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FAQs on the Gambusia, Heterandria spp. Mosquitofishes

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Hi Neale - Heterandria formosa, hlth..      8/10/13
Hi Neale,
How are you?
<Well, thank you.>
One of my Heterandria formosa has... whitening at the end of her tail and it looks like the top part of her caudal fin is gone.  The white spot is a large area of lack of color starting on the base of the body (I believe it is called the caudal peduncle or keel) and extends into the caudal fin. 
It does not look like icky. 
<It's not... it looks like fungus.>
Pictures are attached.  I have noticed a second smaller fish that looks like it is developing the same white spot.  I'm wondering if the tank should be treated with medicine, and if so with which?
<A reliable anti-fungus medication; at this point I'd skip Melafix and find something a bit stronger and more reliable. I'd also be tempted to add salt to the water if the rest of the tank won't mind. 2-3 gram/litre would be a good start, and above 5 g/l (about a tablespoon per US gal.) the salt alone will usually clear up the fungus. Do bear in mind Heterandria formosa has very good tolerance of salt, so there's little risk involved using salt.>
Water Parameters (this right before their weekly water change):
pH 8.0
Ammonia 0 ppm
Nitrite 0 ppm
Nitrate 20 ppm
Kh 7 dkH (125.3 ppm/KH)
GH 17 dKH (conversion chart doesn't go that high, but 17 drops to go from orange to green)
Temperature is in the mid 70Fs, there is no heater in the tank.
This is the same tank and colony we chatted about a few years back (and I still have the Gambusia affinis in another tank).  No new plants, fish or shrimp have been added to the tank since 2010.  (I tried Cherry shrimp but none survived, probably from the Prazi Pro in the tank a few months before for deworming).
I'm also wondering if I should deworm the colony again, I have noticed a few females that get really thin.
Thanks for your insights and advice!
<Hope this helps, Neale.>

Re: Hi Neale - Heterandria formosa    8/12/13
Hi Neale,
Thanks for your reply, I'll get some anti-fungus medication today.
<Real good.>
There is java moss in the aquarium, will it be okay with a tablespoon of salt per gallon?
<Yes, but if in doubt, take a clump of moss out, stick in a jam jar or similar, fill with water, and place somewhere bright but not in direct sunlight, and it should grow fine for a couple weeks, enough to "re-seed" the tank if needed. You will probably need to change the water every few days, especially if it goes green. If it goes brown, likely the Java Moss is getting too hot, hence avoid direct light. This trick for preserving aquarium plants can be handy if you have plants that you aren't sure will
survive some course of medication.>
If so, is marine salt (like Instant Ocean) okay to use?
<It's okay, though it will raise hardness and pH (which is fine for both Java Moss and Dwarf Mosquitofish). Normally aquarists treating freshwater fish will rely on plain aquarium salt (essentially non-iodised cooking "sea salt", often called Kosher Salt in the US). But in this case, the marine aquarium salt will be fine because your species don't mind the slight pH
and hardness rise.>
<Quick tip: measure out the salt as required, put into a jug or container, add warm water to dissolve (tap water will be fine) to make a brine. Now add, in stages across, say, half an hour, the salt to the aquarium. This gives the fish, plants and filter bacteria a little time to adjust. Adding salt crystals directly to the aquarium is a bad idea, but I'm sure you know that! Good luck, Neale.>
Re: Hi Neale - Heterandria formosa     8/13/13

Hi Neale,
Thanks for your help.  I bought Ampicillin and started treating yesterday.
Will the fish that in the photographs be okay to leave in the tank, or will leaving her in increase the chance of fungus returning?
<The fungi that attack your fish are the same fungi that do a good job helping to keep your aquarium clean. They're purely opportunistic, and if your fish are healthy and unstressed, they simply break down fish faeces and uneaten food into molecules the biological filter can process -- which is obviously important and beneficial. So, there's no point isolating fish
with fungal infections because all aquaria have these fungi anyway. In other words, treat the affected fish in the main aquarium. The exception would be where the infected fish had other problems that meant it couldn't swim or feed normally, and needed time away from the other fish in the main aquarium. Cheers, Neale.>

Re: Hi Neale - Heterandria formosa     8/14/15
Thanks Neale!
<Welcome, Neale.>

Guppies and mosquito fish, incomp.  1/17/12
I have been raising guppies for awhile now, but I am new to the mosquito fish. I have one or two female and two or three males mixed in with my guppies. I have noticed that the mosquito fish are very aggressive.
<Yes. Don't mix them with Guppies because of this.>
My question is can they interbreed with my guppies?
<They'll certainly mate, but I'm not aware of viable offspring being the result.>
I have some new males that just appeared in my tank which have not grown very big compared to my other guppy males and have very little color. I recently added a multicolor male guppy the other day and within a day before my eyes this little red guppy I believe to be a mix between the guppy and mosquito tore up his really pretty tail of my new guppy in a matter of minutes. Well at least I believe them to be mosquito fish, they look like guppies but they came from the local river.
<Cheers, Neale.>

