Isopod options, please help     9/25/17 Hi guys, You have been so helpful over the years, I hope everyone is well and you can help me with this too. I have a young Kole tang in my QT. He was purchased 2 weeks ago and doing great, feeding, active, good colours, etc. He does however seem to have a small lump on his back fin, right at the tip and this has grown a bit over the past week. It is definitely not lymph or Ick. It looks like a small isopod although I can’t see eyes (yet!). It’s hard to take a good picture of it but I’m pretty sure that’s what it is although it hasn’t moved at all for the past 12 days. It looks like a grain of rice, only maybe ¼ - ½ of the size. <Mmm, okay> My question is what is the best way to remove it? <IF it's only the one, I would try carefully netting (use two, one in either hand, to manipulate the animal, rather than chase it), hold the fish near the surface of the water (watch out for the tangs on the caudal peduncle! They are sharp, and the fish knows how to wield them), and daub (with a cotton swab) full strength (37%) formaldehyde directly on the object. See WWM re Formaldehyde use, sourcing> I don’t know if I should dose Cupramine in the hope it would kill the parasite? <Mmm; no... not copper product/s. Will kill the host, much else before killing isopods> Manual removal would be easy as it’s just on his fin but hubby is not keen on getting the fish out of water to perform this. I have never had to perform FW dip and this scares me but is this also an option? <I would not pull on this spot just yet. IF it is an isopod, it will be VERY well attached and you will damage the fish. Better to poison/kill it as I've mentioned above, and have it drop off on its own> Many thanks and hope to hear from you soon. Jo <Please do report back your further observations. Bob Fenner> Re: Isopod options, please help     9/26/17 Thank you so much for your fast response, Bob! Yes, it is just the one and it hasn’t moved. <Okay!> Ok, I will look into sourcing the formaldehyde now. I have a bottle of Seachem’s Paraguard too, not sure if that will be any good. <Not useful here> I dosed the recommended amount of this broad spectrum treatment but the parasite seems perfectly happy still. Just one more thing regarding manual removal. The parasite is attached to the very tip of the tang’s back fin so I was thinking of perhaps cutting this tiny bit off? <Mmm... as an alternative, I'd try squishing it with strong tweezers and just pulling here> It will be no worse than having a nipped fin and I believe it will regrow. What do you think? As I said, it’s right on the very end. <An unusual position for a parasitic isopod... they tend to attach on the body, in the mouth, at fin insertions... where they can rasp, suck up tissue> I am attaching a picture which doesn’t show the parasite in detail but shows the position of it. ( I tried 3 different cameras including a DSLR but due to the fish’s colour, it’s impossible to focus on it well and he is a bit jumpy so I can’t get super close). <Can't really make out; but thanks for sending along> Thanks again Jo <Welcome. BobF>

crop

Re: Isopod options, please help    9/26/17 Yes, I was just thinking that the fin is probably not the best place for it but it makes it a bit easier to remove. I seems a tiny bit bigger today but again, after spending 30 min.s by the tank, I've given up trying to take a picture! Will keep you posted Thanks again <If possible; please do send along better resolved pic/s. B> Re: Isopod options, please help    9/26/17 Hopefully the next picture I send will be of the little beast removed from my beautiful tang! Watch this space, feeling determined! <Ahh, tres bien!> I had a flame angel in the QT too but after having observed it for 2 weeks (wasn’t brave enough to copper it), I decided to cut the quarantine short and move him over as I didn’t want that thing to move or drop off and start multiplying (don’t know much about them as have never come one across!). Angel has made himself at home in the DT and not taking orders from any of the old inhabitants, not even my 11 year old veteran Sixline! Thanks again Jo <Welcome Jo. BobF>

