Black Molly Quarantine

Humblefish

Dr. Fish
Preface - Freshwater (FW) black mollies have been used for years in saltwater aquariums for algae control. However, this write-up will focus on their potential for identifying marine fish diseases present in a display tank (DT) and also quarantine tank (QT). The most important detail is to ensure you are using Freshwater black mollies for this purpose. Two reasons:
  1. Evidence of ectoparasites (e.g. ich, velvet, brook) will show as white spots on a fish or translucent for flukes. This makes them easier to see on a black colored fish.
  2. A freshwater black molly will have no acquired immunity to marine diseases, thus making it probable for visible symptoms to show. (In this study, a stable infection of Cryptocaryon irritans was maintained for 2 years using black mollies.)

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Acclimation - A slow acclimation period is best. I prefer to setup a simple 10 gal tank (pic below) and convert them to saltwater over a week. Most (freshwater) diseases the mollies were carrying will be eradicated once they are in full seawater. If you happen to see white stringy poo coming out of any of them, food soak API General Cure or Fenbendazole as outlined here. Mollies are primarily herbivores, prefer low flow and have other requirements explained here: Keeping, Breeding, and Raising Saltwater Mollies

The larger black mollies (Sailfin or Balloon) hold up better than the smaller ones in a saltwater environment.


Testing a Fallow DT - The only reliable way to eliminate a fish disease from a reef tank is to starve it out by going fallow: Fallow periods: Going Fishless

You can test to see if a fallow period has been successful by using 2-3 black mollies before introducing your QTd fish back into the aquarium. I advise a 2 week test period before giving the all-clear. You can house the mollies in an acclimation box or low flow area of your sump; or let them swim freely in your DT (they are easy to catch). If evidence of disease presents itself on any one of the mollies, they all need to be removed, treated and the fallow period restarts. Furthermore, these same mollies may no longer be suitable for testing marine diseases in the future. They are now SW fish who have encountered (and possibly started to build up immunity to) a marine disease.

QT Usage - Certain fish (e.g. anthias, mandarins, wrasses) are notoriously sensitive to medications such as copper and Prazipro. This can make it difficult to chemoprophylactically treat them for Ich, velvet, flukes, etc. Compounding the problem is wrasses, clownfish, dragonets and other species have a thick mucous coat which often hides visible physical evidence (i.e. white dots) of parasites. What to do? Black mollies to the rescue! :D

By quarantining black mollies alongside, this allows you to use them as "canary fish" to detect the presence of disease even if none of the other fish in QT are showing symptoms. This can be done via observation in a medication-free environment. However, I stress the following:
  1. The observation period does not start until mollies are added to the QT. This should happen as soon as (or even just before) fish are added. Because you are having to wait for any parasites to drop off, encyst and then release free swimmers to infect the mollies observation time should be 4-6 weeks.
  2. Be aware that not all SW fish are suitable tank mates for mollies. They are easily bullied or even eaten by large aggressive species (e.g. triggers, groupers, eels). So, the mollies may need to be housed in an acclimation box or by using a tank divider.
  3. Watch the mollies (and all the other fish) for symptoms of disease every single day. So, this is not a reliable method for those with busy schedules, or who will have to leave the QT unobserved due to work/vacation. Watch for visible physical symptoms to manifest (e.g. white dots/splotches), and also behavioral symptoms of disease. Heavy breathing, lack of appetite, scratching, lethargy, head twitching, swimming into the flow of a powerhead are all things which can forewarn you that trouble is on the way. :eek:
  4. Once symptoms of disease have been observed/detected, all fish in the QT must be treated ASAP. This includes the mollies! And again, any mollies who have encountered a SW pathogen should no longer be considered viable for testing marine diseases in the future.
  5. This method is less reliable for detecting flukes, since those often infect the gills and are more difficult to see when they crawl over the scales. (And they would crawl pretty fast over a small molly.) Still, a molly (dead or alive) can be checked for flukes at any time by performing a FW dip. This is going to sound harsh, but better to FW dip a hardy molly than subject a more delicate specimen to the same test.
Concerns - I understand some will have ethical concerns about using mollies as "canary fish", and I am sensitive to that. The more I research & experiment, the more I find there is no perfect solution when it comes to quarantining our prized specimens. However, using FW black mollies to test for SW diseases is an accepted practice by Marine Biologists and public aquarium curators. And I feel the science is solid to extend this practice to also include QT environments, for those hobbyists who prefer to just observe and/or less inclined to use meds as a prophylaxis. At the end of the day, the objective of QT is to introduce disease-free fish into the DT by any means possible.

