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Stress In Molly Fish: 15 Symptoms And Solutions

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Molly fish are extremely peaceful and easy to care for, which is why many fish owners, including myself, choose to raise them in their tanks.

However, like any other fish, they can become stressed for various reasons.

Unfortunately, identifying the underlying cause might be a little challenging, which is why I decided to write this article.

Here, I will discuss 15 common symptoms of stressed mollies and provide detailed instructions on how to address each one.

So, without further ado, let’s get started.

Also Read: Molly Fish Care Guide

1. Gasping Near the Water Surface

Gasping near the water surface indicates that molly fish are struggling to intake oxygen. This can result from poor water quality, low oxygen levels, or potential respiratory diseases.

How to Treat

  • Install an Air Pump: Enhance aeration using a 5-watt air pump or an airstone in a 30-gallon tank, as more oxygen reduces stress.
  • Observe for Disease Symptoms: Red or swollen gills, excess mucus, or uncoordinated swimming might point to a respiratory disease. Seek veterinary help if such symptoms are noticed.
  • Monitor Population Density: Overcrowding can lead to oxygen depletion. A good rule of thumb is one molly fish per 3 gallons of water.
  • Change Water Regularly: A weekly 15-20% water change helps maintain a fresh, oxygen-rich environment.
  • Seek Professional Help: If gasping persists despite these efforts, contact an aquatic veterinarian for further advice.

Also Read: Why Is My Molly Fish Gasping For Air?

2. Loss of Appetite

Loss of appetite in molly fish can result from several stressors like illness, poor water conditions, or aggressive tank mates.

Lack of appetite can lead to weight loss and weakened immunity, making the fish more susceptible to diseases.

How to Treat

  • Diversify Diet: Offer a variety of high-quality flakes, pellets, and live or frozen foods like bloodworms or daphnia to stimulate appetite.
  • Monitor for Disease Symptoms: If the fish is lethargic, showing changes in color, or experiencing abnormal swimming, it might be ill. Consult a vet if these signs are observed.
  • Create a Safe Environment: Segregate hostile fish or add more hiding spots to reduce stress. Aquarium plants or terracotta pots can serve as refuges.
  • Control Feeding Habits: Overfeeding can also lead to loss of appetite. Fish should consume food within 2-3 minutes, twice a day.
  • Maintain Optimal Conditions: Regular water changes and maintaining a temperature around 72-78°F will provide a suitable environment for feeding.

Also Read: Why Is My Molly Fish Not Eating?

3. Engaging in Glass Surfing

Glass surfing in molly fish, when they swim up and down the tank sides, suggests stress due to poor water quality, reflection stress, or boredom.

Prolonged glass surfing can lead to exhaustion and increased susceptibility to diseases.

How to Treat

  • Rearrange the Tank: Change the aquarium layout or add new elements every few months to keep the environment engaging.
  • Reduce Reflections: Place the aquarium in a location where the fish isn’t exposed to its reflection constantly. Reflections might be perceived as other fish, causing stress.
  • Check Water Quality: Maintain a pH around 7.0-7.8. Elevated levels of ammonia, nitrate, or nitrite can cause stress. I personally check those with the API FRESHWATER MASTER TEST (link to Amazon).
  • Create Enriching Environment: Introduce live plants or aquarium-safe toys for stimulation. A mix of Java ferns, moss balls, and tunnels can keep mollies entertained.
  • Monitor Tank Mates: Aggressive or overly active tank mates can stress mollies. Keep a close eye on tank dynamics and intervene if required.

4. Twitching and Shivering

Twitching and shivering in molly fish often indicate stress, possibly due to water temperature fluctuations, electrocution risks, or parasites.

This involuntary movement can cause significant energy loss and impact their overall health.

How to Treat

  • Maintain Stable Temperature: Sudden temperature changes can cause twitching. Maintain a stable range between 72-78°F using a reliable heater. My recommendation: Orlushy Submersible Aquarium Heater (link to Amazon).
  • Check for Electrocution Risks: Ensure no equipment is leaking electricity into the water. Use a grounding probe to prevent electrical accidents.
  • Inspect for Parasites: Parasites like Ich can cause twitching. Look for white spots or a velvet-like sheen on the fish’s body.
  • Administer Parasite Treatment: If parasites are identified, apply a suitable treatment like Fritz Mardel (link to Amazon) or copper-based medications for Velvet.
  • Observe and Consult a Vet: If twitching continues despite interventions, consult a vet to diagnose and treat any underlying conditions.

Also Read: Why Is My Molly Shaking?

5. Seeking Refuge and Hiding

Molly fish seeking refuge or hiding excessively might be stressed due to aggressive tank mates, bright lighting, or lack of suitable hiding places.

This can lead to less social interaction and impaired feeding habits.

