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How To Tell If A Molly Fish Is Dying? Look For These Signs!

How To Tell If A Molly Fish Is Dying? Look For These Signs!

Credit: Pmalkowski (Creative Commons license)

Mollies are incredibly hardy. But they’re not invincible. They live for around 2-5 years, depending on the care they receive. So, when the time comes, how to tell if a molly fish is dying? If you spot the signs quickly, would you be able to save the 


Let’s find out! 

How To Tell If A Molly Fish Is Dying? 

A molly fish dying of sickness or old age will display numerous signs that give away their health status. They may display all or the combination of the following symptoms:

  • Listlessness 
  • Lack of appetite 
  • Erratic swimming patterns 
  • Shimmying 
  • Loss of control and buoyancy 
  • Swimming near the water surface for air
  • Clamped fins 
  • Scratching themselves against 
  • Labored breathing 
  • Swollen gills 
  • Red spots on the body 
  • Bloating 
  • White specks on the body 
  • Protruding eyes 
  • Ulcers around the anus
  • Staying at the bottom
  • Scales sticking out 

Before discussing these pointers in detail, knowing what sets sick fish apart from healthy fish is essential. Below, I have listed some telltale signs of a healthy fish. 

Signs Of A Healthy Molly Fish

The following are the typical characteristics displayed by healthy and happy fish:

  • Active swimming 
  • Rich body coloration 
  • Good appetite 
  • Social behavior 
  • Bright red gills
  • Fins held erect 
  • Alertness 
  • Well-filled body contours 
  • Bright and clear eyes 
  • Gills falling and rising rhythmically
  • Clean vent without stringy feces 

Now that you’re well-versed in distinguishing between a healthy and a dying molly, let’s have a detailed look at some signs that tell the molly’s days are numbered. 

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How To Tell If A Molly Fish Is Dying?

Credit: KauaiGuy808 (Creative Commons license)

Lack Of Appetite 

A molly feeling unwell and is about to die will lose its appetite. The fish will show no interest in eating anymore and will not swim to the surface even when you’re offering its favorite food. 

An average freshwater fish can go without food for 3 days to 1 week. However, the fish’s body will start reacting negatively after just 1 to 2 days of starving. 


Listlessness is yet another obvious sign of a dying molly fish. When the fish’s hour has come, it will neither have the energy nor the motivation to swim around and remain active. 

When healthy and happy, mollies are active and social. They love to school together. 

But a sick fish will naturally lose interest in socializing. It will appear distant and aloof. It will also hide around a lot and stay at the bottom. 

It should definitely be a concern if your molly displays this behavior, coupled with some other signs mentioned above. 

Has Bacterial Infections 

Bacterial infections can be downright fatal if not treated on time. The bacteria that are bugging your molly can either be gram-positive or gram-negative. We strongly recommend seeking professional help to what type of bacteria is causing the problem. 

Below, I will list some most common symptoms of different bacterial infections. 

Type Of Bacterial Infection

Popeye (Exophthalmia)
Cloudy, protruding eyes 
Formations of bubbles over eye region 
Fluid discharge from the eye
Tail/Fin Rot 
Reddish spots on the fins 
Fins falling apart from rotting
Frayed fins 
White dots on fins 
Bloated belly 
Raised scales 
Ulcers along the lateral line 
Curved spine 
Bulging eyes and pale gills 

Bloody red streaks on fins and body 
Clamped fins 
Gasping for air 
Open sores 
Raised scales 
Tail and fin rot 
Gray lesions 
Skin ulcers

Has Parasitic Infections 

Parasites are ubiquitous in all aquariums. While healthy fish are immune against them, stressed fish with compromised immunity fall victim to these opportunistic organisms. 

Below is the list of some common parasitic infections that plague our fish alongside their symptoms. 

Type Of Parasitic Infection

Velvet Disease
Faded colors 
Rubbing body against decors 
Labored breathing 
Rusty colored film on skin
Peeled skin in advance stage
White dots across body
Clamped fins 
Frequent scraping 
Loss of appetite 
Abnormal hiding behavior 
Body Slime Infection
Tattered fins 
White film on the body
Cloudy eyes
Open sores and ulcers 
Swollen gills
Steel gray coloration in affected area
Copious mucus production

Has Fungal Infections 

The fungus is naturally and perpetually present in any aquarium, like bacteria and parasites. They’re pretty much harmless when the fish is healthy. 

However, when the fish is injured or stressed, the protective mucous layer on its body becomes damaged. And that’s when they become susceptible to fungus. 

Here’s a list of some common fungal diseases and their symptoms in fish. 

