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FAQs on the Livebearing Toothed Carps, Poeciliid Fishes Behavior

Related Articles: Poeciliids: Guppies, Platies, Swordtails, Mollies by Neale Monks, Livebearing Fishes by Bob Fenner,

Related FAQs: Poeciliids 1, Poeciliids 2, Guppies, Platies, Swordtails, MolliesLivebearer Identification, Livebearer Compatibility, Livebearer Selection, Livebearer Systems, Livebearer Feeding, Livebearer Disease, Livebearer Reproduction,


Guppy age at 1/2 inch; repro.      1/6/18
I have scoured the web simply trying to find out if guppies at the size of 1/2 inch are capable of breeding, or at what size they will become viable for breeding. It seems like a simple question and yet I can not find any age to size ratio chart to know how old they are at 1/2 inch.
<Half an inch is a bit small; three-quarters of an inch (overall... not fisheries/standard length) is more about right; though the fish might be stunted and capable of giving birth. Bob Fenner>

How do fish determine each other's species and gender? Poeciliids   1/8/12
Obviously, not all fish will mate with each other, but how do fish determine each other's species and gender? 
Watching my male guppies perk up & strut their stuff when a female guppy swims by never ceases to amuse and considering their degree of practically relentless enthusiasm for females of their own species, I couldn't help but wonder why the female swordtails in the same tank fail to elicit a similar response.
<The simple answer is evolution: those males that mated with the wrong species failed to father any offspring, so they died out. It's a bit more complex than this, and often both sexes will do things to ensure they mate with members of the right species, but even so, hybridisation is common among fish. But on the whole, animals will have a variety of ways of ensuring they only mate with members of their own kind, and thereby ensure the energy they put into mating is rewarded with viable, healthy offspring. Cheers, Neale.>

Livebearer behavior    9/23/11
I was wondering why Platies and mollies come up to you when you approach the tank, as if they are being social. I think guppies do this to, but I noticed that swordtails will not do this. When I put food in the tank, the Platies come over, but the swordtails just zip around. Do you know why they do this?? Thank you!!
<The farmed livebearers you can buy in most aquarium shops have been bred in captivity for dozens of generations. They associate humans with food, and come to the front of the tank in anticipation of a meal. Many animals will learn this behaviour. Swordtails are fish from streams and are meant to zip about, and they may or may not come to the front for food depending on what's on their mind at the time. Being "social" probably has little to do with this; Guppies and Platies surely aren't "intelligent" in any meaningful sense, and would probably come to the front of the tank whoever it was standing there. Nonetheless, you can at least reflect on their ability to associate humans with food, no mean feat in itself, given the tiny brains these fish possess. Cheers, Neale.>

flashing   6/21/11
I just caught one of my male Endler's flashing. Any reason not to use the PraziPro I have on the shelf left over from the Camallanus episode?
<Don't medicate unless there's a reason to treat for a particular disease with a particular medication. Flashing is more often caused by non-zero ammonia and nitrite, Whitespot, and especially velvet. But it's normal for fish to flash occasionally, just as a dog scratching doesn't necessarily have fleas.
Cheers, Neale.>

Platy, Poeciliid beh.   6/16/09
Dear Crew,
<Iguana del sol>
I ten gallon tank with two Mickey mouse platys(male and female), two guppies(male and female),
and on female red wag platy. When I first put them in together they were all fine, but all of a sudden my red wag platy has wanted to stay alone.
I'm not sure if there is anything wrong, I am just concerned.
Thank You
<Mmm, good observation, but not likely anything "wrong" here... Some livebearers do "take a break" from social interaction at times. If your other fish's are fine, water quality checks out, I would not be overly-concerned. Bob Fenner>

Re: Platy, Poeciliid beh.  6/18/2009
Dear Mr. Fenner,
Thank you for your answer. The day after that happened, I did see that she was with the other fish and seemed fine. Sometimes I am a little too protective with my fish as you can see.
Sorry for the trouble!
<No worries. Bob>

