Minimum Tank Size: 10 Gallon (Short-finned Molly), 20 Gallon (Sailfin Molly)
Care Level: Easy
Water Conditions: 6.5-8 and Moderately Hard to Very Hard (Short-finned Molly), 7.5-8.2 and Hard to Very Hard (Sailfin Molly)
Temperature: 72-82 F (25-28 C)
Maximum Size: 4 inches (10 cm) Short-finned Molly, 6 inches (15 cm) Sailfin Molly
Mollies are one of those most popular fish in the aquarium hobby, and most people have had at one time, at least one of these gentle and attractive live bearers in their fish tank. Most people mistakenly believe that there is only one species of molly available in fish stores, but there are actually three separate species available in the aquarium trade. However, at this point, most of the mollies available are so hopelessly hybridized, that it would be impossible to determine which species they originated from.
If you ever come across wild mollies in a fish store, they will usually come from one of two species. The first species is sailfin mollies (Poecilia latipinna) which are found in the coastal waters of the southeast United States and around the Gulf of Mexico. These are among the most common type of molly, and are incredibly prolific breeders in the wild. Because they live in coastal regions, they have a high tolerance for brackish water, and have even been found living in the ocean.
The other species that is commonly found in the aquarium trade is the short-finned molly (Poecilia sphenops). These fish are found in Mexico, Central America and in the northern parts of South America. The short-finned molly adapt most readily to the home aquarium, and is one of the easiest beginner fish available . Like their sailfin molly relatives, they can also tolerate high salinity in water, and do well in both brackish and freshwater tanks.
There is a third species of mollies that is occasionally found in the aquarium hobby, but it is far rarer than either the short-finned molly or the sailfin molly. It is the Mexican sailfin molly (P. velifera), and is very difficult to breed and keep in aquariums, though it does well in outdoor ponds. It is found in the wild in the coastal regions of Yucatan in Mexcio, and like the other two species, tolerates a very high level of salinity in the water.
Housing Molly Fish
The short-finned molly is undemanding when it comes to providing them with an aquarium, and most will happily live in a 10 gallon aquarium. But if you really want them to thrive, they should be provided with at least a 29 gallon long tank.
Sailfin mollies on the other hand, grow much larger than their short-finned cousins, and require a minimum tank size of at least 29 gallons. But like many other large fish in the hobby, the fish will do much better over the long run if they are provided with a large tank right off the bat. Larger tanks also have the benefit of offering a more stable environment for the fish, since they aren’t as prone to the sudden water quality fluctuations that smaller tanks suffer from.
All of the species of mollies that are commercially available are docile fish, and will do well in any peaceful community tank. And emphasis should be placed on the word peaceful – if there are any aggressive fish in the tank, the wide-bodied and passive mollies will be bullied mercilessly.
When it comes to filtration, mollies do much better when the tank is over-filtered. They aren’t necessarily a messy fish, but some of the hybrids are more susceptible to disease than some of the other beginner fish, and do better when living in well maintained water. The best filters to use are either a high quality hang-on-back filter, or a canister filter if you can afford the hefty price tag that comes with it.
I would strongly recommend choosing an Aquaclear Power Filter for a molly tank. This filter combines excellent filtration with a durable design, and it will keep your tank sparkling clear for years to come. You can also read the Aquarium Tidings Aquaclear Filter Review here.
One question that comes up often with mollies, is “do mollies need salt in their water?” The answer to this question isn’t simple, and a lot depends on what species of molly you have. As with most fish, mollies do benefit with some aquarium salt in the water, but nothing has conclusively shown that mollies need to be kept in water with salt added. In fact, most mollies will thrive in a completely fresh water aquarium, with absolutely no salt added.
The myth that mollies have to have a large amount of salt in the aquarium likely stemmed from some of the hybrids being more sickly than other types of fish. Like any fish that has been over-bred (neons come to mind), the genetic line can sometimes be weakened, and the fish become more susceptible to diseases. Many people then falsely attribute the illness to a lack of salt, and a myth is born.
I have kept mollies for close to a decade now, and they have never been in a tank with any salt added. Aside from one minor disease outbreak a few years ago (from an improperly quarantined fish), they have always been healthy and have had no problems breeding in large numbers. In fact, many of the mollies that I currently keep, are descendants of the original mollies.