Isopod parasite      11/29/13
I have just removed a half inch isopod from the buccal cavity of my forktail
blenny. They blenny was suffering from swelling in the area and labored breathing and so my LFS suggested a freshwater dip as a last resort to see what was wrong. The copper and Prazi-pro I had previously tried treating this fish with seem to have little effect as the "lump" (now confirmed as an isopod) continued to grow. To my horror this giant (compared to the fish) thing tried backing its way out my fishes gills during the dip.
Sadly it was too large for this and became jammed in. I was forced to extract it with tweezers in an attempt to allow the fish to breath. The fish survived the initial removal but was either too stressed or had too much gill damage. He is now barley hanging on and I don't believe he will survive. I am  very concerned about my other fish. Everything I am reading is either about external isopod parasites or the one that eats the tongue. I am hoping one of the crew may know more about this buccal cavity isopod and what I should do to spare my other fish from this horrible ordeal.
<Nothing really>
I am not even sure if they are infected or if this was a one time thing but I do not want to lose any more fish.
 A very sad and horrified,
         Jen
<Buccal cavities are not strange places for some isopod parasites... great placement for water movement, protection from predators and foods! Due to their life cycle requirements there is not much chance that others are inhabiting or likely to infest your other fishes. Bob Fenner>
Re: Isopod parasite      11/30/13
Thank-you very much. I tried to find out more about what type of isopod this was but quickly found out that classifying these creatures takes a lifetime of study.
<Classifying perhaps; but identification not a big deal...>
 The best I could do is that it is from the family of Aegid. I will be replacing my blenny with a captive bred individual so that
I don't have to deal with the chance of another one of these coming in with a wild caught fish.
  Jen
<Yes; BobF>

Parasite on ocellaris?   3/18/13 Can you help me Id the rider on my ocellaris?  It looks like an isopod, <It is indeed>  but I've never had a problem before but just added pods from a reputable company on Thursday and today I found this.  They said they have never had an issue before.  The ocellaris have been in the tank over a month and were fully quarantined before adding to the display.  I can try to get him out but will be hard.  Any guidance would be appreciated. Mike <Easy to remedy... I'd likely catch/net the Clown and remove the one via forceps, or twixt your thumb and finger-nail. No other treatment likely necessary. See WWM re Isopods for more. Bob Fenner>

Re: Parasite on ocellaris?   3/18/13 Thanks!  Now for ocellaris hunting.... <Ah, good hunting! BobF>

Hitchhiking Cirolanid Isopods   8/24/10 Well, seems as though I noticed the first signs of life buzzing around in my water column last night after adding 30lbs of Vanuatu LR to the system this weekend. Unfortunately I am all but certain they are Cirolanid Isopods. I know folks mis-ID these quite often but I have read hours this evening (Shimek, Plankis, Melev) and feel pretty certain about the ID. So, on to the question. I am setting up this 40G breeder/30G Sump, this is the initial LR I am curing the system with, and plan to let it sit in the dark from now until New Years to seed itself. That's four months give or take a week or two, is this going to be long enough to starve the little buggers out? <I'd poison them... with a "medication" for killing arthropods/crustaceans... Read here re: http://wetwebmedia.com/crustdisfaqs1.htm and the Related FAQs file above: Isopods> Should I bother trying to nuke and pave or trap them since the system will be without fish for so long? Should I go longer than four months? Thanks so much for giving this a read, these little punks have me fairly stressed out. Don't want my new system to get off to a bad start. My Best, Bush Williams <Bob Fenner> Re: Hitchhiking Cirolanid Isopods 8/24/10 Thanks Bob, I added some high res photos at this link if your interested or would like to use them on WWM. http://www.reefcentral.com/forums/showthread.php?t=1896304 /Bush Williams (iPad) <Will do so, with credit to you. BobF>

U.S. dime at right

Munnid problem?   3/22/10
I seem to have had a population explosion of Munnids.
<No fun>
I'm keeping a purely crustacean, snail, polyp and mushroom based tank.
I have noticed that the Munnids seem to be converging around the polyps and possibly eating them - could this be true? or are they eating polyps that are dying off a little?
<Mmm, some Munnid Isopod species are predaceous, others detritivorous>
Should I introduce a scooter or some other fish?
<I would try to at least limit their numbers>
Thanks in advance
Mark Beharrell
<Welcome. Bob Fenner>

Re: Munnid problem?  3/22/10
Thanks for the reply. I will look into measures to combat them.
<Good>
Until I can get to the shop I'm dunking the rocks they most seem to congregate on in fresh RO water. They do seem to fall off but the population is too high to have any lasting effect.
<Yes... I suggest testing, devising food-traps to periodically (weekly likely) bait out and remove a good percentage of them/these. BobF>

