Killing effect of various treatments on the monogenean Heterobothrium okamotoi eggs and oncomiracidia and the ciliate Cryptocaryon irritans cysts and theronts

The effect of chlorine (12, 60, and 120 ppm available chlorine concentrations), benzalkonium chloride (100 ppm), freshwater, heat (40 °C), and drying on the hatching ability of Heterobothrium okamotoi eggs and Cryptocaryon irritans cysts was examined. The eggs and cysts at an early stage (1–16 h after spawning or leaving the host for H. okamotoi and C. irritans, respectively) and at a late stage (72–87 h) were exposed to each treatment for 1 or 24 h. Hatching of H. okamotoi eggs and C. irritans cysts was completely suppressed at both early and late stages when they were exposed to heat for 1 h. Exposure to chlorine at a concentration of more than 60 ppm available chlorine or to drying for 24 h was also effective in preventing hatching completely. However, freshwater had limited effect on preventing hatching of both parasites. Although benzalkonium chloride treatment for 1 h prevented hatching of C. irritans cysts completely, it was not effective against H. okamotoi eggs. One-hour treatments with chlorine (2.4 and 12 ppm) or benzalkonium chloride (100 ppm),or heat (40 °C) killed hatched H. okamotoi oncomiracidia and C. irritans theronts. These methods would be useful to prevent the horizontal infection with these parasites from used equipment, tanks, and wastewater in fish-rearing facilities.