How to Treat

  • Provide Adequate Hiding Spots: Use live plants, caves, or aquarium-safe decorations to create multiple hiding spots. Floating plants can provide shade, helping mollies feel secure.
  • Adjust Lighting: Intense lighting can stress fish. Use a timer to mimic a natural day-night cycle with 8-10 hours of light per day.
  • Monitor Tank Mates: Aggressive fish can stress mollies. If a fish is causing stress, consider segregating it or adjusting tank dynamics.
  • Check for Illness: Hiding can also indicate illness. Look for other symptoms like color changes or abnormal swimming.
  • Regularly Observe Behavior: Keep a close eye on the molly fish. If excessive hiding persists, a vet consultation might be necessary.

Also Read: Why Is My Molly Hiding?

6. Fading of Colors

Fading of colors in molly fish is a stress indicator, possibly due to poor nutrition, lack of light, or illness.

It can also be a normal response to night-time or a way to avoid conflict with aggressive fish.

Also Read: Why Is My Molly Fish Turning White?

How to Treat

  • Offer Balanced Diet: High-quality fish food, rich in vitamins and minerals, can enhance coloration. For instance, foods high in carotenoids can boost color vibrancy.
  • Ensure Proper Lighting: An 8-10 hour light cycle per day helps maintain fish coloration. Too much or too little light can fade colors.
  • Monitor for Illness: Color fading can be a sign of disease. If accompanied by lethargy, loss of appetite, or other changes, seek a vet’s advice.
  • Adjust Tank Environment: High stress levels can cause color fading. Maintain a peaceful tank environment with adequate hiding spots.
  • Avoid Overcrowding: A crowded tank can cause stress leading to color fading. Keep one molly fish per 3 gallons of water as a general rule.

Also Read: Do Molly Fish Change Color?

7. Chasing and Harassing Other Fish

Chasing and harassing other fish might be a sign of stress in molly fish, often due to mating behavior or territory disputes.

This can lead to the stressed fish and others in the tank becoming exhausted, injured, or diseased.

How to Treat

  • Ensure Proper Sex Ratio: A ratio of two or three females per male can reduce aggression. Males can stress females with excessive mating attempts.
  • Provide Adequate Space: Overcrowding can increase aggression. A larger tank or fewer fish can help mollies establish territories without conflict.
  • Introduce Hiding Places: Plenty of plants, caves, or aquarium decorations can provide refuges for mollies being chased.
  • Separate Aggressive Fish: If a particular fish is consistently causing stress, consider removing it from the tank temporarily.
  • Monitor Fish Behavior: Keep an eye on tank dynamics, and intervene if any fish is consistently being harassed or shows signs of injury.

Also Read: Molly Fish Bullying & Attacking Other Fish

8. Deterioration and Degradation of Fins

Deterioration and degradation of fins in molly fish can result from fin-nipping tank mates, poor water quality, or diseases like fin rot.

This can inhibit swimming, impair feeding, and leave the fish vulnerable to other diseases.

How to Treat

  • Identify and Separate Fin-Nippers: If certain fish are consistently causing damage, it may be necessary to separate them to protect your mollies.
  • Maintain Clean Water: Regular water changes and effective filtration can prevent diseases like fin rot. Replace 10-15% of the tank water weekly.
  • Administer Medication: Treat fin rot with antibacterial medications such as API MELAFIX (link to Amazon) as per the product’s instructions.
  • Monitor for Regrowth: Healthy fins should start to regrow within a week or two. If not, seek veterinary assistance.
  • Ensure Balanced Diet: A diet rich in vitamins and minerals, especially vitamin C, can promote fin health and recovery.

Also Read: Molly Fish Diseases

9. Rubbing Against Gravel or Decorations

Rubbing against gravel or decorations, also known as “flashing”, may indicate that molly fish are stressed due to parasites or poor water quality.

This behavior can lead to skin damage and secondary infections.

How to Treat

  • Check for Parasites: Look for signs of parasites like white spots, redness, or mucus. If parasites are identified, treat with an appropriate medication like API General Cure (link to Amazon).
  • Maintain Water Quality: High levels of ammonia or nitrite can irritate mollies’ skin. Regularly test the water and change 15-20% weekly.
  • Remove Sharp Decorations: Sharp or rough decorations can injure fish. Use smooth, aquarium-safe decorations to minimize injury risk.
  • Offer a Salt Bath: A brief salt bath using 1-2 tablespoons of aquarium salt per gallon can help soothe irritated skin.
  • Consult a Vet: If flashing persists despite interventions, consult a vet to diagnose and treat any underlying issues.

Also Read: 15 Things You Should Know About Molly Fish

10. Turning Black

Molly fish turning black can indicate stress from genetics, aging, or illness. This color change can occur gradually or suddenly, depending on the cause.

How to Treat

  • Monitor for Sudden Changes: If the color change happens abruptly, it may indicate stress or illness. In this case, seek a vet’s advice.
  • Provide a Balanced Diet: Feeding a balanced diet rich in vitamins can help mollies maintain their color.
  • Test Water Quality: Maintaining a pH between 7.0-7.8 and temperature around 72-78°F can help mollies stay healthy and retain their color.
  • Check for Illness: If color change is accompanied by other symptoms such as lethargy or loss of appetite, it might be due to disease.
  • Observe Aging Fish: Color change can be part of the natural aging process in mollies, especially if it occurs gradually.

Also Read: Why Is My Molly Turning Black?

