Why Is My Angelfish’s Mouth Stuck Open? (5 Easy Solutions)

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Angelfish are quite hardy and a favorite among many fish enthusiasts. They’re stunning to look at, and their behaviors are quite fascinating.

However, from time to time, they can face some troubles. I remember once noticing one of my angelfish keeping its mouth wide open, which had me concerned.

Luckily, after some research and experience, I found a way to address that issue. Let’s dive right into it.

Is it Normal for Angelfish to Keep Their Mouth Wide Open?

No, it is not normal for angelfish to keep their mouth wide open.

This behavior could indicate respiratory distress or a problem with the water quality in their tank.

It’s important to check the water parameters and consult a veterinarian specialized in fish if this behavior persists.

Why is My Angelfish Keeping Its Mouth Wide Open?

Several reasons can cause your angelfish to keep its mouth wide open. Consider the following:

1. Muscle Paralysis or Damage

Angelfish can suffer from muscle paralysis or damage, which may prevent them from closing their mouths properly.

This condition can be due to injuries from fights, collisions with tank decorations, or genetic issues.

  • Physical Injury: When angelfish collide with tank decorations or engage in aggressive behavior, they can injure the muscles around their mouths, leading to difficulty in closing it.
  • Genetic Defects: Some angelfish might have genetic deformities affecting their muscle control, resulting in an inability to close their mouth effectively.
  • Identification: Besides an open mouth, affected fish may exhibit unusual swimming patterns, such as difficulty maintaining buoyancy or tilting to one side.

2. Infection or Inflammation

Infections or inflammations in the mouth or gills can cause an angelfish to keep its mouth open.

This is often a result of bacterial or fungal infections which can swell the tissues, making mouth closure difficult.

  • Bacterial/Fungal Infection: Bacteria or fungi can infect the mouth or gills, leading to inflammation and swelling, forcing the mouth to remain open.
  • Inflammation of Tissues: Inflammation can occur in the gills or mouth, often visible as redness or swelling, which can hinder the normal mouth movement.
  • Identification: Look for other signs of infection such as lethargy, loss of appetite, or unusual spots or discoloration on the body or fins.

3. Improper Water Conditions

Angelfish require specific water conditions, and any imbalance can lead to stress and health issues, including respiratory distress that may cause them to keep their mouth open.

  • High Ammonia/Nitrite Levels: Elevated levels of ammonia or nitrites in the water can lead to respiratory distress, causing angelfish to gasp for air with an open mouth.
  • Low Oxygen Levels: Insufficient oxygen in the water can force angelfish to breathe more rapidly, resulting in an open mouth as they attempt to intake more oxygen.
  • Identification: Test the water for ammonia, nitrite, pH levels, and oxygen levels; also look for signs like rapid gill movement or gasping at the water’s surface.

For a better understanding, here’s a table explaining different oxygen levels in home aquariums and the survival probability for each range:

Oxygen Level (mg/L)Survival Probability
0-2Very Low – Immediate danger, rapid fish death likely
2-4Low – Stressful for most fish, survival is compromised
4-6Moderate – Tolerable for many fish, but not ideal
6-8High – Ideal for most freshwater fish species
8-10Very High – Excellent, often found in well-aerated tanks

Also Read: Stress In Angelfish

4. Foreign Object Lodged in Mouth

Angelfish can accidentally ingest or get small objects lodged in their mouth, which can prevent them from closing it properly.

  • Ingestion of Debris: Small gravel, tank decorations, or food pieces that are too large can get stuck in the angelfish’s mouth, keeping it ajar.
  • Obstruction in Mouth: Objects lodged inside the mouth can be visible upon close inspection and might prevent normal mouth movement.
  • Identification: Apart from an open mouth, the fish might also try to rub its face against tank objects to dislodge the foreign object.

5. Nutritional Deficiencies

A lack of essential nutrients in an angelfish’s diet can lead to health problems, including issues with muscle function, which may result in an inability to close their mouth.

  • Lack of Essential Nutrients: Insufficient vitamins and minerals in the diet can weaken muscle function, affecting the ability to close the mouth.
  • Poor Diet Quality: A diet lacking in variety or essential nutrients can lead to overall poor health and muscle weakness in angelfish.
  • Identification: Look for other signs like fading colors, lethargy, or a refusal to eat, which can indicate nutritional deficiencies.

How to Help Angelfish That Continuously Keep Their Mouths Open

Here are some steps to take if your angelfish has its mouth open:

1. Administering Antibiotics for Infections

If an angelfish is keeping its mouth open due to an infection, using a broad-spectrum treatment like Seachem PolyGuard (link to Amazon) can be effective.

This medication is known for treating a wide range of infections including bacterial, fungal, and parasitic issues.

