Eliminating Saltwater Aquarium Skin Flukes – Part 1

Joe RowlettBy Joe Rowlett 3 months ago
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Dying Neobenedenia skin flukes on Pomacanthus navarchus. Credit: hakofucu

Dying Neobenedenia skin flukes on Pomacanthus navarchus. Credit: hakofucu

 One of the most frequently encountered parasites of marine aquarium fishes are skin flukes. You can find these insidious flatworms dining on the skin and mucous of wrasses, angelfishes, butterflyfishes, rabbitfishes, triggerfishes and many other groups—as a rule of thumb, the more money you spend on a fish, the more likely it is to have skin flukes. But, despite the ubiquity of this parasite at wholesalers and retailers, few aquarists make any real effort to keep this pest from entering their aquariums, and, once introduced, there is often conflicting information on how best to eradicate them. Rather than parroting the same advice, let’s take a closer look at what the scientific literature has to say on the matter. LIFE HISTORY  
Flukes on a Royal Gramma. Credit: Ostri/ReefCentral

Flukes on a Royal Gramma. Credit: Ostri/ReefCentral

 When we talk about skin flukes in the aquarium, we’re really only talking about one species—Neobenedenia melleni (though the synonym N. girellae is often used interchangeably). It was originally discovered when specimens began infecting fish at the New York Aquarium in the 1920’s, and, since then, it has been found on over 100 different hosts from more than 30 families, mostly from the perciform and tetraodontiform orders, but also including a soldierfish, a catfish, a garden eel, a mosquitofish and several scorpionfish relatives. With such a wide range of targets, this circumtropical species has become a major pest to commercial aquaculture. In a study of Caribbean surgeonfishes, anywhere from 10-100% of specimens showed the presence of Neobenedenia, with the highest rates coming from Blue Tang (A. coeruleus) collected in shallow bays. This is also a remarkably prolific worm, capable of self-inseminating in the absence of a mate and able to lay upwards of 500 eggs a day and more than 3000 in the course of its three-week lifespan. Thus, a single fluke introduced into an aquarium can quickly and easily start a sizable population. 
Neobenedenia on Purple Firefish. Credit: guinness0514/ReefCentral

Neobenedenia on Purple Firefish. Credit: guinness0514/ReefCentral

 Symptoms of infection include reduced feeding, lethargy, cloudy eyes, excessive mucus production and discolored or darkened skin. Since this parasite is mostly transparent, it is effectively invisible on the host fish until closely examined, and, unlike some parasites which target a specific part of their host, Neobenedenia has been found on all parts of the body, including the fins, gills, eyes and even the nasal cavities. Often the first indication of an infestation can be seen in the characteristic “flashing” behavior of infected fish, which manifests as erratic swimming and scratching against any firm structures as the unlucky fish attempts to scratch these irritants off its body.  
Neobenedenia skin fluke. Credit: University of Ottawa Biolabs

Neobenedenia skin fluke. Credit: University of Ottawa Biolabs

 If left to multiply, this parasite can quickly reproduce to plague proportions and is able to easily kill aquarium specimens that are susceptible to its wormy wrath. As far as treatment goes, there are three methods which warrant discussion: 1) biological controls, such as cleaner fishes and shrimps 2) altering water parameters, such as temperature and salinity 3) adding medications and supplements. Fortunately, there is a vast literature which has examined these variables in exquisite scientific detail, so, unlike so much aquarium hearsay, we can speak accurately as to what works and what doesn’t for eliminating Neobenedenia. In part 2 of this discussion, we will explore these treatment methods in detail…

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Joe Rowlett
About

 Joe Rowlett

  (199 articles)

Joe is classically trained in the zoological arts and sciences, with a particular focus on the esoterica of invertebrate taxonomy and evolution. He’s written for several aquarium publications and published the first exhaustive phylogenies for a number of reef fishes. For many years, he lorded over the marinelife at Chicago’s venerable Old Town Aquarium. His one true love is entomology, and he has most recently studied prairie insect ecology at the Field Museum of Natural History. When he’s not busy penning recondite fish missives or staring through a microscope at fly genitals, he can usually be found fawning over his malicious and spiteful kitty cat.