However, I stress that once you buy FW black mollies you have a moral obligation to care for them the same as any other fish. They are not "throwaway fish" to be discarded after they have served a purpose. Mollies are "reef safe" algae eaters and adapt well to a reef environment. Or they can be housed in a quiet sump area (e.g. refugium) or as semi-permanent QT inhabitants (until a disease pops up.) You also have the option of just converting them back to full freshwater. However, I urge you to care for them yourself, or rehome them to someone with a dedicated FW tank. Sending them back to a LFS leaves open the possibility that another reefer may purchase them for the same reason, and those mollies might fail to test positive for a disease which they have already been exposed to. 😷
 

Jim McNamara

Active member
I did this to a 70 gallon reef early spring. Just one though. It never showed signs of disease. Had velvet in it last year. Is one good enough or should I get several to try in it? Also, is this pretty fool proof? No signs so in go qt’ed fish? That tank was full of a nice lettuce type algae but never saw it eat any.
 

Humblefish

Dr. Fish
I did this to a 70 gallon reef early spring. Just one though. It never showed signs of disease. Had velvet in it last year. Is one good enough or should I get several to try in it? Also, is this pretty fool proof? No signs so in go qt’ed fish? That tank was full of a nice lettuce type algae but never saw it eat any.
I always use 2-3 for good measure, and I've never had this technique fail me.

Are you saying the molly test didn't work for you? Or wanting to know if you are in the clear now since the molly has been disease-free since the spring??
 

Paul B

Well-known member
  1. The observation period does not start until mollies are added to the QT. This should happen as soon as (or even just before) fish are added. Because you are having to wait for any parasites to drop off, encyst and then release free swimmers to infect the mollies observation time should be 4-6 weeks.
  2. Be aware that not all SW fish are suitable tank mates for mollies. They are easily bullied or even eaten by large aggressive species (e.g. triggers, groupers, eels). So, the mollies may need to be housed in an acclimation box or by using a tank divider.
  3. Watch the mollies (and all the other fish) for symptoms of disease every single day. So, this is not a reliable method for those with busy schedules, or who will have to leave the QT unobserved due to work/vacation. Watch for visible physical symptoms to manifest (e.g. white dots/splotches), and also behavioral symptoms of disease. Heavy breathing, lack of appetite, scratching, lethargy, head twitching, swimming into the flow of a powerhead are all things which can forewarn you that trouble is on the way. :eek:
  4. Once symptoms of disease have been observed/detected, all fish in the QT must be treated ASAP. This includes the mollies! And again, any mollies who have encountered a SW pathogen should no longer be considered viable for testing marine diseases in the future.
  5. This method is less reliable for detecting flukes, since those often infect the gills and are more difficult to see when they crawl over the scales. (And they would crawl pretty fast over a small molly.) Still, a molly (dead or alive) can be checked for flukes at any time by performing a FW dip. This is going to sound harsh, but better to FW dip a hardy molly than subject a more delicate specimen to the same test.

I have 5 mollies in my tank and I quarantined and acclimated them similarly yet a little differently.
I carefully opened the bag, stuck my hand in there and from about 4 1/2' away, basically threw them in.

It has been a few weeks, maybe 5 and except for 2 or 3 of them that I think have PTSD, the rest are fine. :p
 

Paul B

Well-known member
I believe the flight through the air basically cares any parasites to death so you are good to go.
I also think they were about 20 cents each. But they seem fine. (y)
 
Late to the party. Sorry guys. But I've had a Molly for quite some time. I put it in my display after running my fallow period. It was a 2 week period before I could add more fish. I just wanted to know it was all clear. I've got a reef tank with most the tank getting decent flow. The Molly adjusted to that and did great. She paired up with my clown for a while until he turned into a she. The clowns turned in her so I put her in my frag tank. She gave birth days later. I have to assume that had to have something to do with the clowns turning in here. They were always together till she got close to birthing. But my plan was to eventually move her into the frag qt system anyway. That way I can test any new coral for ich / velvet before they enter my display. Now I've got a few extras in the frag tank! I ended up with 14 babies that went through the overflow, somehow made it through all the filtration, and ended up in the sump where the clean up any algae. I'm a big fan of them. I just wish the clowns hadn't turned in here. I'll add a large male to my display again.
 