Feeding Molly Fish
In the wild, mollies are omnivores and feed on small invertebrates, algae and plant matter. In the home aquarium, they should be fed a high quality flake food, and a variety of vegetables. One of the best prepared foods that you can feed them is Hikari Micro Wafers. Their favorite vegetables are blanched zucchini medallions, cucumber medallions and shelled peas. If you don’t have the time to cut and blanch vegetables, then a spirulina based pellet or flake can take the place of plant matter in their diet.
In order to get them into breeding condition, they should also be fed live or frozen foods as a treat. Their favorite frozen foods are bloodworms, daphnia, and brine shrimp. They will also greedily accept any live foods that you can find to feed to them, with live blackworms, bloodworms, daphnia and brine shrimp being special favorites.
Breeding Molly Fish
The molly fish is a live-bearer, which means that its eggs are internally gestated until highly developed fry are born. Because it’s doesn’t scatter its eggs, there is usually a high survival rate among its fry (as long as the tank doesn’t have any large predators).
Like most other live-bearers, breeding mollies is incredibly easy. It really boils down to fish + water = hordes of babies. But as with other easy to keep live-bearers like guppies, you have to be careful what ratio of sexes you keep in the aquarium.
In any aquarium that contains both male and female mollies, you should try to maintain a ration of three females to every male. Male mollies will relentlessly mate with any females in the tank, and if their attention isn’t divided between several females, then the female they focus on will eventually become highly stressed and may even die from the constant mating attempts.
If mollies are in a community tank, then the best way to ensure some of their fry survive is to add some floating plants or some dense plants like Java moss. While the babies are born highly developed, their small size will still allow for larger fish to eat them. The more plants that an aquarium has, the better chance that some fry will reach adulthood. Floating plants are the best choice, as fry can easily hide from adult fish in the dense vegetation near the surface.
Madison says
Does anyone know something that would stop a male molly from always (literally every 5 seconds he starts again) chasing a female molly? They had babies a while ago but the male still chases the female. I recently moved him back to the main tank after a vacation in my sisters tank to hopefully make him forget about causing trouble… What should I try now?? The”Vacation” helped him and his tail looked a lot healthier but he’s still a trouble maker.
Nicole says
@Madison: I had trouble with my female dalmation molly. She was bullying all my other fish, chasing them around, nipping tails and being a real pain. My local pet store told me to try upping the temperature and feeding a little more often and it worked.
My community now gets fed every morning and evening and the temperature is a constant 28c. This has worked wonders. I also add a little aquarium salt, keep it aerated and adding Special Blend Microbe-lift and Tetra Easy Balance along with weekly water changes helps keep the water quality perfect.
NO MORE MOLLY TANTRUMS 🙂
Robert Brand says
That’s interesting that that worked to calm down your mollies. I’ll have to try the multiple feedings in the future to see if that calms down the molly fish that I keep.
Tadgh says
I have three pregnant mollies and 2 males but for some reason one of them spits out there food and the male still chases the pregnant fish
Godzilla1234 says
Maybe she doesn’t like the food and the male fish is chasing the female because he is trying to mate with her. If it gets worse, remove the female and put her in another tank. The reason may also be not enough space.
janjan says
How long does it take for a Molly fish to mature- when will babies born today reach adulthood?
Robert Brand says
They’ll be sexually mature at around 5-6 months old, though they won’t be full size by then.
janjan says
Thanks, Robert. I couldn’t find that anywhere. Some of my newest babies are surviving in the tank with the adult mollys. I’m keeping them well fed, and the babies have lots of live plants to hide amongst. They’re hanging out with my one month old juveniles – safety in numbers, I guess.
Robert Brand says
I’ve always find the schools of baby mollies to be fun to watch. I’ve had pretty decent success keeping fry in a large tank with the parents in the past, and it does seem that plants are key to their survival. That and the other fish that they’re kept with.
Emilia Bieth says
ive kept my babies in a separate 2.5 gal tank. so far i have 5 babies living.
gaz says
Mollies are NOT gentle peaceful fish. This is a misconception that other fish owners and petshops promote. Mollies will become aggressive towards each other in tanks esp the males towards females and chase them to breed non stop. Male mollies will try to wear each other males down to assert dominance, the weaker ones becoming stressed and often sick. These fish also have a habit of bullying other tank mates esp at feeding time and it has been observed and recorded that Mollies ‘pick’ at the protective slime coating on other fish. They also tend to rip apart or eat most plants except for the toughest eg Java Ferns. Also, (as they require a certain type of water quality) susceptible to diseases such as ick and fungal diseases esp sail fins and blacks. A large single species tank is recommended, with maybe a FEW tetras or larger dominant fish that can handle themselves.