Creature from movie" Alien" has got my pajama cardinal! Guys, woke up today to find this creature, isopod I guess, clamped on the face, mouth, of my cardinal. Did not look like the poor fish could open his mouth, just like in the Alien movie. Tried to catch fish but impossible in 450 reef tank. Worried these monsters could get out of control, only seen one though. Does any type of fish eat these things? <Not really. Good idea to get/use a fish trap (these are sold in the pet-fish industry (there's an ad in FAMA currently...) or from large warehouse stores (they're the same plastic traps for small rodents, but no fish sticker...> I recently moved a few pieces of rock from refugium to main tank and assume that is how this thing got into main tank. It is quite large, over 1/4 inch. Thanks, Paul <Maybe... bizarre. Catch the host, remove and toss. Bob Fenner>

I have a powder brown tang which has picked up a quarter of an inch long light brown crustacean on its anal fin. The bug looks kind of like a terrestrial rolly poly or pill bug. Also this thing seems to be pinching the fin. I already have a cleaner wrasse and shrimp. Do you know what this thing is and if and how I should get rid of it?  I bought your book this weekend and there the bug was right on page 148.  Also I have a white faced tang and I now feel pretty bad about buying that cleaner wrasse. Anyway the copepod disappeared after about 8 hours so I assume the cleaners got it. I am glad I bought your book. It answered a lot of questions and gave me a lot of ideas. Thanks for your time and Ill investigate further before submitting a question. Everett West >> Yes, this is a parasitic isopod... an aquatic type of rolly poly... and it is best to remove it by catching the fish and prising it off with a stout tweezers... Get ready and at the same time, daub a little mercurochrome or Merthiolate on the remaining sore with a "q-tip"... Bob Fenner

Isolating Isopods Hi JasonC, Good job filling in for Bob. <<why thank you... >> Can you give me some advice. I have a Sailfin tang with a parasite hanging on to its bottom fin. I'm pretty sure the parasite came in on a piece of liverock, but regardless its there. The thing looks like a white worm. Maybe 1/16 of a inch long and 1/32 of an inch thick. Pretty small but large enough to see some features on the parasite. I first noticed it about 2 weeks ago, and since it has doubled in size. There is now a small hole developing in the fin where the things mouth is. The tang does not show any signs that he is distressed yet, but I am afraid of letting this thing get to big, or if it reproduces god help me. I have a cleaner shrimp that cleans the tang from time to time, but the shrimp never touches this fin. I waited these two weeks hoping the shrimp would get it, but to no avail. Do you suggest a neon goby or cleaner wrasse to be added to the tank? If I could catch the tang (yeah right), would a fresh water dip be a better option? Would scraping it off with my nail work again if I could catch the tang. Last night I did notice 2 tiny white dots on another fin. I'm afraid these are small versions of the same parasite. <<Two courses of action here that I can think of, and both will require you to catch the fish. You can either manually remove the isopod, either with your fingers or tweezers OR freshwater dip it off - either one will work - the manual method will probably be quickest with the lowest trauma to the fish. Doubt the small dots you are seeing are the same thing, but if you've got one, you could have two... keep your eye on it.>> Thanks Mike T <<Cheers, J -- >>