Re: fish foraging and pooping too much? pls help   3/15/09
Hi Neale,
O.k. thanks for the info! I did not realize these species are more herbivore than anything else. I had read this about mollies but not so about platies and swords.
<They're all pretty similar in habits. Mollies and Platies are more herbivorous than Guppies and Swordtails, but it's a difference of degree rather than a binary herbivore/carnivore thing.>
Even books written about "livebearer care" don't really state that they are herbivores in the wild etc. so it all makes sense to me;
<Odd. If all else fails, Fishbase is a useful resource. It reports on what fish eat *in the wild* which is often very different to the information fishkeepers (and fish book writers!) shuffle amongst themselves. Fish will happily eat meaty foods all day long, just like humans will eat steak over salad. But as any nutritionist will tell you, it's the fruit and vegetables humans need to stay healthy, not the steak. Likewise for fish; once you understand what it is they need, keeping them in good health is easier.>
will also get a thermometer to check on the temperatures. We do not use a heater as we live in a tropical country (Singapore) and a lot of people don't use heaters here for most fish but I should take a reading of or daily average. We don't really get significant fluctuations here.
<Singapore should be about perfect for Swordtails and Platies, both of which come from the cooler end of the temperature range and actually enjoy cool nights/warmer days. Fluctuations between, say, 18 C at night and 25 C during the day would suit them perfectly. In fact warmer conditions don't agree with them at all, and can shorten their lives.>
Thanks again and all the best,
<Cheers, Neale.>

Guppies - male swimming funny 03/03/09 Good morning, I have a 10-gallon tank, and I'm a very conscientious new aquarist (about 6 months) with some success. We have some Corys, male guppies and Lampeye tetras in our tank. I've been testing the water, cleaning the tank & filter, feeding not too much/too little, feeding high-quality pellets and changing 30% of the water every week since we started our tank. All except for this past month. I went on vacation and bought an automatic feeder. I set it for once in the morning and once at night, and I used cheaper flakes because the pellets seemed to fall out too fast. I went a bit over 2 weeks before changing the water prior to vacation, changed it right before I left, and then the poor guys went another 2 weeks while we were gone. When we came back, they still had lots of food floating in the tank, so I immediately changed the water. We lost one guppy, and now another is swimming head up/tail down, a bit jittery, and a majority of the time in one place. He's still eating, and he does swim around sometimes. But, he's not swimming like his normal self, though I will mention he doesn't look as bad as the first one we lost. Since then (about a week ago), I've cleaned the filter, changed the water (30%) every day, and tested it: Nitrates: 0-5 PH 7.0 These numbers seem fine, are they not? I don't have an ammonium tester - could that be the problem? Could the cheap food flakes have caused this? How often do you think i should change the water now? It did seem to help when I changed it last night, but I'm certain this guppy is still a bit unhappy. I've read about constipation (and feeding peas) and about using salt treatments, but I'm not quite sure what the little guy has. He's eating and pooping. There are no white spots, red spots, scratching along the gravel...just looks jittery and is swimming tail down. All the other fish seem quite fine. I think I might be pushing the overstocked limits, but these fish seem(ed) fairly well conditioned to the environment, except when I went 4 weeks with only 2 water changes. Well, I've been obsessing over your site and over my fish. Any advice you have would be most welcome!! Thanks, Lynne in San Francisco <Lynne, part of your problem is that the tank is far too small. A 10-gallon tank isn't useful for Guppies, and certainly not in conjunction with Corydoras and tetras. In very small tanks you have an uphill struggle to maintain a steady pH, adequate oxygenation, and above all reliably good water quality. For the fish you have, a tank not less than 20 gallons would be essential. Period. End of discussion. Trying to recommend "fixes" for this tank are akin to rearranging the deck-chairs on the Titanic. In terms of specifics, your Guppy likely has something called the "Shimmies", a neurological complaint apparently related to water quality and water chemistry problems. When livebearers are stressed, they often react this way. Behaviours including rocking from side to side, treading water, and other odd swimming movements. Improving water conditions will help, though there's no treatment as such that can be guaranteed to cure it. Just as a reminder, Guppies are classic hard water fish, and you're aiming for a pH of between 7.5 and 8, and the hardness should be upwards of 10 degrees dH. Adding 3-5 grammes of marine salt mix (not tonic salt, not aquarium salt) per litre will dramatically improve their health, though tetras and catfish should not be kept in a tank with brackish water. If you cannot move the tetras and cats, then don't use marine salt mix at all, and instead concentrate on raising the carbonate hardness by incorporating some calcareous media (e.g., crushed coral) in the filter, but use small amounts at first so you don't raise the carbonate hardness, and thus the pH, too far or too quickly. Just a reminder: adjusting the pH isn't the aim here, so don't go pouring pH potions into the tank; livebearers care about carbonate hardness, which would seem to be low in your tank if you have a pH of 7. Cheers, Neale.>