Type of Fungal Infection
Cotton Wool Disease
Brownish-yellow or whitish gray cotton-like growth on body 
Frequent scraping 
Redness around infected area 
Fungus becomes green/brown in advanced stage
Fish becomes darker 
Erratic and abnormal swimming 
Yellow to green round granulomas in visceral organs like kidney and liver 
Increased hiding behavior 
Bulging eyes 
Small, tactile nodules on skin 
Weight loss 
Erratic swimming

Why Do My Molly Fish Keep Dying?

Although mollies are hardy for the most part, just like any other fish, they too have an Achilles heel. The most common reasons behind mollies dying are disease, wrong environment, uncycled aquarium, overfeeding, travel fatigue, and shocks. 

Wrong Water Parameters 

Wrong water parameters are the silent yet number one reason behind the untimely death of molly fish. 

The spike in harmful compounds like ammonia and nitrite will cause the fish to suffocate and die a slow, painful death. 

For example, if there’s a higher concentration of ammonia in the tank than what’s acceptable, the fish will not be able to extract energy from the food it consumes efficiently. 

Even the slightest exposure to ammonia can affect the fish’s gills and skin tissue. 

Next, it’s only a matter of time before your molly becomes lethargic, falls into a coma, and dies. 

Likewise, the wrong water temperature can deprive the fish of oxygen, compromise its immunity, cause lethargy, and make it susceptible to secondary diseases.

If your fish stays at the bottom a lot, it could mean that the water’s too hot. That’s because colder water that moves to the bottom is relatively more oxygenated than water at the surface. 

Likewise, if the water’s too cold, it will make your molly sluggish and lethargic. 

You Didn’t Cycle The Aquarium 

Adding fish to a tank yet not fully cycled simply means you’re throwing them under the bus. If you’ve added a school of mollies to a newly set up tank and the fish drop like flies one by one, it means the tank has not completed its nitrogen cycle.

Ensuring the tank’s fully cycled is vital to establish a healthy and thriving colony of bacteria that will break the toxins like ammonia and nitrites into less harmful compounds like nitrate. 

Fish aren’t the only organisms living inside your tank. In fact, fish have a symbiotic relationship with microscopic organisms that reside in your tank. 

Without the fish and the waste they produce, the bacteria colony dies. And without the bacteria, water becomes quickly inhospitable for the fish. 

Completing a nitrogen cycle takes several weeks. The process is lengthy, but you shouldn’t lose patience. Otherwise, you’ll end up losing your mollies. 

In brief, a nitrogen cycle has the following steps:

  • Start by adding dechlorinated and treated tap water to the tank 
  • Add flake food into the water as if you’re feeding fish every day 
  • Monitor the ammonia levels 
  • Continue adding fish food into the water 
  • Once the ammonia levels are high, start monitoring nitrite levels too 
  • Ammonia levels will now drop as ammonia-eating bacteria develop, but nitrite levels will increase 
  • Ammonia and nitrite levels will drop to nil, and nitrate will start appearing as nitrite-eating bacteria develop 
  • The nitrogen cycle is completed when ammonia and nitrite are at 0 ppm, and nitrate is below 20 ppm

Your Mollies Are Stressed 

We often think of fish as mindless creatures without much intelligence or emotions. But that’s the farthest from the truth. 

Mollies, like most fish, are highly capable of feeling an array of emotions and are as sensitive as they come. That’s why stress is among the most common causes behind your mollies’ life getting cut short. 

Let me explain how stress kills fish. 

Stress causes significant chemical changes in the protective mucus layer that shields the body. As a result, the effectiveness of the chemical barrier is decreased, and the fish becomes susceptible to opportunistic organisms, like ich, waiting to invade. 

Stress also upsets the normal electrolyte (chloride, potassium, and sodium) balance of the fish’s body, leading to excessive water uptake. 

And lastly, stress weakens a fish’s immunity. And letting the guard down means the fish is now prone to a plethora of secondary health conditions. 

Here are a few signs of stress in mollies:

Glass surfing 

Your molly repeatedly and frantically swims up and down the sides of the tank. This could be because the tank’s too small or crowded, water conditions are wrong, or your fish is sick.

Excessive hiding behavior 

A stressed molly will not socialize. Instead, it will appear irritable and aloof. The fish will resort to hiding among the plants, inside the caves, or behind rocks. 

Weight loss 

A stressed molly will have a lowered appetite, eventually resulting in weight loss. The fish will show no interest in eating even when you offer one of its favorite foods. 


Your molly may be stressed because it’s down with a sickness. Stress often leads to illness and vice versa. I have covered the different diseases and their signs in the tables above. 

Wrong Feeding Style 

Overfeeding is among the most persistent problems in a fish tank – especially smaller ones. 