Jumpers?    10/26/11
I just bought some fish I have not kept before, Dario dario and Heterandria formosa. I intend to keep them in (separate) planted species tanks. I'm just wondering whether I need to worry about either species jumping.
<Both can/will leave; the Dario more than the livebearer. Bob Fenner>

Hi Neale - Heterandria formosa [RMF, second opinion please]<<>>  7/31/10
Hi Neale,
How are you?
<Just fine and dandy, thanks!>
I have some wild caught Heterandria formosa in my quarantine tank.
<Lucky you! What fun these will be.>
I've had them for about six weeks and I think they might have parasites.
<Is always possible with wild-caught fish, and deworming would be a good idea.>
The new Hets look thinner than my main colony I have which I don't think is very surprising since they have recently come from the Florida wild and have traveled across country and have to get used to captivity.
Every now and then a female starts looking like she is wasting away and then a few days later dies. This has happened to three females. Also, almost twenty Hets arrived, and I have not noticed any babies yet.
The water parameters are 0 ammonia, 0 nitrite, 0 nitrate. 10 gallon tank with java moss, no substrate, small Aquaclear filter, room temperature about 75F. The tank was completely cycled and has been set up since November. I've had other fish go thru quarantine in this tank with no problem and cleaned the tank, but kept the same filter before the Hets arrived.
<All sounds fine.>
The only fish in the tank are the ones that came in the shipment. I noticed there is a whitish male livebearer that can't be a Heterandria formosa but I am not sure what he is. I was going to move him into another tank away from the Hets but haven't because of the female deaths.
<Gambusia affinis is often found alongside Heterandria, so I wonder if the white fish is one of these?><<Me too>>
They are being fed frozen baby brine shrimp, frozen rotifers, and a mixture of Ocean Nutrition Prime Reef flake and Spirulina flake and occasionally some freeze dried daphnia.
<All sounds perfect.>
In my main Heterandria formosa tank from time to time (before the new wilds arrived) I have noticed a female that is very thin and doesn't look pregnant, and I wondered if they were towards the end of their natural life
cycle. The main tank is producing fry like crazy.
<Oh, certainly, these fish are largely annuals in the wild. My instinct would be to lower the water temperature a bit, to maybe 72 F/22 C, add a tiny bit of salt, maybe half a teaspoon per gallon, and deworm them. The lower temperature is to slow everything down a bit, and a reflection of the subtropical nature of these fish -- here in England they're usually sold as coldwater fish. The salt provides a little therapeutic support for livebearers and can be useful when they're not doing well, even though you're right to assume these are freshwater rather than brackish water fish. Deworming should help shift any internal parasites.>
There has been no water transferred from the quarantine tank into the main colony.
Do you think there is any medicine I should treat the quarantine tank with?
<Yes, as stated above, I think worms are the most likely problem here, if only because external parasites would be obvious.>
As always thanks for your help!
<Cheers, Neale.><<I too suspect these are "last years" breeders. RMF>>
Re: Hi Neale - Heterandria formosa [RMF, second opinion please]  7/31/10
Hi Neale,
Thanks for quick reply.
<My pleasure.>
I just looked up Gambusia affinis, and I think that is what he is.
<Oh dear.>
He does try to mate with the female Hets.
Long term, can he live with the Hets or should he be moved into a non-Het tank?
<Needs moving. Gambusia are nippy and very aggressive, and he will eventually kill off the male Heterandria, given the chance.>
How do I deworm them? Is there a dewormer I can get at my local pet store?
<Oh, yes, should be something available. Prazi Pro, etc.>
While I am at it, should I also deworm the main colony?
<I would.>
I have Instant Ocean salt, would that work or should I get some aquarium salt?
<This is fine, perfect even; will harden the water and raise the pH a bit, both positives.>
Can I add 5 teaspoons to my next batch of water getting ready for a water change (they are in a 10 gallon) so they will get all the salt added at once?
<By all means do this. Heterandria formosa is found in brackish water, and I suppose if these were collected in such, they might not be handling straight freshwater so well.>
I think my apartment might be on the warm side for them. I've read their native range is up to 81F,
<In summer, yes, but down into the mid 60s much of the rest of the time, and potentially lower still in winter. Upper 60s, lower 70s is generally considered optimal. But of course, the warmer they are, they shorter they live.>
so I was hoping mid seventies would be fine.
<Should be, but perhaps add an airstone during the summer months. Maybe float an ice cube and see if the fish cavort in the cool water -- if they do, it's a good sign they're feeling a little warm.>
I'd have to crank the AC in my apartment to cool them down (e-x-p-e-n-s-i-v-e-!). Would a chiller be a sane, safe, stable thing to add to a 10 gallon aquarium (the main colony) or would that be silly/extreme?
<Cheers, Neale.>
Re: Hi Neale - Heterandria formosa [RMF, second opinion please] - 8/1/10

