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Internal parasites??

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     Hi Everyone,

    I bought several celestial pearl danios (Celestichthys margaritatus) and dwarf emerald rasboras(Celestichthys erythromicron)from local fish stores 4 months ago. I picked seemingly healthy specimens, I notice that all of the fish would do well in my tank in the first couple of weeks but some would gradually become emaciated, and finally died. It seems to be contagious but the “infection” process could be very slow, I lose 1-2 specimens every month. And this Phenomenon only occurs in C. margaritatus and C. erythromicron , other species in my tank are not effected. 

    the sick fish would be still eating at first, but no matter what and how much I feed them, they become skinny, have sunken belly and then refused to eat/spit out any food. 

    I have had several hypotheses:

    1. Internal parasites. I tried Metronidazole Tablets, 200mg for every 10 gallon, used over 2 weeks, in vain.

    2. Bacteria infection. I tried  Maracyn 2, which contains minocycline. (http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=4842), dose is according to the instruction, used over 2 weeks, in vain.

    3. Now I doubt if it’s because pressure resulting from too many fish in the tank. Or, C. margaritatus and C. erythromicron could be genetically vulnerable to such disease?

    I tested water parameter at local fish store, forgot the number but Ammnonia, Nitrite, Nitrate are all good. Haven’t tested GH/TDS yet, will do if needed. 

    I feed them crushed flake food, crushed dried blood worm, frozen daphnia, forzen baby brine shrimp.

    I searched the internet and found at least for C. margaritatus, refusing eating/sunken belly can be quiet common and hard to reverse.

    pH: 7.7
    Temperature: 24-26.5 degree Celsius

    Tap Water Parameters: Ph 7.7-8.0
    Test kit used:
    (Liquid or strip)

    Tank Size: 20 gallon(60cm*30cm*40cm)
    (Dimensions & Volume

    Length of time set-up: 7 months
    Filtration used:(Type & media)

    1 Hang on back filter(71 gallon per hour); media: sponge, activated carbon.

    1 canister filter(106 galloen per hour); media: sponge, activated carbon.

    Maintenance Schedule: weekly change 1/5 water and wash sponge. I use tap water but will expose water under the sun light for 3-4 days before using.
    (Amount of water changes? How often?
    dechlorinator used? Filters cleaned? etc.)
    Detailed stock list:
    (Species, size & how many)

    animals: checkered barb(Oliotius oligolepis) 2 male, 2 female. size: 3-4 cm each

                 kuhli loach *3. size: 5 cm each

                 C. margaritatus *10, approximately 5 male, 5 female. size: 2 cm each

                 C. erythromicron *10, approximately 5 male, 5 female. size: 2 cm each 

                 Dario dario  2 male. size: 2 cm each 

                dwarf chain loach (Ambastaia sidthimunki ) *3. size: 4 cm each

                amano shrimp *2

                cherry shrimp * 10+

    plants: Anubias sp.Cryptocoryne sp.; Vallisneria sp.; Java fern, Java moss, few duck weed

    decoration: rocks, pebbles, gravel, drift woods. 

    The tank is forest stream type, will upload pictures if needed

    Recent additions to tank: C. margaritatus & C. erythromicron , cherry shrimp *2
    (Fauna & flora)
    What fish are affected: C. margaritatus & C. erythromicron
    What are the symptoms: see above

    Treatment already used: see above



    This sounds like to could be a microsporidia (Pseudoloma neurophilia) infection. This is a chronic problem in zebrafish labs and has been the subject of a fair amount of research (see link below). It has also been found in zebrafish from a lot (but not all) of fish farms that supply fish stores. It is not clear how widely among fish species this parasite be infective, but it can infect several danio species.

    It is slow acting and takes a while to spread

    Alternatively, it might be Neon Tetra disease (Pleistophora hyphessobryconis), which is also a microsporidian.It has been found in zebrafish and a several other species (tetras, zebrafish, barbs, goldfish).

    These are weird parasites that mostly lives inside of cells of the animals it is infecting. It is only found as a highly resistant spore outside of cells.

    There is not yet an effective treatment for infected zebrafish.

    Here is a link to description and details.



    Consistent with mycobacteria too.



    True. Its not uncommon for Mycobacteria to show large red lesions on the skin and sometimes diffuse red areas like around the nose (in zebrafish anyway).



    It is very common in rainbows and *usually* is indeed linked to lesions or ulcers. But usually does not mean always, and in other types of fish it often has no lesions but rather loss of weight and spinal deformities as symptoms… or in a smaller fish like the poster has it may be symptomless.

    additionally, loaches, corydoras and plecos are usually immune … dario I’m not sure about.

    barbs should not be immune so I’d expect them to croak too (but this would likely be the case with microsporidia as well).

    BTW, there is yet another possibility here: these barbs are allegedly peaceful…. but I would not totally exclude them harassing small danios to death.



    Thank you guys! You are really professional!