To put it simply, whatever goes inside your fish must come out. So, the more you feed your mollies, the more waste they produce. 

The more waste they produce, the more quickly the tank will get dirty. 

The plants and the good bacteria colonies will help, but they too have their limits. 

Give your fish small but frequent meals. This will prevent overeating and keep the water quality pristine for a longer duration. 

If you overfeed your fish, this won’t just lead to obesity but also other potential conditions arising from polluted water. 

You need to zero in on quality flake food or several and alternate them. 

Mollies love eating special live food but don’t go overboard with them. Only offer special foods sparingly. 

Some hobbyists also swear by fasting the fish once every week. 

And underfeeding can be equally dangerous as overfeeding, if not more. Diets scarce in protein, essential fatty acids, amino acids, minerals, and vitamins will lead to gross malnutrition. 

Travel Fatigue 

Credit: Neil R (Creative Commons license)

Aquarium fish have to make journeys of hundreds of miles in a plastic pouch. If the ride’s bumpy, the fish will become extremely tired and will die as soon as it gets to your home. 

We recommend buying fish from a local breeder as much as possible. This will prevent the fish from making completely unnecessary journeys. 

Travel fatigue, combined with an abrupt change in environment, can downright kill your mollies. 

Therefore, we suggest that you get your mollies or any other fish from a credible, local seller so you can save the fish from unsolicited travel fatigue. 

And don’t transfer the fish into its new home directly. They don’t react well to a drastic change in the environment. It can very well shock the fish and cause its demise. 

Even the hardiest fish will succumb. 

You can use the drip acclimatization or the floating bag method to acclimatize the fish. 

Here’s an informative video on gradually adding new fish to an aquarium. 

You Made A Terrible Mistake 

I own 4 fish tanks altogether. And I’m pretty confident about my fishkeeping skills now. However, things weren’t always like this before. 

For instance, I’m guilty of keeping fish in rounded tanks for a reasonable time. 

I’d made pretty dumb mistakes when I first started out. 

During one holiday season, I set up an automatic food dispenser for the tank in my office. Smart! I also performed water changes and cleaned everything before we left. Smart again! 

However, it turns out that I completely forgot to turn on the power to the tank back after I was done cleaning. 

My fish had to live in dark, cold, and dirty water for a week. Thank heavens, at least they were fed! 

Luckily, they all survived the adversity – but a few did get really sick! 

What I’m trying to say is that we all make dumb mistakes at some point. And sometimes, it costs our dear pet’s life – it’s heartbreaking. 

If that happens to you, go easy on yourself. We’re just humans, after all. 

Poor Genetics 

Some things, like poor genetic buildup, are entirely out of your hands. There’s nothing you can do to save your molly if it has congenital issues that doomed it from the birth/ 

Unfortunately, large pet stores aren’t exactly known to be the most reliable source for high-quality fish with credible genetic profiles. 

If you have bought mollies from a particular seller many times and each has died, and you’ve checked everything else on the list, and you don’t see any issue, it’s time to get your mollies from a different store. 

When buying fish, don’t go for the cheapest option available. Don’t pinch pennies in this department. 

So, these are just a couple of reasons why mollies die an untimely death. A few probable reasons I didn’t explain above are incompatible tankmates (bullies) and wrong tank size (too small).

Now, let’s look at how to save a dying molly fish. 

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How To Save A Dying Molly Fish? 

You should first transfer the fish to the hospital tank so whatever disease it has contracted doesn’t transmit to other fish. In the new tank, observe its symptoms, maintain the correct water parameters, and most importantly, consult the vet before you use any medication. 

Observe The Fish’s Symptoms 

If you think your molly fish is sick, you should first transfer the fish to the quarantine tank. You need to do so to prevent the disease from transmitting to other fish in the tank. 

For instance, parasitic infections like ich are highly contagious and can transfer from one fish to another without the need for the host. 

Once the sick molly is settled in the new tank, you should closely inspect its symptoms. 

If your fish has respiratory complications, it will show signs like laying at the bottom, gasping for the air, and labored breathing. 

In case of a parasitic infection, the fish will develop blotches and spots across the entire body or a few selective spots. Some other symptoms that will accompany are lack of appetite, reddened gills, and a shriveled look. 

If your molly is suffering from swim bladder disease, it will swim in erratic patterns like floating at the top, sinking to the base, or swimming upside down. Basically, the fish will lose buoyancy. 

As you can see, each condition comes with a unique and particular set of symptoms. To properly treat the fish and save its life, first, you need to diagnose it correctly. 

Practice Good Tank Management

If you are diligent with upkeep, most tanks don’t require that much work to run correctly. 30 to 60 minutes every week is all you need to maintain a tank. 