Jessican

New member
I’m going to be upgrading my main tank soon and plan to have tangs. I’ve never had a known outbreak of anything in this tank, but to be safe, I added three mollies yesterday just to make sure the tank is clean prior to upgrading and adding any new fish (which I will be QTing and prophylactically treating).

Just to make sure I’m understanding correctly - if the mollies do not develop any symptoms of disease within two weeks, it’s safe to consider that display clean, correct?

I also have two other tanks that are fallow due to a velvet outbreak - after the 6 week fallow period is over, if mollies in those tanks do not show any signs after two weeks, I can also assume that these two tanks are clean as well, right? I just want to make sure I’m not misreading anything.
 

Humblefish

Dr. Fish
Just to make sure I’m understanding correctly - if the mollies do not develop any symptoms of disease within two weeks, it’s safe to consider that display clean, correct?
Yes

I also have two other tanks that are fallow due to a velvet outbreak - after the 6 week fallow period is over, if mollies in those tanks do not show any signs after two weeks, I can also assume that these two tanks are clean as well, right? I just want to make sure I’m not misreading anything.
Yes

Black mollies have no acquired immunity to saltwater pathogens, which makes them the perfect "canary" fish. And since most saltwater parasites cause excess (white) mucous to form on the fish's scales, it shows up immediately on a black molly.
 

Jessican

New member
Yes



Yes


Black mollies have no acquired immunity to saltwater pathogens, which makes them the perfect "canary" fish. And since most saltwater parasites cause excess (white) mucous to form on the fish's scales, it shows up immediately on a black molly.
Great, thank you! They are black balloon mollies. I just wanted to make sure the two week timeframe was sufficient. They’ve been in the main tank for 24 hours so far and are doing well - here’s hoping that display tests clean.

One follow up question about the fallow tanks - I think I read that you can put them in the tank for two days, then move them to an unmedicated QT to observe for the two weeks, so that if anything shows up, it doesn’t reset the fallow period in the display. Is this accurate?
 

Humblefish

Dr. Fish
One follow up question about the fallow tanks - I think I read that you can put them in the tank for two days, then move them to an unmedicated QT to observe for the two weeks, so that if anything shows up, it doesn’t reset the fallow period in the display. Is this accurate?
No, you want to leave them in the fallow DT for the entire 2 week period. If any of the mollies "hit" with a disease, quickly convert them back to freshwater (to eradicate the disease) and restart your fallow period. Also, it would be best to rehome these mollies to someone with a freshwater aquarium being they are no longer useful "canary" fish since their immune system has now been introduced to a SW disease.
 

Jessican

New member
No, you want to leave them in the fallow DT for the entire 2 week period. If any of the mollies "hit" with a disease, quickly convert them back to freshwater (to eradicate the disease) and restart your fallow period. Also, it would be best to rehome these mollies to someone with a freshwater aquarium being they are no longer useful "canary" fish since their immune system has now been introduced to a SW disease.
Okay, thank you! I was hoping to avoid having to risk restarting the fallow period, but better safe than sorry. :)
 

MattR

Member
No, you want to leave them in the fallow DT for the entire 2 week period. If any of the mollies "hit" with a disease, quickly convert them back to freshwater (to eradicate the disease) and restart your fallow period. Also, it would be best to rehome these mollies to someone with a freshwater aquarium being they are no longer useful "canary" fish since their immune system has now been introduced to a SW disease.
My fallow period will be over soon, what would your thoughts be on putting some live rock, sand, and water from the DT in a qt with the black mollies for two weeks so if a disease does hit I don't necessarily have to do another 76 days? I was thinking if they're clean I could then move them to the DT for another 2 weeks just to be sure
 

Humblefish

Dr. Fish
My fallow period will be over soon, what would your thoughts be on putting some live rock, sand, and water from the DT in a qt with the black mollies for two weeks so if a disease does hit I don't necessarily have to do another 76 days? I was thinking if they're clean I could then move them to the DT for another 2 weeks just to be sure
That strategy will be hit or miss. As you approach the end of your fallow period, any remaining tomonts will be few and far between. Probably inside your largest rock(s) where conditions can be hypoxic.

This explains in more detail: https://www.reef2reef.com/threads/why-a-fallow-period-will-sometimes-fail.536167/
 
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