Hi Neale,
"Needs moving. Gambusia are nippy and very aggressive, and he will eventually kill off the male Heterandria, given the chance."
Oh dear. Would he behave himself with Cardinal Tetras or harass them?
<Harass them. Gambusia affinis are wonderful lab animals but bad aquarium fish, and a real pest in the wild where they've been thoughtlessly introduced.><<And Cardinals live in much warmer, softer water>>
I've called around to the pet stores, would Metronidazole work? I also could drive across town and get Prazi Pro, is either better in this situation?
<The latter would be my preference. Metronidazole isn't a dewormer.>
I've never tried the floating the ice cubes in a baggie trick. I know someone who is adamantly against this, the difference in temperature is too extreme for the fish to be exposed to he claims.
<Your friend is worrying too much. A few ice cubes will create cold water that sinks, and the fish will either swim into that cool water or avoid it, as they prefer. The overall cooling effect on the whole tank will be very small, less than one degree if the amount of ice is one-hundredth or less the volume of the tank. Basically, try it yourself and see what happens.>
If it is safe, I'll try it.
<It is safe, and floating sealed cartons of ice about a litre in size in aquaria is standard operating procedure for gently cooling over-hot tanks.>
Thanks again for your help!
<Glad to help. Cheers, Neale.>
Re: Hi Neale - Heterandria formosa [RMF, second opinion please] - 8/1/10
Hi Neale,
I just gave fifty percent water changes to the main Het colony and the quarantine tank and gave them both a treatment of Prazi Pro. The salt was added to the quarantine tank during their water change.
Should they be retreated again, or is one dose sufficient? Should they be treated in the future on a regular bases for prevention?
<Use as per the instructions for this particular infection. Once the course is finished, you shouldn't need to treat again.>
Also, I know worms are common with livebearers but should I use Prazi Pro on the Cardinal Tetras, and another tank with Redigobius balteatus and shrimp? I try to not transfer water but it is likely the tetras and gobies
got a little water from the main Het colony.
<It's unlikely the other fish are infected, and I wouldn't treat the other fish unless there was good reason to do so. Check toxicity re: snails and shrimps; some antihelminthic medications are toxic to these.>
Living arrangements. The main Het colony has fifty fish give or take a dozen in a ten gallon. The quarantine tank has almost twenty, which I bought to give the main colony more genetic diversity.
How many Hets can a ten gallon have before it is over crowded? There is a huge ball of java moss and
water conditions are 0 ammonia, 0 nitrite, 0 nitrate.
<I'd have though you could have 20 in a tank this size without problems.>
I don't have room for a permanent tank to split the colony, but I have been thinking about moving some in with the Redigobius balteatus and letting the fry be a food source. I could also swap out the tank and fit a fifteen or
twenty high on the stand.
<Should work fine. Heterandria tolerates brackish water well, and both will thrive at SG 1.003 or thereabouts, which makes planting the tank easy.>
If some Hets don't move in with the gobies, could the Gambusia move in with the gobies?
<Wouldn't bank on it. Worth a shot, as sometimes gobies stay out of trouble with nippy fish for reasons not clear to me. But Gambusia just isn't a good aquarium fish.>
If he can't I'll see if a local fish store that sells "mosquito" fish will take him.
<Or keep with something a bit larger and just as feisty, such as Ameca splendens or maybe a Figure-8 puffer.>
Hate to sound like a broken record, but thanks again for your help!
<Cheers, Neale.>
Re: Hi Neale - Heterandria formosa [RMF, second opinion please]  8/1/10

Hi Neale,
Thanks again for all your help, really appreciate it.
<Happy to help.>
I'm out of housing options for the Gambusia. I'd like to keep him but there is no place to set up another tank, I've been trying to figure out how to get another one in here for quite awhile. That is too bad, he is a very nice looking fish.
<Indeed. I have seen them kept in rough communities with things like armoured catfish and medium-sized cichlids, but not altogether successfully. They do make good pond fish if you're somewhere with the right climate. I dare say they'd mix well with small turtles too, and likely amphibious crabs. But generally, no, they're aren't good community tanks.>
Thanks again,
<Cheers, Neale.>