Help with Treating Parasitic Isopods, Copepods Bob, <<Not Bob, but JasonC filling in while Bob is away diving.>> I visit your site quite frequently and have found it to be extremely helpful. <<happy to hear it.>> I have a bit of a problem. I have had my tank for about a year now. 55 gallon Marine setup with Emperor BioWheel filter, Protein skimmer, UV, Magnum 350 canister filter. FO tank. It seems I have a parasite problem, but I need some help to identify and eradicate it. My Lunar Wrasse had been acting very strangely for a few weeks. He is losing his appetite more and more these days. There were no visible signs of parasites. All other fish were OK. Within the past week, I noticed a lump developing just above his belly and saw a few spots on his face. Upon closer inspection, the spots appeared to be something "hitching a ride" on his face. They are under 1/8th of an inch in size, translucent white, and oval in shape. They appear to be attached at a single point... otherwise free floating. Tried to figure out what they may be, but can't find anything on the site. <<sounds like isopods - little "pill-bug" type things?>> Even more disturbing is my clown trigger now seems to have a couple of these hitching a ride on his eyeballs. <<that doesn't sound like fun at all.>> All other fish are still OK. Today, I noticed that the wrasse now has a small hole in the lump on his belly, almost as if something was nesting under his flesh and decided it wanted out (Almost seems like the movie alien!) <<that would definitely be no fun>> SG=1.23 Ammonia=0 Nitrites=0 Nitrates=60. I feel as though I keep the water quality at its finest at all times. <<those nitrates could be a great deal lower, say between five and ten.>> The only variable that has changed is that I lost a Kole Tang due to HLLE, so I replaced him with another. I know I SHOULD be using a q-tank for newbies, but I haven't had a problem thus far without one. <<ok, but you are going to get one now, yes?>> Please help. I'm not sure what it is I'm dealing with. <<really does sound like isopods>> I know the worst thing to do would be to panic and throw all sorts of chemicals in the tank (a bitter lesson I learned the hard way when I started the tank!), but I want to keep this problem under control. No inverts, so I could use copper if need be. Any help you could offer would be greatly appreciated! <<Well... most times isopods are best removed with tweezers and are much like pulling ticks off a dog. Your clown trigger though, I don't think I would advise this here as you'd end up with a blind fish. You should probably try an extended [longer than normal], pH adjusted freshwater dip, perhaps even with Methylene-blue to help ease the whole thing. Check the link for Bob's protocols for dipping your fish: http://www.wetwebmedia.com/dips_baths.htm and the isopods... http://www.wetwebmedia.com/parasiti.htm >> Thanks, Jon Beeson <<You are quite welcome. Cheers, J -- >>

Help with Treating Parasitic Isopods, Copepods... (continued) Thanks for the advice.... but now another twist to the plot... This morning, I noticed a brown wormlike parasite protruding from the wrasse's lump. <<Egads>> Should he be removed from the tank? Is this a danger to the other livestock? <<well, you've obviously got these and other things a-plenty so if the fish aren't in danger today, they will be in time. I would definitely take action.>> The wrasse likes to sleep under the substrate... could this have contributed to him getting this worm? <<sounds quite likely but impossible to know for sure.>> Also, how do I treat this worm? Can I pull it out of him with tweezers? <<could, I think I would try the extended, pH-adjusted, freshwater dip and start with that... go after it with the tweezers as a last resort. Many worms can lose an entire chunk of themselves and never miss a beat - grow it all back - kinda like a bad monster movie. If you were to pull at it with tweezers and only get a chunk, likely the rest would survive just fine in your wrasse - nasty. Try the FW dip first.>> Thanks in advance. Jon
<<Cheers, J -- >>

Interesting Find-Cirolanid Isopod Hello Bob et al; I started up a marine tank about 10 days ago. I have been reading and researching on your site for the last few months. My tank has been cycling about 10 days now (ammonia is starting to go down, and nitrites are coming up.) A couple of nights ago, I found what I believed was a Cirolanid isopod, on the substrate, after lights out. I tried to net the sucker, but missed and he went into the live rock somewhere. The next night I put a coke bottle trap in. About an hour after lights out, I looked in the trap, he wasn't in there, BUT he was sitting in the sand outside the trap. Once again I got my net, and with a little skill and a lot of luck, I CAUGHT HIM. I had my wife take pictures of him and I have attached them to this email. Question: Is this the dreaded Cirolanid Isopod? His length was about 3/4 of an inch long. <Not so dreaded... but an isopod. Bob Thanks; Kevin

Re: Interesting Find-Cirolanid Isopod Hello again Bob; Thanks for your quick reply. I have learned a lot from you and your colleagues. But, I thought that the Cirolanid isopods were bad to have in your tank, because they are parasites to fish. I read that they can kill your fish one by one. I thought that they could be identified from harmless isopods by their big eyes, which is why I thought that the one I caught was the bad kind. Maybe I should have left him in the tank. (He's dead now though). Can you clarify? <These crustaceans are rarely of consequence in captive systems, and easily removed as individuals. Bob Fenner> Thanks for providing a great site for all of us interested in the hobby to learn!!! <It is (generally) a great joy, and source of enlightenment to me as well> Kevin D