  • Consult a Vet: Before using Seachem PolyGuard, consult with a vet to confirm it’s suitable for your fish’s specific condition.
  • Dosage Instructions: Follow the package instructions for Seachem PolyGuard, typically one measure (included in the package) per 40 liters (10 gallons) of water.
  • Treatment Duration: Treat for 5-7 days and observe the fish’s response; extend treatment if necessary but not beyond two weeks.
  • Water Changes: Perform regular water changes, about 20-30% before each dose, to maintain water quality and effectiveness of the medication.

Also Read: Angelfish Diseases

2. Providing Nutritional Supplements

Nutritional deficiencies can contribute to health issues in angelfish, including muscle problems. Ensuring a diet rich in essential nutrients is crucial for their overall health.

  • Balanced Diet: Include a variety of foods like high-quality flakes, frozen or live brine shrimp, and spirulina, to provide essential nutrients and vitamins.
  • Specific Supplements: Consider adding vitamin and mineral supplements to the diet, especially if the fish shows signs of nutritional deficiencies. For this purpose, I personally got the Seachem Nourish (link to Amazon).
  • Regular Feeding Schedule: Maintain a consistent feeding schedule, offering small amounts 2-3 times a day to ensure proper nutrition without overfeeding.
  • Monitor Fish’s Health: Keep an eye on the fish’s appearance and behavior as dietary changes are made to ensure they are benefiting from the new regimen.

Also Read: How To Feed Angelfish

3. Adjusting Water Conditions and Quality

Proper water conditions are vital for the health of angelfish, especially when they are showing signs of stress like keeping their mouths open.

Maintaining optimal water parameters can significantly improve their living conditions and health.

  • Test Water Regularly: Use water testing kits to regularly check parameters like pH, ammonia, nitrites, and nitrates, aiming for a pH of 6.5-7.5 and ammonia/nitrites at 0 ppm.
  • Aerate the Water: Ensure adequate oxygenation by using air stones or powerful filters, as low oxygen levels can cause respiratory distress in fish. My recommendation: Hygger Aquarium Air Stone (link to Amazon).
  • Regular Water Changes: Perform weekly water changes of about 20-30% to keep the water clean and reduce the buildup of harmful substances.
  • Temperature Control: Maintain a stable water temperature suitable for angelfish, typically between 76-82°F (24-28°C), as temperature fluctuations can cause stress.

Also Read: Angelfish Water Parameters

4. Removing Foreign Objects

If a foreign object is lodged in an angelfish’s mouth, it’s crucial to remove it carefully to prevent further injury or stress.

  • Visual Inspection: Gently catch the fish and inspect its mouth for visible objects like gravel or tank decorations; use a magnifying glass if needed for a closer look.
  • Gentle Removal: If an object is found, use tweezers or similar tools to carefully remove it, taking care not to injure the fish.
  • Quarantine After Removal: Place the fish in a quarantine tank for observation after removal to ensure no infection develops and to allow for recovery.
  • Prevent Recurrence: Adjust the tank setup to prevent similar incidents, like using larger gravel that cannot be ingested or removing small, sharp decorations.

5. Supportive Care for Muscle Paralysis or Damage

Muscle paralysis or damage in angelfish can be challenging to treat, but supportive care can improve their quality of life and potentially aid in recovery.

  • Reduce Stress: Keep the tank environment calm with minimal disturbances, as stress can exacerbate muscle issues.
  • Nutritional Support: Provide easily digestible, high-quality food to ensure the fish receives adequate nutrition without exerting too much effort.
  • Gentle Handling: If handling is necessary, do so gently and minimize the time the fish is out of water to avoid additional stress or injury.
  • Monitor Closely: Regularly observe the fish for any changes in behavior or appearance, and consult a vet if there is no improvement or if the condition worsens.

Also Read: Angelfish Swimming Erratically

What is Mouth Fungus in Angelfish?

Mouth fungus in angelfish, commonly mistaken for a fungal infection, is usually caused by the bacterium Flavobacterium columnare.

It appears as white or grayish cotton-like growths around the mouth and other parts of the body.

While Seachem PolyGuard is effective against a wide range of infections, it is not specifically designed to treat mouth fungus caused by Flavobacterium columnare.

In such cases, it’s advisable to consult a vet for the appropriate medication and treatment.

Will a Hungry Angelfish Keep Its Mouth Open?

No, a hungry angelfish typically does not keep its mouth open as a sign of hunger.

Instead, hunger is more often indicated by more active searching for food and a heightened response to feeding stimuli.

Angelfish keeping their mouths open is generally a sign of stress or health issues, not hunger.

Also Read: Why Do Angelfish Hide?


For quick readers, here’s a short summary:

  • Angelfish with open mouths are not normal, signaling potential health issues or poor water quality.
  • Muscle damage, physical injury, genetic defects, infections, or foreign objects can cause open mouths in angelfish.
  • To help angelfish, administer antibiotics for infections, provide proper nutrition, adjust water conditions, and remove foreign objects.
  • Mouth fungus in angelfish is caused by bacteria, not hunger, and may require specific treatment from a vet.
  • Hungry angelfish do not typically keep their mouths open; open mouths are more likely a sign of stress or health problems.