Aquarium Fish

Molly Fish Care

The Molly is a tropical fish that prefers some salt in their water. A teaspoon of aquarium salt per 5 gallons of water will go a long way in helping them. You may also see them in saltwater tanks from time to time. There is a local reef store here that keeps black mollies in a regular saltwater tank with similar sized species. It is a very attractive tropical fish that comes in many different colors such as orange, green and black. Some of the more popular varieties include the sailfin, balloon and the dalmation.

For Molly Keepers

This is a livebearing tropical fish that can be fairly easy to breed. For many aquarists the biggest problem is not getting them to breed but stopping them from breeding. If left in a tank with other adult fish, the babies will get eaten.

They will eat flakes, frozen, freeze dried and definitely live foods.

Regarding Balloon Mollies; the balloon trait is obtained by selectively breeding fish with scoliosis (bent spine). Balloon mollies often have a reduced lifespan due to three factors: the inefficiency of the misshapen morphology causing wear and tear while swimming, the compact position of its internal organs in comparison to a non-balloon variety, and oft-seen difficulties giving birth.

To salt or not to salt?
Sailfin and black mollies can tolerate a little bit of salt (mexican mollies require it), up to about 1 table spoon of salt per gallon. It has been argued, however, that salt actually irritates their skin. I myself only use salt in cases of ich. If you do use salt, please use aquarium salt and not kitchen salt (has natrium in it) or marine salt (has minerals in it).


Black Molly

Giving Birth Video

Care Sheet

Scientific Name : Poecilia sphenops, P. velifera, P. latipinna

There are 3 different species of mollies, which have been re-classified, ungrouped and re-grouped several times. Today's consensus is as follows:

Peocilia velifera (also called P. mexicana) = Yucatan molly. Sometimes erroneously referred to as sailfin.

  • Size: Larger than P. latipina (about 8cm/6in for big specimens).
  • Dorsal fin: Males' dorsal fin is high. It has more rays (about 18) than the latipinna. Also, upper edge of dorsal longer than lower. Dorsal fin markings are slight, small spots.
  • Salt: really need brackish water to thrive.
  • Other requirements: They need direct sunlight, and more gallons per fish than the latipinna.
P. latipinna ('true' sailfin).
  • Size: Smaller than velifera (about 6cm/3in for big ones) and more slender
  • Salt: Tolerate some salinity but do not require it.
  • Dorsal fin: The males' dorsal fin is high. has less rays (about 15). Also, upper edge shorter than lower edge. Their dorsal fin is edged in a yellow line and they have dark and square markings on the dorsal fin.
P. sphenops (short-fin, e.g. black molly).
  • Size: Smaller yet than the latipinna (about 6cm/3in for big males; 5in for big females) and more slender
  • Salt: Tolerate some salinity but do not necessarily require it.
  • Dorsal fin: Their dorsal fin is a lot less high than either sailfin type.

Some morphological varieties have been bred into the three species: you can now find balloon (pot-belly) and lyretail varieties, for example, and a whole sort of color assortments.

Common Names : Lots of different types are available: Black, Lyretail, Sailfin, Liberty, Mollie, Pointed Mouth, Short Finned, Mexican, Golden, Piebald, Ghost Pearl, Gold Dust, Red Sunset, Dalmation, Ballon, etc.

Care Level : Easy and a very good for beginners if keeping a single sex. Keeping both sexes could cause problems since this fish is such a prolific breeder.

Size : 2 to 4 inches (5 - 10 cm) depending on the species

pH : 7.5 - 8.5

Temperature : 70°F - 82°F (21°C - 28°C)

Water Hardness : 10° to 25° dH

Origin / Habitat : Central America

Life Span : 3 - 5 years

Temperament / Behavior : Peaceful

Breeding : These are livebearers so it is fairly easy. Adding a little aquarium salt will help. Do you have a pregnant molly? Read the breeding guppies article for more information. That article talks about guppies and swordtails, but the process is very similar for the babies.

If you want to try and raise the fry think about getting a breeding box or breeder net like these:

Frequently asked questions and answers on breeding them:
How can I tell if it's a male or a female?
The male has a pointy-shaped anal fin (gonopodium), whereas the female has a 'normal' triangular set of anal fins. For sailfins, the males also have a high dorsal fin.

How do I know they're mating?
The male will constantly chase the female and point his gonopodium towards her belly in the chase.

