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Keeping, Breeding, and Raising Saltwater Mollies

Black Molly


Acclimating Mollies to Saltwater

You might be wondering how Mollies can be both saltwater and freshwater. Well, the fact is, they're neither. They originally come from Brackish water, which is a mixture of fresh and salt. Most mollies are breed and raised in Freshwater aquariums, which is why many consider them a freshwater fish. Their natural habitat allows them to be able to live in both freshwater and saltwater. Some argue that they are healthier in Brackish water. However, it is my belief that they have a much healthier and richer environment and therefore much better health in a saltwater aquarium. Saltwater also kills most of the major diseases Mollies can get, which is another benefit.

You might also be wondering what species of Molly to use for this. I would personally suggest the Mollienesia latipinna. The most common types of this species found in pet stores is the Black Molly and Dalmatian Molly. It is easy to find in nearly any fish store, it is hardy, easy to spot in an aquarium with white sand and rock, and cheap. Their fry are also much easier to find in white sand. I have not heard much about other species of Molly being acclimated, so I will not comment on any others. I have however successfully acclimated Balloon Mollies with no issues.

Acclimating a pure freshwater Molly to saltwater can take a lot of time. The amount of time required is argued by many, some say 1-2 hours and some say 2 weeks or more. The average agreed-upon acclimation time is about 6-8 hours. If acclimated correctly, there has been very few reported deaths or signs of stress in this amount of time.

For acclimation, I would suggest a small drip-line setup. Set the drip to very slow, so that it would take about 7 hours to double the amount of freshwater in the acclimation container. Every 30 minutes to an hour, take a small amount of water from the acclimation container. I would say only about 2-5 percent of the water at a time. This will slowly remove the freshwater and increase the salinity in the container. Keep all, or the majority, of lights in the room turned off or very low. Stress is the main risk factor in this acclimation process and bright lights are known to cause extra stress to fish (as well as other animals).

If you happen to have some in stock, a small dose of stress coating couldn't hurt in the acclimation container. If these are new fish from the store, do a Melafix dip before putting them in the acclimation container. Keeping them in Melafix-filled water with no circulation for 6 or more hours is not going to help their stress.

After 6-8 hours have passed of this, your container should have the same salinity as your target saltwater aquarium. A notch or two off isn't much to worry about. Assuming everything has went smoothly, you may now begin putting the mollies into the saltwater aquarium. Turn the aquarium's lights off, and any strong lights in the room off as well. If you have any strong powerheads, it might be beneficial to turn these off too. Remember, a major risk factor is stress, and less light as well as less strength spent fighting powerheads the better. Don't stop the flow of your aquarium though, keep your filters going and enough powerheads to keep a good circulation.

Caring for Saltwater Mollies

I will assume you have done your research and already know how to care for Freshwater Mollies in a normal Freshwater aquarium. If you haven't done your research, you should do it now.

In a saltwater aquarium, there are a few things, such as live rock, that don't usually appear in freshwater ones. Mollies swim in all of the zones of the aquarium, so they need plenty of swim space. When eating, they are near the top. When resting, they generally "sit" above the sand bed. When swimming around and searching for snacks, they swim mostly in the middle zone. The placement of your live rock can be very important.

Mollies definitely need at least a small amount of open sand bed, a major part of the middle zone, and all of the top zone. In my aquarium, I have about 33% of the sand bed showing, with the majority of the rock in the lower middle zone with only a few higher than that. Mollies occasionally go in caves to hide, so it is a good idea to have a few well-placed caves or hangovers for them, but it is not required.

Mollies are generally good temperament and get along with most fish. If you have too many males, they can be territorial and nip at tails, so it's best to only have about one male to three females and only one male per 10-20 gallons. There is no limit to the number of females you could have. They will eat fry, though, as well as eggs. So do not put them in a breeding aquarium or one where your other fish lay eggs or bear fry often.

A molly is a fast fish, so do not keep them with slower fish who may have trouble finding food due to the mollies quick eating. An example of this would be pipefish or seahorses, as they are both very slow and unable to compete for food with fast fish. Do not keep mollies with aggressive fish, as they cannot fend for themselves very well and do better in community or species-only aquariums.

