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As its name suggests, guppy disease (Tetrahymena) is a major problem for those keeping guppies, but other types
of fish can be affected too.
As its name suggests, guppy disease is a major problem for those keeping guppies, but other types of fish can be affectedtoo.
IdentificationGuppy disease resembles ich, aka whitespot disease, (Ichthyophthirius multifiliis) in many ways, and positive identification isimpossible without microscopic analysis. Affected fish are usually (but not always) covered with white spot-like cysts on theirflanks and fins, and also exhibit such symptoms as heavy breathing, lethargy and clamped fins. Swellings may develop inthe muscles of the fish. Grey patches of mucous may be apparent, particularly on dark-colored fish such as black mollies.
Note that despite the name, guppy disease can affect a variety of fish including cichlids, catfish and tetras. But with thatsaid, guppies and their close relatives such as mollies and Limia spp. do seem particularly sensitive to the parasite.Clickimage to enlarge As its name suggests, guppy disease is a major problem for those keeping guppies, but other types of fish can be affectedtoo.
Compared to ich, guppy disease causes death much more quickly. In some cases an infected guppy can appear healthyone day and be dead the next. Besides the limited time available for diagnosis, medications that work against ich or velvettend to work poorly, if at all, against guppy disease.
PathologyThe pathogens that causes guppy disease are ciliate protozoans in the genus Tetrahymena including Tetrahymena corlissiand Tetrahymena pyriformis. Interestingly, Tetrahymena are not obligate parasites, and likely exist in most aquaria withoutcausing harm. They may even be commensals, roving across the surfaces of fish consuming whatever organic matter theyfind. Only under certain circumstances do they invade the tissues of their hosts and cause harm, typically via lesions andvery likely in situations where poor diet, stress, and/or poor environmental conditions have weakened the fish’s immunesystem.
Life CycleTetrahymena have a life cycle similar to those of other ciliates, alternating between stages that multiply vegetatively throughcell division and sexually through conjugation and exchange of genetic material between cells. Unlike the ich parasitethough, Tetrahymena don’t need a host to complete their life cycle. As a result they can live for years in an aquarium withoutcausing disease, only to suddenly become problematic should conditions in the aquarium deteriorate or the fish beingmaintained become stressed or damaged.
TreatmentUnfortunately, there are no easy, reliable treatments for guppy disease. Under laboratory conditions niclosamide,albendazole and chloraquine have all been found to provide some degree of relief, but these have not been turned intomedicines that aquarists can use. Some success has been had using multipurpose anti-protozoan medications such asClout, but several treatments may need to be performed alongside significant improvements in diet and environmentalconditions.
SaltThose Tetrahymena species that affect freshwater fish are more tolerant of salinity than ich parasites, so the slight salinityused to treat ich won’t work against guppy disease.
PreventionGuppy disease is best managed through prevention. This will be a three-fold process starting with careful selection of newlivestock. Among commonly traded aquarium fish guppies are particularly affected by Tetrahymena infections and it isabsolutely crucial that the aquarist selects healthy livestock from aquariums with no sickly fish. Bear in mind that theparasites can be carried by other fish even if they don’t become sick from them, so buying some Corydoras catfish from anaquarium that contains sick guppies is just as likely to introduce the disease to your aquarium as buying the guppies themselves. Check that your retailer is doing all the usual things to prevent infections spreading among fish andbetween aquariums, such as removing sick fish promptly and using disinfectant to clean fish nets between uses.
The second step required to limit problems with guppy disease is to quarantine and observe all new livestock. This is goodpractice anyway, and holding new fish in a quarantine aquarium for 4 to 6 weeks before moving them to the main aquariumshould make it easier to detect and treat all sorts of diseases, not just Tetrahymena infections.
Finally, fish need to be maintained under healthy conditions. In the case of guppies this includes providing them with aspacious fish aquarium (at least 15 US gallons) and good water quality (i.e., zero ammonia and nitrite). Water chemistrymust be hard and alkaline; aim for at least 10 degrees dH, pH 7.5 to 8.5. Brackish water conditions aren’t essential but theydo seem to help with guppies, Limia and especially mollies. Male guppies are notoriously aggressive, and any physicaldamage they cause can trigger guppy disease infections. Maintain groups of at least two females per male, and use floatingplants such as Indian fern to create hiding places at the surface of the fish aquarium. Needless to say, any other fish thatdamage guppies through aggression or fin-nipping are just as likely to create lesions through which Tetrahymena infectionscan get started.
Neale Monks studied zoology at the University of Aberdeen in the north of Scotland and obtained his Ph.D. at the NaturalHistory Museum in London. He's also been a marine biologist, a high school teacher, a university professor and a museumsexhibit designer. But his real love has always been tropical fish. His particular interest in brackish water fish culminated inhis editing of the first encyclopaedic book on the topic, 'Brackish-Water Fishes', published by TFH in 2007. Neale regularlycontributes to all the major English-language fishkeeping magazines, focusing especially on community tanks, biotopes,healthcare and water chemistry issues. After living in London and then for a while in Lincoln, Nebraska, Neale now lives in aquaint cottage in a pretty market town in Hertfordshire, England, where he divides his time between teaching and writing.

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