mollie fish

How To Tell If A Molly Fish Is Dying

Mollies are hardy little fish, but they can succumb to parasites and diseases, just like any other fish. Molly fish often die if you do not manage the quality of the water in their aquarium properly.

If you are worried about your mollies and want to know if they are dying or not, keep reading! This article discusses how to tell if a molly fish is dying, the most common causes of death in mollies, and how you can save a molly fish that is dying. 

Tell If A Molly Fish Is Dying

How To Tell If A Molly Fish Is Dying – Key Signs To Look For

To tell if a molly fish is dying, you must look at its physical appearance as well as its behavior. Your molly fish may not always present with physical symptoms, but could be acting strangely – or vice versa. To tell if a molly fish is dying, look for the following physical signs and behaviors in your fish.

The following behaviors are signs that a molly fish is unwell and possibly dying:

  • Not eating
  • Hiding near the bottom of the tank
  • Rapid breathing
  • Shaking or shimmying (rocking from side to side, like a snake)
  • Gasping for air at the surface of the water
  • Swimming on their side
  • Difficulty swimming or erratic swimming
  • Keeping their fins clamped against their body
  • Floating to the surface of the water after swimming to the bottom of the tank
  • Descending to the bottom of the tank after swimming to the top
  • Scratching against the substrate at the bottom of the tank

Look out for the following physical symptoms to tell if a molly fish is dying:

  • Sunken, bulging, or cloudy eyes
  • Swollen gills
  • Lesions on the skin
  • Black, red, or white spots on the body
  • Fin rot
  • Tumors or growths on the body
  • Bright red mouth and anus
  • Bloating or swelling of the body
  • Scales that are sticking out 

On their own, these behaviors and physical symptoms may not mean the fish is dying. However, if you see a few of these signs, the fish is likely very sick or in the process of dying. 

Do Molly Fish Play Dead?

Some fish like to play dead! For example, some cichlid species pretend to be dead to lure other fish toward them. When the other fish approaches, the cichlid attacks and eats the other fish. 

You might be wondering if your listless molly fish is simply playing dead. 

Mollies, however, are not a species that exhibits this behavior. Mollies do not play dead, so if you see your molly fish lying on its side, it definitely indicates a problem! 

What Are The Most Common Causes Of Death In Molly Fish?

Molly fish are more prone to diseases and parasites when they live in poor water conditions or when their tank is overcrowded. 

The most common health issues that lead to death in molly fish are:

  • Ich or white spot disease – this disease is caused by an external parasite. Fish with ich have tiny white spots on their body and gills. Infected fish rub themselves on tank décor and substrate. Fish also tend to hide and avoid feeding. 
  • Dropsy – this bacterial infection causes a molly fish’s belly to bloat. They develop a curved spine and ulcers along the length of their body. The eyes bulge and turn cloudy, the gills look pale, and the scales become raised and stick out. 
  • Molly disease (AKA livebearer disease) – this condition is also called the “shimmies” because it causes fish to rock from side to side like a snake and twitch or shake. It is caused by poor water conditions. Affected fish keep their fins clamped to their bodies, and they have difficulty breathing. 
  • Velvet disease – this illness is caused by a parasite. Fish that have the disease have difficulty breathing and develop a red-brown film on their skin. The fish’s colors appear faded, and they rub themselves on objects in the tank. In severe cases, the fish’s skin starts to peel off. 
  • Columnaris – this bacterial disease causes mollies to develop white cotton-like growths around their mouth and on their fins and scales. The infection causes the fins to become ragged, and they develop ulcers on their skin. 
  • Camallanus worms – these internal parasites cause mollies to stop eating. Their abdomens become bloated, and red worms come out of their anus. 
  • Fish tuberculosis – this bacterial disease causes a molly’s tail and fins to rot, their colors to fade, and ulcers on their body and around their anus. An early symptom is a loss of appetite. 
  • Gill flukes – this is caused by a tiny, white, worm-like parasite that burrows into fishes’ gills. Fish have difficulty breathing and gasp for air at the water’s surface or on the bottom of the tank. In advanced cases, fish bleed from their gills. 

Can You Save A Molly Fish That Is Dying?

If a molly fish is in the early stages of an infection or disease, it is, in some cases, possible to treat it and save it from dying. However, sadly, some fish diseases are incurable, so you cannot save the fish from dying. 

The following diseases can be treated if detected early enough:

  • Ich/white spot disease
  • Molly disease/shimmies
  • Velvet disease
  • Columnaris
  • Camallanus worms
  • Gill flukes

The following diseases are not treatable and will lead to a molly fish dying:

  • Dropsy
  • Fish tuberculosis

How To Save A Dying Molly Fish

Once you have determined what disease or infection the molly fish has, you can take certain steps to try to save the fish from dying. 

If a molly fish is suffering from ich, first increase the temperature of the tank gradually to 80 degrees F. Then, treat the tank with a medication like Seachem Paraguard. Follow the instructions on the label closely! Do a major water change (at least 70%) and thoroughly clean the tank substrate

To treat early-stage molly disease (the shimmies), you must test the tank water. Ensure that the water parameters are perfect. The pH should be between 7 and 8, and the temperature should be between 76 and 80 degrees F. If the water is soft, add minerals to it with products like Seachem Equilibrium. 

Velvet disease can be treated using a copper medication like Seachem Cupramine. It’s a good idea to switch the tank lights off for the duration of the treatment. Once you cannot see any signs of the disease, you must do a major water change (70%). 

If a molly fish is showing symptoms of columnaris, you must isolate the fish in a hospital tank to prevent the other fish from getting infected. Keep the water temperature below 75 degrees F to prevent columnaris from spreading. Treat the fish with a medication like Seachem Polyguard.

Camallanus worms and gill flukes must be treated with medication like Fritz Expel-P. After treatment, you must perform a major water change (at least 90%), and you must repeat the treatment after three weeks. 

Why Do My Molly Fish Keep Dying?

If you are struggling to keep your mollies alive, the problem is likely related to the water quality or parameters. 

It is critical to do weekly water changes and clean the tank regularly. You must test the tank water regularly to check that all the water temperature and other parameters are appropriate for your fish. Cycling the tank water is also central to maintaining good water quality. 

Be very careful when adding new plants or fish to your aquarium. Newcomers must be quarantined and treated before you introduce them into the tank. Live foods can also be sources of disease. 

Ensure that your aquarium has a good filtration system and always remove decaying plant matter, uneaten food, and dead fish from the tank. 


Molly fish are a wonderful addition to your aquarium (though not necessarily best for beginners). If you are wondering if your fish is ill, or how to tell if your Molly fish is dying, be sure to assess both physical signs and changes in behavior. The good news is that there are treatments for sick molly fish, but we recommend keeping a close eye on water quality to prevent your mollies from becoming ill in the first place.

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