How long is the pregnancy?
Normally speaking, the gestation period is abour 4 weeks after mating. They can get pregnant immediately after giving birth, so it's not uncommon to have your females nearly PERMANENTLY pregnant, and giving birth every 4 weeks or so.

Females can hold sperm without letting it develop into fry for a very long time (weeks and weeks on end). They'll do that if they feel the conditions are not right for their young to develop. This is causing the oft-seen phenomenon of females arriving pregnant form the shop, prompting many people to bewonder the miracle of immaculate conception, or extreme cross-species breeding with, say, blue whale tank mates.

What's a livebearer?
They are livebearers, which means that the fry is born free-swimming. They are ovoviviparous, though the young does have an egg stage inside the mother, unlike mammals, which are viviparous (no egg stage at all: the baby IS the egg).

How many fry will she have?
A young female's first ever batch can be as little as a dozen fry. As she gets pregnant again (and again, and again and again...), she's likely to give birth to increasingly large batches. Some people report prolific mothers regularly give birth to 80 or so fry per batch. They may give birth in 2 or more phases, releasing the second half a week or so after the first batch was dropped.

How do I know she's pregnant?
A female about to give birth will look almost boxy in shape, distended that she is with all the fry inside her. Another tell-tale sign that she's about to give birth is that she may lack appetite a day or two before dropping her fry. She'll also likely isolate herself form the others, and lay in a quiet spot on the substrate. This behaviour often prompts panicked owners to diagnose a disease, but it's common in pregnant livebearers, and she'll soon recover her spirirts. If your fish is relatively transparent in color, you may distinguish what is called the gravid spot on her abdomen. This looks like a darker spot, and is the mass of fry that you can see through the fish. The closer she is to dropping, the closer the spot will be to her cloaca.

Why does my fry disappear?
They (and other tankmates) can eat their young. The young also commonly get trapped under gravel. If you want to keep your fry alive, you'll need to either provide plenty of cover for them (a floating plant, mini pots/jars on the substrate, stacked flat marbles or a densely planted area should ensure that some of your fry makes it to adulthood) or to isolate the female prior to her giving birth. I personally never isolate my pregnant females, as it stresses them out. Simply speaking, the fry cease to be in danger when they are too big to fit in the tank mates' mouth.

When do I know if the fry are male or female?
You can sex the young from about 3 months old. Before that, the immature fry will all look like females. Do separate them from their parents before they reach maturity to avoid inbreeding.

Interbreeding between species
All three molly species can interbreed. Other livebearers can also breed with mollies. The following interbreeding combinations have been reported: guppy-molly, and swordtail-platys. But beware, the resulting fry are mostly sterile, deformed runts, and you will not be able to give them away to a shop.

Male/female ratio
If you don't want fry all the time, you'll need to separate the males from the females. Same-gender tanks should really have at least 3 together to avoid the alpha fish victimising the subservient fish. Mixed-gender tanks should keep at least 1 male per two, or even better, three, females. You'll soon notice that the male's insatiable appetite would end up exhausting a lone female.

Aquarium Size : 20 gallon minium, prefer tall aquariums

Tank Mates : Not many - some feel they should only be kept with others of the same species.

Fish Disease : Freshwater Fish Disease - Diagnose, Symptoms and Treatment

They can show the following disease symptoms:
Shimmy: get shimmy block or molly bright medication to catch at onset. Shimmy is sign of early development of one of several possible diseases.

Torn fins: either result of a fight or finrot. I would isolate the fish and treat with disinfectant. If it is finrot, you will need to determine whether it bacterial or fungal before treating.

Flashing/scratching: water quality problem (nitrate/nitrite/ammonia) likeliest. External skin parasites also likely.

Lethargy: commonest cause is just pregnancy.

Gasping for air on the surface: temperature could be too high. oxygenation could be too low. could be nitrate/nitrite/ammonia poisoning.

Reddened/purple gills: sign of nitrites/nitrates/ammonia poisoning.

Dull white film on skin: could be oodinium (turn the tank light off and shine a torch on the fish. If the white patch glows back, it's oodinium). Could be a fungal infection (furry-looking white patch, like mold).

Slanted swimming, swimming upright or on the side: possibly a swim bladder problem, or a spine problem. Spine problems can be caused by a vitamin defficiency or by TB.