Robert Brand says
It’s actually clearly stated in the article that male mollies will relentlessly attempt to breed with the females, and you should keep appropriate numbers of each sex in order to keep aggression down.
As for them being peaceful fish, I would say that in my experience the vast majority of short-finned mollies are peaceful, and the most sailfin mollies are as well. The only aggression issues I regularly hear about are directed towards similar species of fish (platys, swordtails). Although I have occasionally read about aggression towards large, docile fish like goldfish, but let’s face it – these two species should never share a tank based on their temperature preferences. Ignoring goldfish, they should peacefully co-exist with most of the more common community fish. The only time you may experience aggression issues is if you keep a lone male, but even then most of the time they remain relatively peaceful.
And I will agree that they can play havoc with plants if they are hungry. Though I’ve never heard of, or seen them go after a tough plant like Java ferns. I will say that I’ve often seen them take small pieces of soft leaved plants like hygrophila polysperma, water sprite, water wisteria, etc. But this usually isn’t a major problem unless you big into aquascaping.
Edit: Though I probably should have added that any fish has the opportunity to become aggressive. If they are kept in cramped conditions, or the balances of the sexes are out of whack, they can become aggressive towards other fish. Also, sometimes the personality comes into play, and you may experience behavior that can only be attributed to the fish being naturally aggressive. Still, if the mollies are kept in spacious aquariums, with the proper balance of sexes, you shouldn’t experience much in the way of aggression.
Jan says
I have a small ten gallon tank with mostly jollies, and three neon tetras. I had an orange lyre tailed Molly when I inherited the tank in June, who would constantly harass the others, one female in particular. And a super sexed black Dalmatian male sail fin Mollie who chased my white Molly around constantly trying to mate. She had babies twice in six months. Most are white or mostly white Dalmatian she was very peaceful she died recently when I had a problem with ammonia. The nasty orange lyre tailed Mollie, I killed by accident when cleaning the tank. Good riddance!! But I would have preferred to give her away. I’m overstocked with mollies right now and am trying to give some away to elementary schools in my
area.
Robert Brand says
It’s certainly tough keeping mollies in under-sized aquariums like that – especially when you have a few aggressive males. Hopefully you can find some homes for them. If you can’t give them to school, there are often local aquarium forums where you can give fish like that away. You should try looking it up for your area. Also, while they may not be interested in crossbreeds like you have, some local fish stores will often take fish off your hands for free.
Georgia says
I’ll have them if you need rid, I have never had any issue with my mollie’s they are lovely and get in with all my fish ( ranging from fighters to puffers catfish sharks etc) all happy to live with each other in a 280l tank
Wolfman🐺 says
I used to have them they die after spawning but the babies will be swimming around.
Sarah Henderson says
I recently acquired some beautiful sailfin mollies of which one was very pregnant, I placed the fry in a “nursery” within the aquarium however I am wondering if there is special food for the fry or should I grind the flake food for the adults very fine and use that? Any advice would be greatly appreciated. Thanks in advance.
Robert Brand says
Luckily, molly fry are born large enough that finely ground flake food will work fine for them. If you want to put in some extra effort, they will also appreciate baby brine shrimp when they’re new born. You could also purchase one of the many fry foods out on the market, but it’s really no necessary.
SARAH HENDERSON says
Thanks so much not only for the advice but also for answering so quickly. I am really looking forward to watching them mature and grow into beautiful fish like their parents. 🙂
Luca says
Hi guys, I have a very “fat/pregnant” molly and was wondering how long will she stay this way before the fry are born? I got her about two weeks ago from a pet shop in the oversized condition and have had her in a separate breeding net since, but have had no action. Are there signs to look out for and could I put her back in the general tank till then? Thanx
Robert Brand says
Gestation for mollies is usually around 28 days, and I’ve found that moving them into a breeder net can occasionally slow that down a little bit. I’m not sure if it’s due to stress or not, but it does seem to delay it a little bit. You can usually tell how close she is to birth, by looking at the gravid spots (the dark spot near the anal fin). If your fish is naturally light coloured, and this spot is very dark, then she should be close. It’s harder to see on dark coloured fish though.
I would just leave her in there for now, and make sure she’s well fed, and the water is kept in pristine condition. Sooner of later, you’ll see hordes of tiny fish fry.
Luca says
Hi M,
Thank you for your response. Fate would have it I found 11 or so little fry in the breeding net the next morning. I left her in the net for the day and then moved her into the main tank. All seams fine.
