Every week we will try and feature a parasite or disease that is important in our reefing world.
This is a serious group of diseases that is caused by flatworms termed monogeneans, (requiring only one host to complete their life cycle). Because they do not require a secondary host, they can rapidly increase their population in marine aquariums. They are often called “trematodes,” but they are actually not so closely related to digenean trematodes as once thought. Digeneans require two, or even three, hosts in order to complete their life cycle, so they rarely become a problem in marine aquariums where the required secondary host species are almost never present.
Digeneans either cause no visible symptoms, or the cysted state (called metacercaria) may cause white nodules under the fish’s skin or fins.
Monogenean worm of the genus’, that commonly infect marine aquarium fish, include Neobenedenia, Dactylogyrus, and Gyrodactylus. This week we will shift our focus on the Neobenedenia
Neobenedenia melleni (eye flukes)
These are relatively large (up to 8 mm), egg-laying worms that live on the skin or eyes.
Neobenedenia infections peak slowly, there may be no symptoms for weeks after you acquire a fish. Eventually, as the flukes multiply and grow in size, they begin to cause symptoms of the disease.
The first obvious symptom may be slightly cloudy eyes, caused by the transparent fluke feeding on the eye tissue and eliciting a tissue reaction. This gives this worm the common name of “eye fluke,” although it is unknown whether these worms actually prefer to feed on eye tissue, or whether that is just where they first become apparent.
As the infection becomes more serious, the fish will “flash” (scrape against objects in the tank), and their skin colour will become dull, their fins may become tattered, and they just generally get a “scruffy” look to them. Rapid breathing due to stress, possible secondary infection, and then death will follow if treatment is not begun.
The best means of diagnosis is to give the fish a five-minute freshwater dip. Not only does this knock back the infection by killing the adult parasites, but even a casual look at the bottom of the dip container afterwards will help to positively identify this disease. The worms turn an opaque, “whitish” colour and fall to the bottom.
Angelfishes and butterflyfishes are especially prone to Neobenedenia infections, so any of these fish that have been housed at an import facility that does not prophylactically treat for trematodes stand an increased chance of being infected.
Treatment
Many suggest using a freshwater dip as a treatment for all incoming fish. The two drawbacks to this is the dips are not 100% effective they do not harm fluke eggs.
Chemical Treatments
v Whole-tank formalin baths at 166 ppm will eliminate the adult flukes from an aquarium but not the eggs. Because this type of treatment has no residual effect, the treatment may need to be repeated every two weeks for two or three more times.
v A better alternative is a praziquantel treatment at 4 ppm, followed by a 50% water change after 48 hours, then a second treatment 12 to 14 days later, followed by another 50% water change 48 hours later.
Many home aquarists buy cleaner wrasses, neon gobies, or cleaner shrimp in the hope that these animals will clear their fish of parasites. This is simply never effective for bacterial or protozoan infections. However, with some large parasites, notably copepods and Neobenedenia, only partial control may be seen.
In our next feature we will be focusing on the Dactylogyrus genus.
Flatworms on Fish
Neobenedenia melleni (eye flukes)
Symptoms
Neobenedenia infections peak slowly, there may be no symptoms for weeks after you acquire a fish. Eventually, as the flukes multiply and grow in size, they begin to cause symptoms of the disease.
The first obvious symptom may be slightly cloudy eyes, caused by the transparent fluke feeding on the eye tissue and eliciting a tissue reaction. This gives this worm the common name of “eye fluke,” although it is unknown whether these worms actually prefer to feed on eye tissue, or whether that is just where they first become apparent.
As the infection becomes more serious, the fish will “flash” (scrape against objects in the tank), and their skin colour will become dull, their fins may become tattered, and they just generally get a “scruffy” look to them. Rapid breathing due to stress, possible secondary infection, and then death will follow if treatment is not begun.
Diagnosis
The best means of diagnosis is to give the fish a five-minute freshwater dip. Not only does this knock back the infection by killing the adult parasites, but even a casual look at the bottom of the dip container afterwards will help to positively identify this disease. The worms turn an opaque, “whitish” colour and fall to the bottom.
Treatment
Chemical Treatments
v A better alternative is a praziquantel treatment at 4 ppm, followed by a 50% water change after 48 hours, then a second treatment 12 to 14 days later, followed by another 50% water change 48 hours later.