Pop eye: Symptom of many possible diseases, including the dreaded fish TB. Could also be mechanical damage from fight or knocking against ornament. Pop eye can also be caused by water pollution with plastic or metal, or by ammonia/nitrite/nitrate. In rare cases, pop eye is caused by oxygen oversaturation (gas bubble disease).

Dropsy: (means fish's midsection is extremely swollen, and scales stand upright in worst cases). Symptom of many possible diseases, including fish TB.

Sunken belly: Symptom of many possible diseases, including fish TB. Sometimes the fish has trouble eating from a wound around the mouth area.

Grain-like white spots: Ich.

Constipation: Poo constantly stringing out of fish, or fish's belly really distended.

Stringy excrement: internal parasites.

Diet / Foods : Give them a varied diet consisting primarily of flake foods but supplement with live and freeze dried foods occasionaly. Some feeding tips:

  • Slow-sinking protein and vegetable pellets, served on the surface so they get to chase stuff
  • A variety of vitamin packed flake food promoting growth, color and immune system
  • Fast-sinking protein and vegetable pellets so they have to browse for their food

How Much To Feed Them?
A common rule of thumb is that a fish' stomach is the same size is one of its eyes, so try to stick to one stomach's worth of food per fish per feeding. Feed in slow batches, giving a small portion and waiting until they've eaten it before giving more. Fasting them one day a week is a good idea too.

Tank Region : All over the tank.

Gender : Males are more slender, females more round. Males also have a modified anal fin.

References :


From: Sharon via email
How often do they breed and can you stop them if you want to?
Assuming that you have pairs, they will give birth every 30 days if the tank conditions are right. One sure way to stop them is to remove the males or females and only keep one sex in your tank. Also, keep in mind that mollies, like some other livebearers (i.e. the Guppy, etc.), may remain fertile for about 3 months after getting pregnant and separating them from the males.

From: Albret
I moved my female today to a breeding tank, I think she might have been too stressed and aborted the pregnancy. How can I tell if she did?
Moving too soon to the drop may cause your livebearer to abort the process because of the stress involved. Leave the female where she is and if she does not have any babies in the next week or so you can assume that she aborted the pregnancy. Try to keep them in the same water. Moving to a different tank with different water parameters (temperature, pH, etc.) will cause stress. A Breeder Net or Breeder Box or floating plants like Breeding Grass will allow the babies to hide from the larger fish in the tank.

From: Chris
Mine had about 39 babies and as they grew I couldn't tell the sex of them. I knew the females where more round but does the male have a larger top fin?
You should also be able to tell the difference by looking at the anal fin. It is usually much smaller and more elongated on males.

From: Lisa
On average how many eggs do females lay in one pregancy?
They are livebearers which means that they don't lay eggs. The fish are born swimming. The number of fry depends on the size, age and health of the fish. Generally speaking, they can release anywhere from 2 - 60 babies or more.

From: Sophie W.
How long do they live for?
If kept in good water conditions they generally have a lifespan of 3 - 5 years or more.

From: Haley
How long does the pregnancy last until the babies are born?
The gestation period for this livebearer usually takes about 4 weeks, sometimes slightly longer.

From: Nita
My fish had babies and we put them in a separate tank with the mother and she ate her babies. Is this normal behaviour of females?
Unfortunately, it is common for them to eat their young. Next time just place the babies in the separate tank or get a breeding net for the fry.

From: Leah
I've been breeding livebearers since I was about 12. I've tried breeding betta fish, but the babies are so small and fragile that they always die. I took a long break from livebearers and had some tetras and angelfish. I had a Dalmation Molly that had 14 babies and only one made it to this day. The mom and dad got eaten and I moved the baby one to its own tank immediately. I just bought him an all black girl and she just had 9 babies two days ago! Black babies are the absolute cutest! The 2 adults never picked on them but I moved the parents to a larger tank and bought 2 gold dust mollies and a male swordtail. Breeding this fish is the coolest thing in the world. They are so adorable and is a hobby of mine.

From: L. Fish
Yesterday we bought a white, black and two spotted ones. We woke up this morning and our white molly was dead and now there are about 15 to 20 babies! We had no idea this was going to happen it was a shock to say the least. The others haven't been interested in eating the babies, but we will see.
Most likely they will get eaten by the other fish in the tank. They are similar to other livebearers in that they are prolific breeders. If you have mixed sexes in the same tank, your water parameters are decent and they are being fed adequately, you'll soon have babies.

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