Robert Brand says
That’s great news. Good luck raising the fry and hopefully they all make it to adulthood.
HOLLY H. says
Hi, I have had Dalmatian Mollies for about 3 years now. I started out with 2, which I later found out were a male and a female. I had them in a 5 gallon tank. Almost a years later the female gave birth to 6 babies (at least that is the count I had after several attempts to count them. I quickly moved the new family into a 10 gallon tank, once the babies were big enough to moves safely. They stayed in the 10 gallon and the babies grew up well, the original female died during labor with her second batch of fry (I know this because she was shaking back and forth just like she did before delivering her first set) when I took her out of the tank. Anyway those babies grew up and had babies, etc. I have read everywhere that the adults will sometimes eat the babies, but I have never had an issue with this. The adults usually leave the fry alone. I had the ever growing population in a 10 gallon tank (I could not afford a 20 gallon just yet) and over the years a few have died due to likely overcrowding conditions in the tank. Recently my brother-in-law gave me his 65 gallon tank and when I moved the fish I found that I had 49 fish in that little 10 gallon. My fish are much happier having enough space to move around in and since the move, 1 of my females has had 2 litters of fry 1 litter is barely a month old and the new babies are just a few days old. Her mate chased her relentlessly after giving birth, but has since calmed down (he seems to prefer her over any of the other females in the tank). I have only had 1 fight in my tank (that I know of) and an EX-dominate male was challenged and lost to a young male and lost. He had a swollen eye and some smalls nicks in his tail (I looked for signs of disease and found none) but he quickly healed. However something very strange happened then, he changed and soon became a female. I looked it up and found that this can occasionally happen if there are not enough females of breeding age in the tank. By the way, the babies have plenty of hiding spaces, as I have made caverns out of coral and shells.
Robert Brand says
It sounds like you have quite the school of mollies now, and they must be happier in the new tank. I hope things keep going well for you and your fish.
Heather Dawn Hillhouse says
Recently my fish started dying after an algae treatment so I changed water and filtered like crazy. All parameters were good and fish that normally were active and came straighto to the front when I fed them were hiding and lethargic all the time. Suddenly one would zip across the tank and die instantly. 🙁 Now I have a tiny platy and a huge pleco left in my tall 15 gallon tank. Help, my fish are like my babies
Robert Brand says
I know many of those algae control products state they won’t harm fish, but I’ve known many people who lost nearly all of their fish after using them. I’m not sure of the reason, but I’ve heard some people claim it sucks all the oxygen out of a tank. But I have nothing concrete to back that up – I only know they tend to kill fish.
I would continue to do large water changes every day, and try to further oxygenate the water by adding an air stone, or something along those lines. Hopefully with fairly large water changes every day, it will remove what is killing your fish. Also, make sure you add a charcoal insert to your filter, as that would also remove any toxins from the water.
Imasillylady says
Don’t use algae treatments. The other commenter is right. It takes all oxygen out of the tank. Killed almost every single fish I had. I now use a uv light for the tank. Keeps it clear.
Roselyn M. says
I have dalmatian molly that likes to swim I say upside down or with it’s tail up. It just started doing this. What does this mean and is it bad?
Robert Brand says
It’s probably a problem with its swim bladder. Try lightly boiling some peas, then let them cool. After they have cooled, remove the shell, and feed the peas to the molly. Make sure the fish can reach the peas, as sometimes you will have to feed it by hand. Don’t feed it any other food for a day or two while doing this, and some people recommend letting it fast for a few days first. I find fasting generally isn’t required, but to each their own. This will often clear up the problem. Also, increase the temp to around 80F (26 C) for a few days – but only if the other fish in the tank can handle it.
If that doesn’t work, and the fish is still exhibiting signs of illness (clamped gills, not eating, etc), then you should try antibiotic food. This will usually deal with whatever is wrong with the fish. But it’s best to try the peas first.
Heather says
Hi. After keeping goldfish in a large tank for years, I now only have a 25 gallon tall. Just got 2 silver lyretail mollies last night and they are picking at each other already. The fish guy thought they were both females. I think one is a male though. My brother said these were mellow fish but most comments here say different. Should I get 2 more females to help as suggested here? Take back the male and get another female or two? Or is another tropical fish type better for calm watching and stress reduction? Would feel bad catching the babies to give away too. Advice? Thanks!