Feeding Saltwater Mollies

Feeding a saltwater molly is mostly like feeding a freshwater molly. The main difference is that some of the things you would feed a freshwater aquarium may be unhealthy for saltwater fish. Your feeding options can greatly depend on what else is living in your aquarium, so try to find a food that both your saltwater fish and your mollies enjoy. I personally feed my mollies Formula One Marine Pellet (Small), along with Algie Wafers which I feed my snails. They will also eat brine shrimp, mysis, and most small live or frozen foods.

Most mollies will also eat some algaes and clean the walls of your tank, though they rarely eat enough to actually clean it. The majority of mollies from a pet store will not be very good at eating Copepods or other natural saltwater foods, but they should eventually begin to snack on them. Do not rely on copepods or other critters in your tank as a primary food source for them.

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Whatever you do, make sure that the food you are feeding them is small. Depending on the species, most mollies have tiny mouths and will spit anything large out. Small pellet foods usually work fine. When feeding brine shrimp, make sure that they are young or baby shrimp. If your mollies are not eating, and no food is working, try soaking it in liquid garlic, which can be found in most fish stores.

Breeding Saltwater Mollies

You can tell a male from a female very easily. Look at the Anal fin (the fin on the bottom, in the back near the tail), and look at it's shape. A female will have a rounded, large fin. A male will have a skinny pointed fin. There are tons of guides and pictures to make this even easier online, and since I am assuming you have already done your research, I will not go any further into this.

The number of fry can be over a hundred, depending on species. The number that survive is much different however, depending on how you handle the fry being born. The main difference between breeding in freshwater and breeding in saltwater is finding and catching the fry when they are born.

You can always separate the pregnant female in another saltwater aquarium designed as a nursery, but if this is too much trouble the female can easily give birth in the main aquarium. The problem, however, is separating the fry once hatched. Since saltwater aquariums usually have lots of space, rock, plants, corals, and so on, these can be hard to find. Some fry will be lucky and be able to hide themselves in the thousands of places a fry could fit. Some however will not be so lucky. The mollies will eat their fry as snacks without hesitation, as will most other fish. The filter can kill many of them depending on your filter setup. Powerheads are another enemy, among many other problems and equipment that can kill fry. What I usually do is have a breeding net inside the aquarium, and a long net for catching fry. I catch the fry whenever some come out of their hiding places and throw them in the breeding net quickly, and repeat. Of course, it's a lot easier to separate a pregnant female if you know she is about to bear more fry.

As a supplement to this, I would suggest reading a few more freshwater molly breeding guides online if you plan on breeding often.

Raising Saltwater Molly Fry

Mollies are Livebearers, which means they breed and have live fry, like cats have live kittens, rather than laying eggs. The fry are fairly large at first and will begin swimming almost immediately. The first hour or two they will have a yolk sack on their belly, and right after that is gone they will need to begin eating real food.

Molly fry are best fed live baby brine shrimp (within the first 12 hours of the brine hatching), or very fine flake flood. If you have trouble feeding them the brine shrimp within 12 hours of them hatching, due to work schedules or otherwise, you can use baby brine shrimp born within the last 24 hours and feed them a supplement with a lot of fatty acid.

If you want as many to survive as possible, I highly suggest setting up a small nursery aquarium using water from the main aquarium. You should also setup a brine shrimp hatchery, as they are much healthier than flake food. Equipment needing to make a nursery:

  • 10 gallon aquarium
  • Sponge Filter (Not a power filter)
  • Heater (set to temperature of main aquarium heater)
  • Gravel Cleaner (This is a tube where you can siphon water out and easily clean the bottom of the aquarium of old flakes and dead shrimp)

Do not use gravel in a nursery tank, as it will only make it more difficult to keep clean and watch your fry. With a bare bottom, you can clean all old food out without any problems and keep track of how many fry have died. Try to use water from your main aquarium, or at least some of it. Make sure that your nursery tank has the same test results as your main aquarium and try to keep them at the same temperature. This all makes it much easier to transfer the fry to the main aquarium when they're older with the least amount of stress.

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Mars Liu on March 20, 2018:

I raised over a hundred black mollies in my aquarium tank, all of them are given by one female molly. My mom loves them so much and considers it a sign of prosperity based on our culture context. They are so lovely and bearable. Thanks for the sharing that gives me more confidence of raising them well.

Doe on June 25, 2013:

I am acclimating a couple black mollies to salt as I type. This is not new to me and hoping for same good results. My first procedure went well several years back with Dalmation mollies. The fry born in salt were larger than those in fresh. The females reached a larger size also when mature, My reason was for available live food in my salt water tank.

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