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Sick Fish? Here's How to Know...

Your Fish Will Let You Know When They’re Not Feeling Well

Spotting a healthy fish is a breeze. They’ll swim with ease, display vibrant colors, have a hearty appetite, and their appearance will be normal and well-proportioned.
In other words, it’s pretty straightforward to notice even the earliest signs that your fish might not be feeling their best.

Key Indicators That Your Fish Might Be Unwell

By regularly checking on your tank and fish, you’ll become familiar with your fish’s usual habits and behaviors. Here are some red flags to keep an eye out for:

Changes in Appetite

Variations in feeding, such as loss of appetite, lethargic feeding, or completely ignoring food, are signs that something might be off.

Changes in Physical Appearance

Any noticeable physical changes should be investigated, including swelling, spots, speckles, pimples, or sores on the body or fins. Signs of health issues can also include flattened, clamped, or tattered fins, discoloration (especially gray, white, and yellow), and fuzzy or cottony growths on the body or around the mouth.

Changes in Behavior

If your fish isn’t acting like its usual self, this could also signal potential problems. Changes in behavior can include rapid breathing, gasping, excessive gill movement, sinking or lying on the bottom of the tank, loss of buoyancy, listing side to side, scratching against rough surfaces, and gasping at the surface.

Symptoms can point to a variety of infections and illnesses.

Identifying the cause of symptoms is a crucial step in figuring out how to treat the fish. Depending on the diagnosis, the first step might be to remove the sick fish from the community tank for treatment.

In other cases, the entire tank might need to be treated. If detected early, many fish health issues can be treated and resolved. There are many multi-symptom antibiotics and treatments available commercially.

Fish Illnesses Can Be Grouped into Several Categories:


Parasite Infections

Many times, parasitic infections come from external sources, mainly from new fish and plants that haven’t been properly quarantined and treated before being added to the tank.

Fungal Illnesses

Fungal illnesses mainly affect the external parts of the fish. They often start due to poor water conditions in the tank, although there can be other causes such as infection from a tankmate.

Bacterial Illnesses

Bacterial illnesses can affect both the external and internal parts of the fish and are usually caused by harmful bacteria that already exist in every aquarium. When a fish is stressed, their ability to maintain a slime coat barrier is compromised, This can lead to opportunistic infections that a fish may not be able to fight off.

Bacterial infections are among the most common illnesses seen in aquarium fish.

Injuries, Situational Illnesses, and Cancers

Injuries, situational illnesses, and cancers can happen as well. Many illnesses are simply caused by stress: changes in water parameters or dynamics between the tank inhabitants can also trigger unusual behavior and ailments. It could even be poor nutrition.

Examples of Common Illnesses and Their Symptoms:

Ich (Ichthyophthirius)

Ich is the most common parasite infection, typically caused by poor water conditions and fish stress. The most common symptoms are white grain-of-salt spots all over the fish’s body, rapid gill movement or surface breathing and gasping, scratching against substrate or sand due to skin irritation, and clamped fins.

If caught reasonably early, this disease can be easily treated with, and sometimes without, medication. I typically raise the tank's temperature to 82f and salt the water at a rate of 1tb per gallon. This can be hard on many plants and some inverts and fish. Use caution, and do it gradually. Effective medication we also use is Ich-x.

Red Pest (Hemorrhagic Septicemia), Fin Rot, and Mouth Fungus (Columnaris)

These bacterial infections will cause fins to appear tattered, body changes including swelling and bulging eyes, and fuzzy spots on the skin and mouth.

Medication is required to treat this condition. We like Maracyn with Ich-X. The Malachite Green is a powerful ingredient for fungus.


Dropsy is typically characterized by bloating and often indicated by swelling and protruding scales due to an excess of fluids in the body.

It is usually a symptom of another bacterial issue, generally related to the kidneys. Even with strict maintenance and medication, this disease is usually fatal.

Velvet, Rust, or Gold Dust Disease

Also known as oodinium, these dinoflagellate parasites can appear as a yellow to rust-colored dusting on the body of the infected fish. The fish may also display behaviors like scratching, gasping, or deteriorating gills or fins.

Velvet is quite persistent, but with proper treatment involving heightened maintenance and possibly medication, it can be successfully eliminated. Increasing the water temperature and removing lighting help in treating velvet.

Prevention is Better Than Cure

The most effective ways to prevent fish sickness include developing regular routines for dipping and quarantining before introducing new tank inhabitants, testing water conditions, and conducting regular partial water changes to ensure that minor changes are corrected before they impact your tank. It’s also crucial to avoid overfeeding. Fish need less than most of us think.

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