Robert Brand says
The problem you have is that you’re really too small for mollies, and mollies and goldfish don’t mix. Mollies require tropical temperatures, while goldfish require coldwater, and they will start to suffer if they are kept in warm temperatures too long (usually due to lack of oxygen).
Right now, I would recommend keeping the goldfish alone, but if you’re dead set on adding more fish, I would stick with something cold water like white cloud mountain minnows, or maybe rosy red minnows (although these are known to be fin nippers sometimes). Also, before buying any smaller fish, make sure they are larger than your goldfish’s mouth, as the goldfish will still try to eat small fish.
Heather says
Hi Robert. Thank you for the response. I guess it wasn’t clear that I used to have goldfish but not anymore since I had to downsize my 75 gallon to a 25 tall now. I have a tropical setup with wood and plants and 2 otocinclus catfish. Tank has been setup for 6 months. Added a nerite and the 2 mollies. The female who didn’t look pregnant dropped some babies it seems. Saw 5. So my tank is too small for mollies? Should I take them back then and get something else? I feel a bit bad doing that but want the fish to be comfortable. I know this tank is too small for goldfish really.
Madison says
I need your help!
I have a 36 gallon tank. It’s 80% mollies- I can’t exactly count them because a lot are still fry.
One of my females has some sort of infection. She is shimmying a bit. Her side is white and red, it looks almost flaky. There are dents or holes with appear to be left by missing scales. Her gills are red and inflamed. I have seen ich in mollies before, and this is certainly not it- there are no white dots or cottony growth. There is no exess slime or flashing that I can see. Other fish have been picking on her, so I moved her to another tank.
I am very worried because I am going out of state for a week and have to leave in a few days. My family isn’t the best with fish, they are grossed out/scared of them, and it would be heartbreaking for me to come back to a dead molly.
Other forums suggest a vet or a scraping to determine the bacteria causing this, but those take a while and I’m running out of time!
Roz says
Sounds as if your Molly has ick or a fungus. Go to the pet store and buy API fungus cure, the only thing is that it will take up to four days and new filter to work. Good luck.
Robert Brand says
If there are no ulcers, then it sounds very much like gill flukes. They are somewhat similar to ich, and cause almost the exact symptoms you’re describing. You would need to pick up anti-parasite medication, and check your water. It usually only has outbreaks when the water isn’t perfect, or the fish are overcrowded.
If there are ulcers, then it’s more likely bacterial, and you would want to pick up a food antibiotic. It generally does internal damage to a fish though, so you may not be able to save the infected fish at this point.
Madison says
She died this morning, although I will use your advice to make sure no other fish gets the infection/parasite. I didn’t see an ulcer, but I have pictures- I’m just not sure how to post them here. The fish may be overcrowded. There are lots of fry that need rehoming. Thank you for identifying the issue.
Robert Brand says
I’m sorry to hear you lost your fish. And that’s one of the biggest problems with livebearers – they breed so fast they can overrun your tanks.
librarose says
Know anyone who wants baby Molly fish ? I have a lot of them 2 weeks old for free !!!
Robert Brand says
You should tell people where you’re located. People come from all over here. 🙂
Kristopher says
Me and my cuz that live toghter will take them if u deliver 5 north Baltimore st Franklintown pa where are you located
usagrammy says
being a recent owner of a pr of mollies, who had 5 fry 2 days after purchase, I read all ur comments, which r helpful. my caregiver put the fry in a nursery mesh basket. I have 3 aggressive barbs and wonder when it’ll be safe to release the fry. I have a 50g tank, with 3 zebra tetras, 3 barbs, 4 neon tetras, the 2 mollies and Harriet my blue lobster. I’m concerned about overcrowding. should I just give away the fry?
Robert Brand says
You’re not even close to overcrowding yet, so I wouldn’t worry about that. Depending on the size of the basket, you probably want to wait until the fish are close to the size of a dime, though this won’t work with smaller baskets. If the basket is too small, then wait until they’re larger than the fish’s mouths. If they can’t fit the fry in their mouth, these species won’t eat the fry (though that’s not true for all fish).
But I would be a little more worried about the lobster. It might aggressively hunt down the smaller fish.
usagrammy says
thank you Robert. actually the lobster Harriet, doesn’t seem to bother with any fish. she’s too busy re-landscaping and tearing up my plants. she’s a hooligan, but fun to watch.
Robert Brand says
Crayfish are an amazing pet to watch, and immensely underrated.