    Next question is what to do now? Shall I take out everything and wash the tank? For the remaining “healthy” danios, shall I quarantine them? 



    Mike is right. Both of these diseases can be carried by a fish without symptoms.

    Mycobacteria is NOT a obligate pathogen. It can survive without a host in an aquarium.

    Microsporidia can exist as spores out side of a host (but for how long I don’t know.

    I don’t believe either can be really treated well.

    Both may be (but not always) without symptoms until they are stressed in some way.


    I would remove affected fish. Probably all the fish of the affected species.

    Remove any dead fish immediately. Eating dead fish is thought to be an important (but not the only) way Microsporidia is transmitted.

    If I were concerned about the other fish getting infected, I would put them in a new clean tank and strongly bleach everything in the infected tank. More bleach and longer soak times make for a stronger bleaching. I use a lot of bleach (10% of residential bleach, which is usually about 5-6% bleach) for hours or days if I want to nuke something.

    Things like nets that can not be bleached (because they will fall apart) might be treatable by other methods (like iodine or maybe a good net dip if it exists). Alternatively you could autoclave (high heat and pressure) them. Not everyone has an autoclave, but a pressure cooker does the same thing. Some nets have parts that will melt. Try one wrapped in foil to contain the possible melted plastic. Dry materials at the top pressure cooker temperature and pressure for 15-20 minutes will probably kill everything.

    Using a UV “sterilizer” (irradiation level as described in the article above) can help because it can kill circulating spores and bacteria. I use UVs on recirculation systems of several tanks but not single tanks or tanks on flow though water systems. Keep UV bulbs up to date. Their output goes down over time and they should be replaced every 6 or 12 months depending on how how much dose you want and how fast their output goes down. The bulb manufacturer should be able to provide info (probably on their website) on the rate of decline of the bulb’s output.

    Both of these pathogens have been removed (with great effort) from very large operating research facilities, but it takes a few generations (fish generations) and molecular screening to identify carriers to do it. Most places don’t. They do things like trying to clean up their tanks and water systems, clean all the eggs laid in the facility with something like bleach (problem is bleach will kill the eggs at high enough levels to kill all the pathogens). Alternatives to beach being tested include iodine and hydrogen peroxide. Controlling the pH during these treatments can also affect the outcomes, but I don’t remember the details. These would all require testing before using. Bleach for example comes in different concentrations and different purities. Cheap bleach, presumably with impurities is much more lethal to fish eggs than more pure research bleach. For egg bleaching, I use bleach from Sigma chemical supply company (which is up around 10%).



    Thank you guys! You are really professional!
    Next question is what to do now? Shall I take out everything and wash the tank? For the remaining “healthy” danios, shall I quarantine them?

    I’d follow what Bill suggested and simply watch and remove the dead fish for a couple of months.

    I’d not go into nuking the tank at this point.

    The reason is that we did not diagnose the problem. Both possibilities we mentioned are only guesses. It may be something else altogether, like chemical poisoning … I had a case of losing fish slowly due to a piece of ceramics … took a long time to figure this out … cases of bad tap water are not uncommon too. And there are other possibilities.

    Now, if it is mycobacteria or microsporidia .. the former is difficult to treat, I’m not sufficiently familiar with the latter to know if it is possible to fight it or not (Bill? — any comments from you on this?). BUT: both diseases are specific to some types of fish. Loaches for example are immune to myco … dario may be too… shrimps of course are too… so you can run the tank, just do not add cyprinids or any myco-sensitive fish to it and the fish you have now will live normal lifespan.
    microsporidia — well, you need to know exact species of the pathogen for an informed decision — but overall the chances are that it will not affect anything but cyprinids.

    (I hate suggesting things like this… but if you were to try small rainbows in this tank … if you see them going the way of danios, this is probably mycobacteria, if you see them doing fine, this is NOT myco for sure.)

    As for the danios you have left: they are probably doomed either way… you can try curing them from mycobacteria … but do this in another tank. I can give you a link to treatment discussion and a successful case.)




    One more thing:

    Tap Water Parameters: Ph 7.7-8.0

    go and measure TDS before doing anything. With your pH, it may be high enough to kill these danios, no disease needed.



    Much appreciated! Began to worry about my barbs, they look fine though…will watch and take out emaciated specimens, hope some of them will survive



    Hi everyone, 

    I have some updates about the tank. 

    1. I measured TDS in my tank, it’s at least 180ppm, the tap water TDS is at least 180 too. Nitrite: 0
    Nitrate: 0. KH: 120ppm.

    2. The barbs, darios, and loaches are still doing great so far.

    3. I took out all the danios and washed the everything with hot water, I didn’t bleach everything coz it’s too time-consuming. After 2 weeks, I put some white cloud minnow into the tank. I thought since white cloud does not belong to danio they would be fine. they were fine until several days ago, one of the minnows suddenly stopped eating.


    any ideas?

    Now I’m thinking abandoning all the minnow-shapped fish. Cry



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