Water temperature affects Cryptocaryon irritans development, cryptocaryoniasis occurrence and an auxiliary treatment decision-making webpage

Abstract

Cryptocaryon irritans is the causative pathogen of “white spot disease” of marine teleosts, and its development and pathogenicity are affected by the seawater environment. This study conducted a total of 7 water temperature gradients (15 °C, 18 °C, 21 °C, 24 °C, 27 °C, 30 °C, and 33 °C) to compare encysting, cleaving, hatching, number and shape, and infectivity of C. irritans to fish (large yellow croaker, Larimichthys crocea). The protomonts in the treatment groups at 15 and 18 °C could quickly encyst within 1 h, which were significantly faster than those of the 21–33 °C groups. At 15–21 °C, the starting time for the tomonts to cleave lagged behind that of the 24–33 °C groups. During the 14-d treatment, the cleavage rate of tomonts in each group at 15–33 °C increased with the treatment time, but the final cleavage rates of the 15 and 18 °C groups were only 43.67% and 61.44%, respectively, which were significantly lower than those of other groups at 21–33 °C. While the hatching rates of the tomonts in the 18–33 °C groups increased with the prolongation of the treatment time, and the highest and lowest values appeared at 27 and 18 °C, respectively. However, the tomonts in the 15 °C group did not hatch theronts until the end of the experiment. The maximum and minimum numbers of hatched theronts appeared at 30 °C and 18 °C, respectively. Increasing or decreasing the temperature from 27 °C would make the parasites slender and smaller at low temperatures treatment. The infectivity of theronts hatched at 18 °C was significantly lower than that of theronts hatched at 27 °C and 33 °C. We built an auxiliary treatment decision-making webpage for this parasitosis based on temperature, salinity, and pH.