Re: Guppies - male swimming funny 03/03/09 Thank you for this response. I really appreciate getting your advice. <You're welcome.> I'll try the coral to see if that helps. <Don't confuse a media bag filled with crushed coral with just sticking a dead coral into the aquarium! A dead coral will not have the desired effect. Water has to be flowing past the crushed coral under pressure to absorb the calcium carbonate fast enough. For a 10-gallon tank, I'd be trying maybe 1/4 to 1/2 a cup of crushed coral in a media bag (the foot of an old pair of nylons works fine). Stick this into the filter, and off you go. If you have an undergravel filter, mix the crushed coral into the gravel. But again, just dumping crushed coral in a regular gravel substrate won't work either; there needs to be water flow!> I've been feeling like the tank is too small too, but was advised as such by the fish store. <Oh.> I'll be considering getting a new tank then. <Make sense. Saving a couple bucks getting a 10-gallon tank is invariably wasted by the dead fish, medications you end up having to buy. It's a fool's economy. A 20-gallon tank will absorb a lot more punishment before things go wrong, and is easily the best recommendation for casual aquarists. Who don't want to be fiddling with dead fish all the time.> Thanks a ton. Lynne <Cheers, Neale.>

Livebearer beh. and hi there, can you help with a couple of questions? <Will try.> firstly can tropical fish eat earthworms from the garden?  2/4/08 <Yes, assuming your garden is "organic" -- any pesticides used, and even some fertilisers, are deadly toxins to fish. If in doubt, don't bother. But earthworms make a great food for mid- to large-sized predators.> also I have just added 3 silver molly (1 male, 2 female) to my tank of 6 platy, the problem is that one specific platy (he's about 2" long with a huge dorsal fin, so I assume he is mature) well he is quite intent on chasing the mollies around the tank basically all the time, he will chase both the male and the female, is this normal or is he being overly aggressive, <Absolutely typical. I'm guessing your tank is relatively small (less than 200 litres) in which case males of all livebearer species can be assumed to be more or less aggressive and intolerant of other males and unreceptive females.> the ratio of the platies is the same as the mollies 2-1 so he is not starved of females. <While it always helps to have more females, this really only becomes effective when you have big schools of fish in nice roomy aquaria. If you have just half a dozen livebearers in a small aquarium, the males can be troublesome.> any advice would be great, cheers! David <Please send a message with capital letters next time! It's one of the house rules for the benefit of other readers, not all of whom speak English natively, and rely on good grammar to make sense of things. Cheers, Neale.>