Cirolanid isopods I hope I'm being helpful... What I've found so far: Fresh water dips may or may not be effective. Reports of these things living for hours in freshwater are not uncommon. Some respond immediately to freshwater dips, others not. <Yes> Putting raw fish into a narrow necked vase can be used to trap them. I'll assume that the cut off coke bottle top inverted into bottom of the bottle would work as well, but see no reports. <Can work... I like a clear tube (plastic, glass) with coarse filter fiber jammed on either side of the meat bait... to entangle the to-be-removed pests (so they don't get out when you're retrieving the trap). The white polyethylene "Grobflocken" by Eheim is best IMO here> There is some talk of juvenile hogfish being effective, but some doubt among others. Some report of Canary blennies, but they seem not to be effective. It seems that the pods will attach to the inside of the blenny's mouth, tongue, or gills and drop off as though it were external upon lights on. The hogfish are reported to be smart enough to chew before swallowing. They reproduce sexually, about 30 at a time. I'm trying the vase method. We'll see. Some have reported trapping over a hundred of them. Reef Central is replete with mail and articles on the critters. <Thank you for this. Bob Fenner>

Creature from movie" Alien" has got my pajama cardinal! Guys, woke up today to find this creature, isopod i guess, clamped on the face, mouth, of my cardinal. Did not look like the poor fish could open his mouth, just like in the Alien movie. Tried to catch fish but impossible in 450 reef tank. Worried these monsters could get out of control, only seen one though. Does any type of fish eat these things? <Not really. Good idea to get/use a fish trap (these are sold in the pet-fish industry (there's an ad in FAMA currently...) or from large warehouse stores (they're the same plastic traps for small rodents, but no fish sticker...> I recently moved a few pieces of rock from refugium to main tank and assume that is how this thing got into main tank. It is quite large, over 1/4 inch. Thanks, Paul <Maybe... bizarre. Catch the host, remove and toss. Bob Fenner>

Cirolanid Isopod Hey bob, I've noticed a wide spread of Cirolanid Isopods in my 18gal live rock tank. I'm guessing the liverock has introduced them into my tank. I read that you recommended a wrasse in trying to exterminate these "bugs". What type would you recommend?  <Mmm, would try baiting, trapping these out in such a small system... likely any Labrid that might do the job would be too big. You can make a tube (plastic pipe, clear or not) lightly stuffed with "filter fiber" with a meaty food in the middle... and "fish" at night> Would a common cleaner wrasse do the job? <No> thanks, Jason <Catch them, remove them, study them. Bob Fenner>

Parasitic Isopods 6/11/03 I recently managed to capture a small .5 inch isopod in my 10 gallon reef aquarium. <yikes!> Amazingly, I had to pull an all nighter to capture this bug in a mantis shrimp trap in which we thought the isopod was a mantis. I have tried the last several nights to find another one using the same method, yet i have not seen one since. <indeed... many are only nocturnal> I am not quite sure if they are all gone, or maybe i have more, so i was wondering if there might be any more methods of capturing another and possibly the babies. Alex <meat in a cage... literally. And a sacrificial fish in a mesh container just the same if you must. These parasites can be scary and hard to remove. They certainly can bite you just the same... look out :p Anthony>

Isopods? 4/6/04  Much appreciated Anthony. I really cannot track anything back to an Atlantic addition to this new tank.  <and they are not restricted to the Atlantic, or even tropical waters for that matter - they are global... like Elvis. They simply are most common in our hobby from Atlantic substrates>  The only things that had been in the tank when they were first noticed are sand (CaribSea) new bags, and Marshall Island Live rock from Premium Aquatics. Tank and all filtration were new. It has to be the LR!  <yes>  I am going to set up a trap method tonight with 1" airline tube, filter floss, and thawed fish. I could seal and send you a specimen?  <I'm really not an expert on microcrustaceans... Ron Shimek really is more experienced/able and interested in such matters. Do consult him at reefcentral.com to send a sample perhaps>  Any thought on taking a good out of water pic? Steve  <above or below the water in a confined area (deli cup perhaps)... I prefer using a flash most always for fast shutter speed. Anthony>