Kristen says
Hi, I need some tips and advice please. I just brought home 3 Mollies today, (our first fish) 1 male and 2 females. We have a 10 gallon tank, and they are the only fish in it. My biggest concern is that they will mate (I’m sure it will happen) and the babies would get sucked into the filter. I would like advice on what to do when the females are pregnant, and also just general Molly care tips. TIA
Robert Brand says
There are a few things you could do. You could get a breeding net for when the female becomes very heavy with babies. Or you could cover the intake with some sort of netting, or a sponge so the fry can’t get sucked up into the filter.
Beyond that, you don’t need to give pregnant mollies that much more attention. Just keep on top of water changes, and feed them high quality food, and you should be fine. If you don’t have any life plants though, you might want to consider adding them. Floating plants, or dense ones like Java moss make a great place for the fry to hide.
usagrammy says
hi Kristen, you need a nursery cage that you install at the top of your tank. make sure after putting it together, to rinse cage in purified water before adding to your tank. crush flakes when feeding fry. enjoy.
Holz says
How to know when my mollie is having a baby
Robert Brand says
It’s pretty simple: they go slightly nose down, and fry will start to appear. There’s not much more to it than that.
Lee McIntyre says
Can I just have 2 male mollies together in a community tank or do I have to have females too.
Robert Brand says
If you have a large enough tank, then it should be fine. The males are prone to sparring, but in larger tanks, it will rarely ever become a problem. And by large, I mean greater than 29 gallons.
Lee McIntyre says
Thank you so much for your reply. My tank is just over 50 gallons.
Sandhya says
Hi, I have a 20 gallon aquarium. Initially when I set it up got African chichids, coz of their aggressive nature each one started to beat one another to death. So I gave them all and got molly. Had done a full tank cleaning 15 days back, clean the filter system regularly and did a 10% water change before adding the Molly. For one day it was fine and all of sudden the water has become dusky and cloudy. The filter system is working fine with good amount of aeration. My pet shop fellow advised to add salt and have done the same now. Not sure what went wrong, pls advice..
Robert Brand says
It sounds like your tank is cycling again. Bacterial blooms are quite common when the water quality is poor, and for some reason, your tank’s filter must have had the bacteria disturbed. The best way to combat this is by putting lots of fast growing plants in the aquarium. The ammonia and nitrites levels are probably well in the danger range (not that there’s really a safe range for these), and you need something to combat it fast.
Plants like hornwort, anarcharis, duckweed, and several other plants will feed on the ammonia and nitrites, and will help to get your aquarium through the new cycle. You can also use products like ammonia lock, but I find it just extends the cycling longer, which does damage to your fish, and shortens their lifespans.
Shari Roe says
My female is giving birth every two weeks! I have so many babies I don’t know what to do with them. I have never seen anything like it.
Robert Brand says
I know that feeling. lol
HOLLY H. says
I feel your pain, I too have a tank full of baby mollies. They are breeding at a crazy rate. I have a couple of females that are giving birth back to back. The males go after them right after they give birth. I actually feel sorry for the females having to be constantly pregnant without a break in between. I have actually had a few baby deaths recently when they end up getting in the way when the males are chasing the females for mating. I have over 60 mollies in a 65 gallon tank and no matter what tank they have been in, they simply multiply until they end up overcrowding it.
Dani says
I had 3 baby creamcicle lyretail mollies. One started sitting on the bottom of the fry net and would move around like it was too heavy to lift off the bottom and it died the yesterday. Now another one is doing the same thing. Water is good. All other fish in the tank are fine. I have tested my water. Ammonia nitrate and nitrite are 0. The tanks has been cycled and running for a few months. I cannot see anything visibly wrong with the fry and they are a week old. I have the two left and one baby is still swimming actively. Any ideas would be appreciated
I have raised mollies before and never had anything like this.
Robert Brand says
I would retest your water first, because if nitrates are showing at 0, then there is something wrong with the water. Also, I would test the pH is that’s an option for you. Then I would do a large water change just to be on the safe side. That would rule out most of the easy stuff.
Then we move to the more difficult stuff. Is there any change in their poop? Any discolouration on their bodies?
Dani says
Well the test strips are by color, so I probably misread. I retested in better light this morning. Looks like the nitrate is above 0 but less than 20. As far as discoloration goes I can’t tell anything. They are light colored anyway. Poop looks normal as far as I can tell. I only have one left now and while it still swims freely it is starting to hang near the bottom of the net and I’ve noticed it seems to be trying to rub its sides on things. The adult fish in the tank look fine as well. The water is fairly hard and ph is around 7. My cory cats laid eggs yesterday though so I know the temps probably drop at night but my heater is set at 72
Sheri Winkler says
I love mollies and have had Dalmatian mollies in the past. I just set up a 20 gallon tank and am wondering if anyone on this thread is in Chicago as I am. I’m looking for Dalmatian mollies.
