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Pest Flatworms (aka "Planaria") & Marine Aquariums

By Anthony Calfo 

Flatworms on a Corallimorph

Red Flatworms Hello to the WWM crew, <Cheers, Martha. Anthony Calfo in your service> I need some advice about ridding my tank of a red flatworm invasion.  <a common problem> I have a 75 gallon reef. 5" DSB with 110lbs of live rock. I have LPS only and 1400gph for circulation being moved about by two sea swirls, giving the tank quite turbulent waters, IMO.  <but are the worms mostly in the lesser current areas? They do hate strong water flow> I have a 20 gallon refugium and use an AquaC EV180 skimmer. Ammonia & Nitrites 0, nitrates 10ppm, ph 8.4 (average) SG 1.024, temp 81 degrees. I have a calcium reactor that keeps a consistent reading of Ca 440, and Alk 11dkh. <all outstanding> This flatworm population has taken over my tank. It is all over the live rocks, on the sand bed and has attached to my two candy canes and open brains. It is really starting to worry me.  <no reflection of tank health or husbandry... just one of those things> At first it was just an eye sore, but now it seems to be out of hand. Is there any known way of ridding a tank of these creatures, or are they here to stay? <no...in fact, they often wax (hard) and wane (suddenly) on their own.> If you have any information on these pests I would love to read about it. Thanks for your time. Martha P.S. I have enclosed two pictures of these flatworms <no easy solution Martha... aggressive skimming, very strong water flow, perhaps a natural predator (if tankmates allow) and time usually take care of the matter... even if it takes a couple of months. The following is an excerpt from my Book of Coral Propagation, Vol. 1 on these so-called "Rust-Brown Planaria": "Rust Brown Planarians are just one such example of a nuisance organism that needs to be monitored if not controlled. This flatworm is usually 1/8 to ?" in size (~3-6mm) with a color ranging from orange through red to brown. It is cited in aquarium literature as Convolutriloba retrogemma and considered to be a pest because it can expand in population to plague proportions in a matter of a few short months. Populations get so dense that they occur in crowded mats that literally block necessary sunlight and circulatory functions from the corals that are forced to serve as perches for them. They are said to ingest zooxanthellae from decaying coral tissue and prosper under bright illumination. They dislike strong water flow and are often noticed in the areas of weakest water movement in an infected display. Increased water movement alone in otherwise properly maintained aquariums can sometimes reduce the population of flatworms.  Aggressive protein skimming also helps to control the population of this annoying pest. It has also been demonstrated that low salinity impedes the growth of flatworm populations but at the expense of other desirable invertebrates in the display if applied as a long bath. I once inadvertently dropped the salinity of a badly infected system from 1.023 to 1.017 with a water exchange using water that I thought was salted… but was not. The sharp drop in salinity promptly killed every discernible flatworm in the display, but shocked every Sinularia into expelling zooxanthellae at the same time! The leather corals took months to recover and I would never recommend imposing such shock deliberately. Indeed, short freshwater baths are effective against many Planaria, but quite stressful to other desirable coral and invertebrates even on selectively treated rocks.  Natural predation may help but is somewhat unpredictable. Dragonets (Synchiropus species) and Leopard wrasses (Macropharyngodon species) have been used with varying degrees of success. Both fishes are truly in need of care by advanced aquarists. Leopard wrasses and dragonets will survive very well in systems with refugiums generating copious amounts of zooplankton as well. Chelidonura species of sea slugs have also been cited as excellent natural predators, but acquiring an effective species is difficult for many livestock resellers, as collectors often lump various Nudibranchs into an assorted category. The result is that numerous species of sea slugs unsuitable for captivity get imported in an effort to acquire just one that eats this species of flatworm.  Manual siphoning is moderately effective but laborious. The truth of the matter is that such flatworms are common and present in many tanks. They will wax and wane and rarely linger in a large sustainable population. If a system is aggressively scrubbed with a protein skimmer, properly fed and not overstocked, the colony of pest flatworms will most likely crash within a couple of months. Support in the meantime through occasional siphoning, increased water flow and a natural predator (if it is suitable for the system and tank mates) is likely to make this frighteningly unpleasant symptom a truly small concern." Anthony Calfo... with kind regards. <Anthony, would you mind if I place this as "an article" (on its own page with links) on WWM? It's excellent and complete... something we can point folks to... Bob F> <<Bob, please do and thanks. I'll shape it up a little if you like so that it stands alone a little better. Before or after posting... your call. <Actually... yours. Will post as is... and if you'd like it modified... go to it!> Hey... how about forgetting the tee-shirt when you come back from Oz and bring us a box of Gemmatum tangs...hehe! <Wrong sub-continent my friend. Now, we are planning on getting out to Reunion and Mauritius next year... Interested in the trip? Bob F> Antoine>> 

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