Parasitic Isopods And The Aquarists Who Hate Them! Thank you for your reply, Scott.  I originally believed that velvet killed my new fish and did not look very closely at the dead bodies for other causes.  The velvet was so obviously all over each fish.  Now that I have found the isopods, I also wonder if they played any role in the fish deaths, and that I simply did not think to look for multiple causes at the time. I'm beginning to think these isopods may not parasitic.  From a couple of sources, it is said that isopods which can roll up and swim upside down will be detritivores.  My bugs do both, but I am still very confused. <I have not heard that, but it seems like an interesting theory! I suppose that they could have played some sort of role, but I agree that velvet was probably the primary killer..> As you stated in an earlier reply that feeding the tank meaty foods would definitely prolong the parasitic isopods' lives.  Are you now saying that any decaying food, even plant matter, would give these guys enough to eat until a tasty fish comes their way? <In theory, yes! That's why it is tough to eradicate these little pests.> If so, I'm sorta scr*wed, then, aren't I? <Nope...Just challenged...You will win this battle...> How about if I add household non-scented ammonia to the tank instead of meaty or vegetable foods that will decay? <Personally, if it were me, I'd simply leave things alone, and I'd conduct regular maintenance on the tank. I believe that respiration and metabolic processes of the existing fauna in the tank will provide sufficient ammonia to keep things going> The tank is 72g, with 80+ lbs of LR, lots of soft corals, some unidentified but beautiful macroalgae, 3" aragonite sandbed, and about a mix of 30 Astrea and margarita snails.  Any suggestions to save the tank but kill off the isopods, if they prove to be parasitic, are very, very welcome. Again, thank you for your time and expertise. <Well, it is certainly possible to employ biological controls, such as hogfish, and Meiacanthus species blennies, to mention a few. They are not 100% reliable, but they have been cited by some hobbyists to be predators against these little nasties. In the end, careful observation and patience will be the best counterattack for you. Remember, although they can be dangerous, many fishes can survive the attacks of these creatures until you can treat them. Usually, very small fishes or fry are more likely to suffer fatal occurrences as a result of isopods. Again, I think that diligence and patience on your part will win out. Short of totally breaking down the tank, this is your best strategy! Good luck! Regards, Scott F.>

Parasitic Isopods Hello guys! <Hi there! Scott F. in today> I really need some help. I just set up a new 150 gallon reef and released some fish I've had for some time into it. About a week later (last night) I discovered a small (1/8 to perhaps 1/4 inches) isopod has attached itself to the tail of one of my pajama cardinals. <Yuck> I have not had a chance to even try to capture the fish yet. I know I must capture and remove. I guess what I am asking is I have heard that once you have one (one RC) you likely have a lot more and a typical nightmare. Please tell me this isn't true. It doesn't say that in Bob's book! If it is what should I do? Thank you all so much. Brian <Well, Brian- where there is one, there could be others. Don't run off headless and do something that you'll regret later. Short of "nuking" the tank with aggressive medications (which I DO NOT recommend), you just need to stay very vigilant, and be prepared to remove any fishes that become afflicted with these guys in the future. Remain calm, observe your fish very carefully, and stay alert! Sometimes the best course of action is not to do anything...Regards, Scott F> 

Pesticides for killing isopods... Ahhhh, No. 5/10/04 Hi Guy's <howdy!> Great site! <thanks kindly> Was wondering what your thoughts are on the use of dog heartworm medication (Melbemycine oxime) to eradicate Cirolanid Isopods. <a dreadful idea/advocation... its efficacy runs the gamut, but more importantly, it will kill far many more desirable crustaceans in the main display than bad ones. The bad ones should be/have been easily screened in  a proper 4 week quarantine on arrival> I'm aware I'll loose all crustaceans, at least the ones I don't remove, but see very few options. <Ahhh.. OK. Although I cannot agree> I believe they arrived in the aqua cultured LR that I cycled the tank with. <yes... they are common in Florida live rock... especially that dreadful heavy stuff from shallow coastal waters (many parasites there)> Tank has been up and running for about 6 months. The predatory Isopods made their presence know, at least to me, only this past week. I've caught and removed 3 pods from two different fish. <sigh... I regret you have learned this way as many of us do. But QT is not an option, and must be done for all things wet: fishes, corals, live rock, sand, plants... everything! There are too many pests, predators and diseases that can and will be carried in with live products> A tank raised Perc. And a bi-color angel. The tank is 72g bow front, 85lbs of LR, 4inch sand bed, Thanks for your thoughts on this. Mike <remove the fishes to QT and trap for isopods in the display with meat. Read more on this in the FAQs on this subject in our archives at wetwebmedia.com. Anthony>