Leah says
Hi everyone. I’ve got a balloon molly but she looks pregnant. Any tips on how to make sure?
Robert Brand says
Aside from the very obvious swelling, you’ll notice a black spot near the anal fin: This is called the gravid spot. If she has the black spot, then she is definitely pregnant.
Jjustine says
Hello. My friend recently got me a single black molly for my birthday. When she came over- the fish food was goldfish flakes. Is this okay for the molly? How long can it last with goldfish flakes? If not, what should I get?
Robert Brand says
Goldfish flakes should be fine, unless they’re pure spirulina or something similar. They’re close enough to regular flakes that it shouldn’t be a problem. As for how long it will last, it should last a very long time with a single molly. Only feed it as much as it can eat in 3-4 minutes. It’s usually not much more than a small pinch.
giftnel ruiz says
what molly fish breeds the most?????I’m going to buy some
Robert Brand says
They all breed about the same, although some of the more ornamental ones like balloon mollies do occasionally have problems. You’re pretty safe with going with the ones you want, and they will breed quickly.
HG a o says
Why does it seem like every time I just look at my balloon mollies, they die? We’ve checked the water in our 29 gallon tank numerous times and there’s nothing wrong with it. Last week, one of our yellow balloon mollies died after giving birth the week prior. Then, another yellow balloon Molly died a few hours later by not being able to swim properly and just floating around.
Afterwards, we were left with 2 black balloon mollies (one male, one female) and one female yellow one. The male black molly repeatedly chased the yellow one until eventually the yellow molly died earlier today.
What are we doing wrong???
Robert Brand says
Mollies are notoriously sensitive to anything going wrong in their aquariums. Do you have any live plants (I find they help stabilize the water even more for mollies)? How long do you normally have them for before they die?
Jeremy Armstrong says
Hi, so I’m in an odd situation. I have a 3 gallon hydroponic tank that is recommended for a betta, and had a betta fish in it. The betta was not doing well, and I went to the place where I bought him to ask what I should do. They guy recommended before buying water testing stuff to just see if he was old and bored so to get him some tank mates. I was skeptical since bettas notoriously don’t play well with others, but he was convincing and I’m pretty much an aquarium novice, so he recommended two little mollies so the betta can’t focus on just going after one of them. So I bought two small mollies (one just about 2 cm in length, and the other even smaller). It turns out the betta was just not doing well, so he wasn’t too interested in the mollies, or anything else, and died two days later. So now I have two small mollies in this 3 gallon tank. I found your site which says minimum 10 gallons. Also, the guy said I could feed them betta food, which is freeze-dried blood worms and betta pellets. I’ve put a couple in the tank, and so far they don’t seem too interested. So any recommendations on if I should keep these mollies? They seem alright so far. One of them seems to be very interested in one of the snails in the tank. Also, is feeding them the betta food OK, or should I get the flakes? Thanks for any advice!
Robert Brand says
I really hate when stores employees get it so wrong. First of all, the mollies should be fine with the betta food, but they also need some plant matter in their diet. So maybe supplement with blanched, lightly shelled peas occasionally or small pieces of other vegetables.
As for the size, you’re quickly going to run into problems. Not only do mollies grow large, but they also produce a lot of waste. The water will quickly foul and will probably kill them. It’s pretty safe to keep them in the tank while they’re young, but you want to upgrade their tank as soon as possible.
Marlene says
Where are you located I would like to have a few for my tank
Robert Brand says
Hello Marlene. I’d love to share some with you, but I’m not breeding mollies any longer.
Rebecca Ward says
I have set up a new tank with Mollies, this morning most of them are at the bottom of the tank and not moving much, other than a shimmy of their body (I guess to keep the water moving over their gills) would they be sick or is this normal? I have set the heater for 26C would this be to warm?
Robert Brand says
They definitely sound sick. The first thing I’d do is test the water. Also, how did you add them to the aquarium?
If the water is fine, was there any sign of disease in the tank you got them from? Do they look bloated? Any white strands on them, almost like cotton candy? Are they eating?
Noralene Ballou says
can mollies eat duckweed?
Robert Brand says
For the most part, they usually nibble on it, but don’t put much of dent in duckweed. However, if they’re hungry, they will nearly clear a tank of duckweed.