Male Guppy chasing Male Platy 09/08/07 Hi, I have a 65 litre tank with 4 Neons, 1 guppy (two recently died), 5 platies. My blue spotted platy is constantly being chased by the yellow male guppy. The guppy never chases any other fish on the tank. It seems to be attracted to the area near the anal fin and seems to reach for that area or just chases it around everywhere. I have checked other sites which say that the platy could die from stress caused by constant chasing or is ill (but I am pretty sure it is not ill as I can't see any symptoms of illness). What should I do? Thanks. Regards, Seema <Hello Seema, There is, unfortunately, nothing you can do about this. Male livebearers are "programmed" to always be trying to make with females and chase away rival males. Evolution has pushed them towards a "live fast, die young" strategy, compared with the females, which are usually bigger, slower growing, and better camouflaged (at least in the case of the wild-type fish). Indeed, with guppies particularly females choose males with the brightest colours, apparently because any male that survives to maturity with a brightly coloured tail that attracts predators must have good genes. To compensate for this, male guppies will try to mate with everything and anything they can, because as far as their genes are concerned, tomorrow they could be eaten! In the wild, guppies prefer guppies, platies prefer platies, and so on -- but in the aquarium, where there are no alternatives, male guppies will attempt to mate with almost any other kind of female livebearer, as well as chase away any other kind of male livebearer they deem a possible rival. In other words, there's nothing you can do about this behaviour other than either [a] remove the male to another tank; [b] add two or more female guppies so he chases them instead; or [c] move them all to a bigger tank with lots of plants so the fishes can separate themselves and hide if they want to. Cheers, Neale>

New Fish   8/20/06 Hi, <<Greetings, Susan. Tom>> 3 days ago I got 6 platies, in a 10 gallon tank. They seem to be very aggressive with each other. Only two of them, but before it was only one. <<New environments/conditions can bring this type of behavior out in some fish, Susan. A little early to tell if this is a "permanent" situation, though. My Sunburst Platies go through "phases" where they'll exhibit this type of behavior only to quit and go back to their normal activity, which is looking for me to feed them. :)>> I feel bad because the other fish seem to be scared of them now. <<Again, Susan, a bit early to tell.>> The two fish are both females (I have 2 males and 4 females) and one of them seems to be picking on only one, and the other one is picking on the rest. But they won't pick on each other. They all seem fine, they look fine, I don't know why they're doing that. <<Could be establishing a "pecking order", of sorts. Other factors may be involved here, however.>> And another question: I'm not sure if one of my aggressive females is pregnant, but she had a bit of a bigger belly then some of the others, and she has a blue gravid spot. <<With 'livebearers' such as Platies the females, almost invariably, are either pregnant or on their way to being so. Females are capable of storing the males' sperm inside of their bodies so they needn't mate every time in order to give birth. A single female, isolated from any males, can give birth three or four times (perhaps more) once she has mated. The fact that your female has a larger belly with a darkening gravid spot indicates that she's, almost certainly, pregnant.>> She has a blue color to her, so is it just a beauty mark or something? The "gravid spot" is inside of her, so is it possible that she is? <<I'd say this is not only possible but probable. On a side note, females close to giving birth won't be very tolerant of other fish, particularly the males. They prefer solitude and quiet (understandably) while the males have only one thing - besides eating - in mind, if you see where I'm going with this. Boys will be boys... :)>> Thank you for your time. Please respond as soon as possible this is very urgent for my fish. -Susan <<Keep in mind that all of your fish may look a lot alike but, won't necessarily behave alike. A dominant female may be showing the others, male and female alike, that she's going to "rule the roost" especially where mating is concerned. Usually, it's the males who pester the females practically non-stop but you might just have a couple of ladies who don't "play that game". Not at all uncommon, really. Keep an eye on them. If you have one that seems to pick on the others just because she likes to, she might have to be isolated. In the meantime, I wouldn't be too concerned. Best regards. Tom>>

FW Pecking Order   2/22/06 Thank you so much for your prompt advice.  I now seem to have a new problem. The death of my (slightly aggressive) male molly seems to have upset the pecking order in the tank.  My three male guppies used to get along swimmingly, hanging around together as a defense against getting picked on (presumably).  With the molly gone, the two biggest guppies are turning on the smallest and bullying him, and he is losing his beautiful tail, not to mention the fact that he no longer swims with the other two.  I understand the behaviour, but don't know what to do.  He will be gone by the time I quarantine another fish to help balance out the aggression.  Is he doomed to die?  And if he does, will the largest one then turn on the second largest and kill him too?  Help! Kathy <Move all the rocks and decorations around to new locations to set up new areas, then lower the water temp to 77 F to reduce their metabolism. Add a clump of floating plants or ABS black plastic pipe to establish a refugium for sick or injured fish to hide in.-Chuck>