Here’s a short overview of things you should do daily, weekly/biweekly, and monthly to ensure the tank runs safely. 

Daily To-Do List

  • Check the filters 
  • Check the temperature and heater 
  • Do a headcount and observe the fish
  • Remove leftover food 
  • Top off the water level 
  • Note any concerns in a logbook 

Weekly/Biweekly To-Do List

  • Wipe down the tank’s surface – both inside and outside 
  • Remove debris from plants and decors 
  • Scrape the inside glass 
  • Siphon the gravel 
  • Perform a partial water change 

Monthly To-Do List 

  • Perform water tests for ammonia, nitrite, nitrate, and pH 
  • Prune plants as required 
  • Perform the tasks mentioned in the weekly/biweekly list 
  • Change the filter media

Book An Appointment With The Vet

Sometimes, changing the water, cleaning the tank, and feeding a healthy diet are all that you need to revive a dying molly fish. Other times, you need to seek medical help. 

Fish can suffer from various clinical diseases that can only be treated by professionals. 

Therefore, it’s crucial to observe the symptoms precisely so you can help the vet make the correct diagnosis. 

If the fish shows signs of respiratory illness, the medics will first offer plenty of oxygenation and dechlorinated water on arrival. 

If the fish has to go through surgery, you will be asked to bring sufficient original tank water. 

You will also be asked questions like what species are kept, what fish are down with disease (species, age, and size), if a new introduction to the tank was recently made, the status of filtration, and so on. 

Even if you think your molly’s condition is treatable at home, you should consult the vet before using any sorts of antibiotics or treatments. 

Frequently Asked Questions 

Credit: Dennis Amith (Creative Commons license)

Do Molly Fish Play Dead?

No, as bright as mollies are, they don’t play dead to make a fool out of you. If your molly is acting weirdly, such as lying motionlessly at the bottom and swimming upside down or erratically, it means there’s something wrong with the fish. 

Your molly is either ill, starving, suffocating, or the tank has become unlivable. From what I read on forums, people reported that their mollie died soon after supposedly playing dead. 

So, if you find your fish acting abnormally, you need to quickly intervene and keep on experimenting until you find out what’s causing it stress.

Molly Fish Shimmies – What Does It Mean?

Shimmying is a symptom often seen in livebearers like mollies and guppies characterized by the fish rocking its body violently from side to side, almost in a snake-like slithering fashion. 

The 3 most common reasons behind shimmies are:

  • Cold temperature forcing the fish to ‘shiver’ to generate heat
  • Acidic water (low pH) is burning the fish’s skin 
  • Low mineral content in the water is shutting down the fish’s organs

If you find your molly shimmying, raise the water temperature slightly between 76-80 degrees Fahrenheit. Likewise, increase the pH levels to 7.0-8.0. 

And lastly, if you suspect the water’s too soft for molly, reinforce it with mineral supplements like Seachem Equilibrium, Wonder Shell, and crushed coral. 

How Long Do Molly Fish Live?

Mollies don’t really lead a long life. In captivity, they can live for anywhere between 2-5 years. That being said, their lifespan depends upon the environment they’re brought up in and the food they’re fed. 

Molly Fish White Anus – What Is It?

White ‘substance’ on a molly’s anus could either be a fry that she’s giving birth to or a fungus. If it’s a fungus, you need to use anti-fungal treatments like methylene blue. 

However, we strongly recommend discussing this with your vet before starting any treatment. 

How To Tell If A Molly Fish Is Pregnant? 

The following are some of the most apparent signs of a pregnant molly fish:

  • Swollen and rounded appearance 
  • Aggressive and aloof behavior 
  • Prominent and visible gravid spot 
  • Increased appetite 
  • Strong bulge below the gills 

Why Do My Male Mollies Keep Dying?

Your male mollies are dying due to the same reasons most livebearers die untimely. A polluted environment; high levels of stress; bacterial, fungal, or parasitic infection, wrong diet; and mean tankmates could be why. 

Final Words: How To Tell If A Molly Fish Is Dying? 

I didn’t expect the article to be this long, but here we are. I hope you found the answers you were looking for. 

In a nutshell, the most common signs of a dying molly fish are lack of appetite, erratic swimming style, lethargy, panting, visible signs of injury or illness in the body like red or white spots, flashing, clamping fins, loss of balance, and shimmying. 

On the flip side, a healthy fish demonstrates the following signs: active swimming, good appetite, rich coloration, alertness, bright eyes, and clean vents without stringy feces. 

Recommended Readings!

How Long Are Molly Fish Pregnant For? Twice As Long As Guppies!

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