Colorni (1985) successfully achieved the total eradication of Cryptocaryon irritans by switching fish between two aquaria every three days for four switches in total.

The Method

This method requires two aquaria suitable for holding the fish to be treated. The aquaria can have water with normal salinity and the temperature should be close to 25°C. The infected fish are kept in the first aquarium and after exactly three days they are moved to the second aquarium. The first aquarium is emptied, cleaned and allowed to dry for at least 24 hours. The first aquarium should then be set up again ready to hold the fish again. After the fish have been in the second aquarium for exactly three days they are moved back to the first aquarium. The second aquarium is emptied, cleaned and allowed to dry. This process should be repeated until the fish are returned to the first aquaria for the third time. At this time there will be no surviving parasites.

Why does this method work?

This method works because the trophonts stay attached to the fish for at least 78 hours (Burgess and Matthews, 1994) and no more than 7 days (Colorni, 1985; Yoshinaga and Dickerson, 1994; Diggles and Lester, 1996) and the reproduction by the tomonts takes at least 84 hours (Burgess and Matthews, 1994) all at or around 25°C. While the fish are in the first aquarium for the first time they will be infected with trophonts. When they are moved to the second aquarium they trophonts will go with them but any tomonts will be left behind. Any trophonts that drop off during their time in the second aquarium will not complete reproduction before the fish are moved back to the first aquarium. There may still be some trophonts attached to the fish when they are transferred back to the first aquarium, but again if these drop off they will not complete reproduction before the next transfer. By the time the fish reach the second aquarium for the second time, nine days will have passed all the trophonts that were originally attached will have dropped off and have been left behind to die in the cleaning process. The fish will not have been able to become reinfected because they were moved each time before reproduction was completed.

What is required for cleaning?

Hirazawa et al. (2003) found that drying for 24 hours was sufficient to kill all tomonts regardless of their stage of development. Cleaning of the aquarium between transfers can be as simple as hosing the tank out, although wiping with a light scourer wouldn't hurt. What is important is to ensure that the tank is dried thoroughly and left dry for at least 24 hours. Blowing with a small fan heater or hair dryer may assist the drying process and additionally will kill the tomonts as Hirazawa et al. (2003) also found that heat (40°C) for 1 hour was sufficient to kill all tomonts.

Other considerations

One difficulty with this treatment keeping up the water quality in the aquaria during the course of the treatment. While initially, each of the aquaria may have established biological filters, these will need to be cleaned and dried after the first use to kill any tomonts present. For the subsequent transfers to each aquarium, there will be no biological filtration present. One way to overcome this would be to move some filtration media from another aquarium which is known not to have Cryptocaryon present. Another option would be to do frequent water changes to remove pollutants.

It should be noted that catching and moving the fish every three days could be quite stressful.


Burgess P.J. and Matthews R.A. 1994. A standardized method for the in vivo maintenance of Cryptocaryon irritans (Ciliophora) using the grey mullet Chelon labrosus as an experimental host. J Parasitol 80:288-292.

Colorni A. 1985. Aspects of the biology of Cryptocaryon irritans, and hyposalinity as a control measure in cultured gilt-head sea bream Sparus aurata. Dis. Aquat. Org. 1:19-22.

Diggles B.K. and Lester R.J. 1996. Influence of temperature and host species on the development of Cryptocaryon irritans. J Parasitol 82:45-51.

Hirazawa N., Goto T. and Shirasu K. 2003. Killing effect of various treatments on the monogenean Heterobothrium okamotoi eggs and oncomiracidia and the ciliate Cryptocaryon irritans cysts and theronts. Aquaculture 223:1-13.

Yoshinaga T. and Dickerson H.W. 1994. Laboratory propagation of Cryptocaryon irritans Brown, 1951 on saltwater-adapted black mollies Poecilia latipinna. J. Aquat. Anim. Health 6:197-201.

Last updated: April 25, 2005