Re: Hi Neale - Heterandria formosa - Cherry Shrimp & PraziPro   10/13/10
Hi Neale,
How are you? I hope all is going well!
<I'm fine, thanks for asking.>
The PraziPro worked, the Heterandria formosa are doing great; thanks for the advice.
I gave my 10 gallon main Het tank a single dose at the beginning of August.
Would it be safe to add Cherry Shrimp (Neocaridina heteropoda) to the tank? It is bare bottom, has a sponge filter and a lot of java moss.<Should be fine by now. Try half a dozen and see what happens.>
I can't find copper listed on the bottle but I've heard other medicines can affect shrimp and I want to make sure the PraziPro won't effect them.
<Prazi Pro contains Praziquantel, and yes, it probably is toxic to shrimp.
But assuming you've done a series of water changes, the amount left in the aquarium should be trivially small, partly because of dilution but also because filter bacteria break down organic compounds fairly quickly.>
<Sounds like you're having fun with these very nifty livebearers. Cherry Shrimp appreciate much the same conditions, so this combo should work nicely. Cheers, Neale.>
Re: Hi Neale - Heterandria formosa - Cherry Shrimp & PraziPro   10/14/10

Hi Neale,
I've been thinking about Cherry Shrimp for awhile and some have are available now.
I'll give my tank a couple extra water changes to be safe and get some next week.
Can the shrimp go straight into the main tank, or should they be quarantined?
<<Depends. The free-swimming Whitespot pathogens can move from tank to tank on any wet object, be it alive or dead, so yes, Shrimps can carry them. But the pathogens can't survive away from fish for more than a day or two, a week at the outside. So if the shrimps have been kept in a fish-free aquarium isolated from aquaria containing fish, including different nets and buckets, there is little risk of the shrimps carrying any diseases at all. On the other hand, if you can't be sure they've been isolated, then yes, quarantining is a very good idea. I will make the observation that both shrimps and Heterandria have a high tolerance for salt, so using the salt/heat method to treat for Whitespot will effectively "clean" the shrimps if you add them to the aquarium directly, and without any risk to either fish or shrimp.>>
Also, I bought some Indian Almond Leaves off eBay; would the shrimp like those in the tank?
<<Sure, but why bother?>>
<Sounds like you're having fun with these very nifty livebearers. Cherry Shrimp appreciate much the same conditions, so this combo should work nicely. Cheers, Neale.>
The Hets are really a lot of fun! I started with a handful and it is neat to see new babies all the time and watching them dart through the Java Moss.
<<Definitely nice fish.>>
I think it is great that a lot of different types of aquariums are doable in people's homes. As a matter of fact, even though I have three tanks, I find myself thinking about other aquariums I would like, and I think some articles about Multi Tank Syndrome on WWM would be a good idea. :)
<<Ah yes, there's always another fish worth keeping! I agree, reading some articles about how to make fish rooms and aquarium racks would be a nice idea. I've seen several people convert their basements into fish rooms, and there's a lot of work involved doing the air pumps, wiring, plumbing and so on. Naturally, if *you* feel like writing something about the care and maintenance of your livebearers, why not check out back page of WWM Digital magazine and read up on what we offer authors!>>
Cheers, Michelle
<<Have fun! Cheers, Neale.>>

Gambusia question   7/17/10
I recently purchased 12 Gambusia fish from Carolina Biological Supply to place in my outdoor fountain for mosquito control. My daughter had other ideas and insisted that we keep some in an aquarium. This has worked out well as we occasionally lose a fish in the fountain and the tank fish provide a nice source of replacements. I would however like to add some visual interest to the tank as it is viewable from my living room but am unsure as to what additional and inexpensive fish I can safely add to the tank. Your suggestions are appreciated.
<Hello Amanda. Unfortunately, you really can't add anything to tanks with Gambusia. They're pronounced fin-biters, so anything kept with them tends to get attacked, even catfish. Inevitably, they end up being kept alone.
That's why they are almost never sold in the aquarium fish trade and only marketed via biological suppliers as lab animals or whatever. About the only thing I can think of that might work is Ameca splendens, since this Goodeid has the same requirements for subtropical temperatures, hard water, and algae-based food. It's a bit bigger than Gambusia affinis, a strong swimmer, and a bit nippy in its own right. But even then, I'd have a Plan B handy in case this didn't work. For what it's worth, Ameca splendens is much prettier than Gambusia affinis, and as a subtropical pond fish would perhaps be a better choice. Cheers, Neale.>

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