External Parasite Good day, <And thou> I recently purchased a Percula Clown fish and he is doing well.  The next morning I observed something attached to his rear tail fin.  It was transparent like having 2 small black eyes and many little legs underneath.  It was almost like a pill bug but more skinny in width and see through (you can see its insides).  It even had a tail of some sort and closely resembles a small crustacean or something. What is this? <Likely as you describe, infer... a parasitic isopod> I immediately removed the clown fish and placed him in a freshwater dip for about 3 minutes.  This thing obviously didn't like the fresh water and soon fell off swimming in circles on the bottom and eventually dying. <Good move!> Did this thing come from the live rock in the tank (I have 27 pounds in a 55 gallon setup).  It obviously came from somewhere because it was not attached to the clown when I purchased him at the store.  I searched long and hard to find a photo of this thing and I can't find out what it was.  So far this is an isolated incident.  Should I be on the lookout for more or should some sort of treatment be started.  Or, did I do the right thing and I can sit back and relax because this won't hurt the fish.  If this happens again do I proceed the same way? <Yes, yes, yes> Thanks for taking the time to help, Dave <Take a read here Dave: http://wetwebmedia.com/isopoda.htm and the Related FAQs (linked, in blue, at top)... such incidents are rare, but do happen in aquariums. Bob Fenner>

External Parasite Good day,<Hello, MikeB here.> I recently purchased a Percula Clown fish and he is doing well.  The next morning I observed something attached to his rear tail fin.  It was transparent like having 2 small black eyes and many little legs underneath.  It was almost like a pill bug but more skinny in width and see through (you can see its insides).  It even had a tail of some sort and closely resembles a small crustacean or something. What is this? I immediately removed the clown fish and placed him in a freshwater dip for about 3 minutes.  This thing obviously didn't like the fresh water and soon fell off swimming in circles on the bottom and eventually dying. Did this thing come from the live rock in the tank (I have 27 pounds in a 55 gallon setup).  It obviously came from somewhere because it was not attached to the clown when I purchased him at the store.  I searched long and hard to find a photo of this thing and I can't find out what it was.  So far this is an isolated incident.  Should I be on the lookout for more or should some sort of treatment be started.  Or, did I do the right thing and I can sit back and relax because this won't hurt the fish.  If this happens again do I proceed the same way? Thanks for taking the time to help, Dave <Dave, try looking up Planarian on the internet.  My hunch is that it is a flatworm parasite.  It can be prevalent in fish that are purchase and not quarantined for an extended amount of time.  I would suggest keeping a close eye on the fish an make sure it doesn't come back.  If it does then quarantine it.  Thanks MikeB.> <<Likely is a pill bug... a parasitic Isopod. RMF>>

Isopod with a taste for Beef Steak Dear Bob, <Bob is out right now. Mike G here> I just woke up this morning to find that my young tomato clown, Beefsteak, had some sort of external parasite attached to his posterior dorsal fin.  <Never a good sign.> The organism appears fairly complex and I can observe a segmented body along with two spots which seem to be eyes. I would estimate it's size to be somewhere around 2-4mm in length and of a light grey color, darker grey near the head. <Sounds to me like a Cirolanid Isopod> My best guess would be that this is some form of an isopod although I've never seen one attached to a fin in this way and it is rather small. <Everything starts small and grows when provided with nourishment. In this case, your fish is providing the nourishment.> I don't know if I'd be able to get the little clown out of my 55 gallon reef without destroying anything in the process. Do you think I should worry about this little parasite, because I most definitely am. <ANYTHING attached to and feeding on your fish should concern you.> I mainly do not want him spreading to any of my other fish. Any information you can give me would be much appreciated. <Here are a few articles and FAQs on Cirolanid Isopods. http://reefkeeping.com/issues/2002-05/rs/index.htm  http://www.wetwebmedia.com/isopoda.htm  http://www.wetwebmedia.com/isopodfaqs.htm  I wish you the best of luck in exterminating this parasite. Mike G>