11. Lack of Movement

Molly fish showing lack of movement or remaining stationary for long periods might be stressed due to poor water quality, illness, or lack of stimulation.

This can lead to muscle atrophy and increased susceptibility to diseases.

How to Treat

  • Enhance Tank Environment: Add live plants or decorations to provide stimulation. Use items like tunnels, caves, or even a mirror for short periods.
  • Maintain Optimal Conditions: Regular water changes and maintaining the tank temperature around 72-78°F can help mollies stay active.
  • Monitor for Disease: If the fish is also showing signs like color changes or loss of appetite, it might be sick and require veterinary attention.
  • Offer Varied Diet: Provide a balanced diet with a mix of high-quality flakes, pellets, and live or frozen foods to stimulate activity.
  • Check Tank Population: Overcrowding can cause stress and lethargy. Ensure the tank isn’t overpopulated, keeping one molly fish per 3 gallons of water.

Also Read: Why Is My Molly Not Moving?

12. Staying at the Bottom

If molly fish are consistently staying at the bottom of the tank, they might be stressed due to poor water quality, illness, or aggressive tank mates.

This behavior can impair their feeding and interaction with other fish.

How to Treat

  • Test Water Quality: Monitor the tank’s nitrate, nitrite, and ammonia levels. Regular water changes can help maintain optimal conditions.
  • Monitor for Disease: Look for other symptoms like discoloration or abnormal swimming. If present, consult a vet.
  • Check Tank Mates: Aggressive fish can stress mollies, causing them to hide at the bottom. Consider segregating aggressive fish if necessary.
  • Provide Hiding Places: Adding live plants, caves, or aquarium decorations can provide mollies with a sense of security and reduce stress.
  • Maintain Optimal Temperature: Sudden temperature drops can cause mollies to stay at the bottom. Ensure the tank’s temperature remains around 72-78°F.

Also Read: Why Do Molly Fish Stay At The Bottom Of The Tank?

13. Staying at the Top

Molly fish consistently staying at the top of the tank might be stressed due to low oxygen levels, poor water quality, or potential diseases.

This behavior can lead to reduced activity and increased vulnerability to diseases.

How to Treat

  • Increase Oxygen Levels: Enhance aeration using an air pump or adding live plants to the tank. My recommendation: Hygger Aquarium Air Stone (link to Amazon).
  • Check Water Quality: Regularly test water parameters like pH, ammonia, and nitrite levels. A weekly water change of 15-20% can help maintain optimal conditions.
  • Look for Disease Symptoms: If staying at the top is accompanied by other symptoms like loss of appetite or abnormal swimming, consult a vet.
  • Regulate Population: Overcrowding can cause low oxygen levels. Follow the rule of thumb of one molly fish per 3 gallons of water.
  • Observe for Gasping: If the fish is gasping at the top, it might need immediate veterinary attention.

Also Read: Molly Fish Staying At The Top Of The Tank

14. Blowing Bubbles Persistently

Persistent bubble-blowing in molly fish can indicate stress due to breeding behaviors, lack of oxygen, or as a response to certain medications.

It might interfere with their feeding and regular activities.

How to Treat

  • Monitor Breeding Behavior: If mollies are healthy and the water conditions are optimal, bubble blowing might be a sign of breeding behavior.
  • Improve Oxygenation: Use an air pump or airstone, particularly in larger tanks, to ensure sufficient oxygen levels. My recommendation: Tetra Whisper Air Pump (link to Amazon).
  • Assess Medication Effects: If bubble-blowing started after a medication was introduced, consult a vet for advice.
  • Check Water Parameters: Regular water changes and testing for pH, nitrite, nitrate, and ammonia levels can help ensure a healthy environment.
  • Consult a Vet: If bubble-blowing persists despite these steps, seek professional advice.

Also Read: Why Is My Molly Fish Blowing Bubbles?

15. Breathing Fast

Fast breathing in molly fish can indicate stress due to low oxygen levels, poor water conditions, or potential diseases.

This can lead to exhaustion and increased vulnerability to other illnesses.

How to Treat

  • Increase Tank Oxygenation: Enhance oxygenation by using an air pump, waterfall feature, or live plants that produce oxygen.
  • Maintain Optimal Water Quality: Regular water changes and maintaining a stable temperature around 72-78°F can reduce stress.
  • Look for Disease Symptoms: Rapid breathing can also be due to diseases like gill flukes or bacterial infections. Consult a vet if other symptoms are present.
  • Control Tank Population: Overcrowding can lead to low oxygen levels, causing mollies to breathe fast. Keep one molly fish per 3 gallons of water.
  • Provide a Calm Environment: Excessive noise or movement outside the tank can stress mollies, leading to fast breathing. Minimize disturbances around the aquarium.

Also Read: Why Is My Molly Fish Breathing Fast?


If you notice any of the signs mentioned above in your molly fish, make sure not to ignore them.

These symptoms usually indicate that your fish is going through a tough time and needs your help. If you’re not sure what to do, don’t hesitate to reach out to an aquatic veterinarian.

Seeking guidance from an expert is always the best choice when you need assistance with your beloved fishy friend.