Lilah says
well please someone HELP!!!!!! My fish is giving birth to baby fish now and i need to know where and what i should do so HELP ME PLEASE!!!!!!!!!!!!!!!!
Robert Brand says
With mollies, there isn’t a lot you need to do. Just make sure to keep the water clean, and if you want a lot of the babies to survive, you should place the fry in a breeding net. Also, if you’re feeding flake food, you should crush it up to make it small enough for them to eat.
Annie says
My orange molly seems to be pregnant. She gets chased constant,y by a big black female and a small orange male who actually used to hang out with her constantly in a good way. The black one used to be super shy but then she had babies. Anyway the orange molly is now swimming in one spot and the fish are actually ignoring her for once. The other orange one will swim up to her but will then swim away. She has been doing this nonstop for a couple of hours. She did have babies less than a week ago, last Saturday night from when I am writing this. But she is still fat and I think she might be pregnant. Does the swimming in one spot and lack of bullying mean anything?
Robert Brand says
It might actually be bloat, which is a pretty serious illness. But first, make sure it’s not a swim bladder issue. Lightly blanch some peas and remove them from their shell, then feeding them to the mollies. Often when a fish becomes bloated like that, peas will often clear it up.
If the peas don’t help and she continues to worsen developing any of the following – scales standing up, white poop, lethargy, lack of appetite, then you need to consider treating for bloat. But it can be very difficult to treat and can spread to other fish in the aquarium. First of all, change the water. Try to get the water quality up immediately. Then consider feeding some antibiotic food to the fish, but as bloat can come from viral and parasitic infections too, the antibiotics may have no effect. To be honest, if it is bloat, the chances are slim that your fish will survive.
But try the peas first and see if it clears up and then go from there.
Christine Johnstone says
i have been using Marine salt 4 Mollies, is there a difference from Aquarium salt ?
Robert Brand says
Marine salt usually contains essential elements, trance elements, calcium, and other beneficial additives. Aquarium salt is normally just unadulterated salt – which means it’s just salt with iodine and anti-caking additives. As long as you’re not using too much marine salt, it should be fine. Just remember it doesn’t evaporate and builds up, so it should only ever be added during water changes.
Roy Storms says
My Dalmatian Molly turned Black?. My Shirt Tatra did also around the back half?. dose the light color cause this?.
Robert Brand says
Was the molly very young when you got it? It’s pretty normal for a molly like that to darken as they age.
Amanda E. says
I’ve been having issues with my mollies eating the fry. I added a lot of coverage plants to help deter them but it’s still not working… how can I yield more babies from my molly fish?
Ashlei H says
I have a 10 gallon tank with 5 mollies. All of them seem to swim at the top of the tank, until i turn the light out and than they go down. Is this normal or do i need to check the water PH?
Robert Brand says
Do they appear to be trying to breath from the top? Also, how often do you change the water?
Hiba Thelhath says
Why do my mollies constantly chase one particular molly?? Like, I have 3 normal and one balloon belly molly. The other three are chasing out the balloon molly. Sometimes they chase out each other also.
Robert Brand says
Do you know if the molly is a female? Most like, they are chasing a female in an attempt to mate with her. Alternatively, it could be normal aggression between males, which is usually nothing to worry about. But if you only have the one female and two males, you should consider adding a few more females.
T says
My molly just had babies about a week or so ago.. she had 5. I put her back in the tank with the other fish. There is a male molly that’s like her and a black molly. They won’t leave her alone. I’ve noticed she’s very large in the belly again.. could she have more babies this soon? I now have her in a breeder tank by herself in case this does happen. I put the breeder tank inside the 10Gal that her first set of fry are growing up in.
Robert Brand says
Does it look swollen or just large? Are the fish scales sticking up at all, almost like a pine cone? It could be pregnancy, or it could be bloat. Generally, the belly shouldn’t swell that quickly. Let me know what you find and we can proceed from there.
Emilia Bieth says
how many molly’s can i keep in a 10 gal tank? I know i have a pregnant molly now and about to burst soon. I think its been at least 35 days so far… she is swollen like crazy. I just learned about balloon molly’s so I am going to check for the spot on the anal fin to make sure she is not a balloon molly. 60 gestation correct?
Robert Brand says
Yes, the gestation is on average around 60 days. Does she have the gravid spot (a black area by the anal fin). You always need to be careful when a fish balloons like you describe, as it could be bloat. But with a molly, it’s most likely pregnancy.