Mollies Hello, We have a small (15 gallon - high) tank with three mollies in it. It has UG filtration and an airstone (at bottom). Curious thing: The mollies are always at the very top of the tank, something I have never seen before I moved them from a standard all glass 10 gallon tank. <Hi Thom, Lorenzo Gonzalez replying for Bob-in-Indonesia... Mollies and their kin (guppies, platys, etc.) are surface fish by nature, just look at the shape of their mouths. Just right for eating insect larvae off the surface... A little factoid for your museum, your Mollies are a close relative of the 'mosquito fish' cultivated in some parts of the world to combat mosquito-borne plagues... Anyway - the new 15 high is quite a bit deeper than their old home, and unless there's interesting stuff throughout the depth of the tank, they really won't explore much...> I'm writing as I just came across "Ask Robert Fenner a Question" and thought I might.  Thanks, Thom Smith, Curator <Any time. Bob will be back from safari in about 10 more days. I've been answering his 20+ daily emails for several days now... boy is it hard, but rewarding labor! Regards, Lorenzo> THE BERKSHIRE MUSEUM Check our site: http://bcn.net/~aquarium/Museum.htm

Guppy and Starfish Questions Hi there! <Cheers.. Anthony Calfo in your service> I seem to be emailing you on a weekly basis these days (sorry) but the more we get into this hobby the more strange and unusual things happen! Anyway, my first question relates to our tropical tank. One of our guppies has got the hots for a silver colored platy.  <what a cheeky little monkey> He pursues her around the tank relentlessly, trying to make her see just what a God's gift to fish he really is, while she plays hard to get! I assume that this relationship is doomed and he will suffer forever from unrequited love.  <are you still talking about fish  or do know my high school sweetheart?> However, if they do manage to get it together what will the results be? Gatties or Pluppies?  <actually a fish that looks like Buddy Hacket with a tail> Or could there be another reason for his amorous advances? <sure... he may just wants to cuddle...hahahahahahhahhahahhahah! Ahem, I mean...no, I think you've got the general gist of his intent. They may not even be able to produce viable offspring/hybrids> My second question relates to our reef tank. One of our Fromia starfish seemed to expel something from its underside the other night. It was orange in colour (same colour as the starfish) and resembled two hands (or two starfish even) stuck together. It measured about 0.75cm wide and 0.5cm high. It was carried around in the tank by the current and settled briefly on some live rock before disappearing into the reef. The "legs" didn't appear to move during its brief stay on the live rock. Have you any idea what this thing is? <under stress...some echinoderms do release part of their innards. Perhaps this is the case, but I honestly have no clear idea> This hobby just gets more and more fascinating! Thank you for all your help! Lesley <kindly, Anthony>

Swordtail Disappearing Act? Hi there I am new to this so I was wondering if you can help.  <<Hi, I probably can. Hopefully in time!>> I recently purchased 5 swordtails 3 male 2 female (did not know this till I got home). This morning all was ok, this afternoon one of the males has disappeared without a trace.  <<Very likely driven right up OUT of the tank by one of the other males. Which, by the way, really must be returned for another female, or things could get very ugly for the girls.>> The swords are the biggest fish in the tank are all males are similar in size. Where has he gone and has he been eaten? Jim <<Check around that tank VERY carefully - cannot stress/emphasize how easily fish get into the smallest places. If you find him in time you might be able to revive him. I feel he has MOST CERTAINLY been driven out of the tank. Check even the weird places. If he just died in there you would see the other fishes nibbling on his rotting corpse. Marina>> 

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