Scientists have reported progress in the development of a vaccine for whitespot disease, caused by the parasite Ichthyophthirius (commonly known as Ich).
Researchers from the US Agricultural Research Service (ARS) found that when Channel catfish were injected with a potential vaccine, the fish responded by producing protective antibodies against Ich and were able to survive the infection.
Ich is a single-celled protozoan parasite that has a multi-stage life cycle. The vaccine was created by using parasites from the infective stage of the cycle, during which they are known as trophonts. The trophonts burrow into the skin, fins and gills of freshwater fish, and are responsible for causing the white spots associated with the disease. The researchers used high-frequency sound waves to kill the trophonts before injecting them into catfish.
The research was presented at a recent meeting of the American Chemical Society (ACS). One of the scientists, Dr Dehai Xu, said: "Outbreaks of the parasitic disease caused by Ich can result in losses of 50–100% of fish. The disease is very common and almost every home fish hobbyist has encountered it."
Whitespot is one of the most common infections in freshwater fish and causes problems for fish farms, public aquariums, aquatic retail outlets and home aquariums. It is usually treated with a formaldehyde solution.
Dr Xu added: "To vaccinate against Ich, you would need much less medication and it would not pose an apparent threat to the environment. You would need just one treatment to make the fish immune for life."
Before a commercial vaccine can be developed, Dr Xu noted that a number of problems would need to be overcome. Importantly, instead of using injections to vaccinate individual fish, the vaccine would need to be formulated for administration either in food or directly to the aquarium water.