Today, you will learn about 12 common diseases that affect saltwater fish.
In addition, you will learn the underlying cause of each illness and HOW to treat the problem.
And before you go, scroll to the bottom to learn how to easily prevent most saltwater fish diseases on this list!
12 Common Saltwater Fish Diseases:
#1. Ich
Symptoms:
- Ich, or White Spot Disease, is a tiny outbreak of white spots dotted across the body of your saltwater fish that usually begins around the gills and fins.
- It appears like grains of sand or salt, usually measuring about 2mm in diameter.
- Fish will typically try to rub their skin against the glass to alleviate the itchy sensation.
- Other symptoms can include labored breathing if the spots are located on the gills, difficulty swimming due to folded fins, and loss of appetite.
What are the causes of Ich?
- Tiny parasites of either Cryptocaryon or Oodinium cause this disease in saltwater fish. The white spots you see are individual parasites located just beneath the fish’s transparent skin.
- New fish added to your tank are the main culprit for an Ich infestation, so it’s imperative that you quarantine them for a few weeks until you know they are healthy.
- Another cause of ich is poor water quality due to poorly maintained tanks or a sudden drop in temperature, which both cause stress.
How do you treat Ich?
- I have personally used API Liquid Super Ick Cure before. First, remove activated carbon from the filter, and then add 1 teaspoon for every 5 gallons of aquarium water. Repeat the dose after 48 hours and then change 25% of the water.
- You should also increase the water temperature to as high as 82 degrees Fahrenheit (27 C). The warmer the water, the faster the life cycle of the parasite progresses. Specifically, the little white spots on your fish eventually mature, break through the skin, and fall to the aquarium floor. The Ich treatment you added only works on the parasites that are free-swimming in the water, so you need them to get into the water while it’s being medicated to kill them.
Ich is very common and one of the only fish parasites you can see with your naked eye. As long as you catch the symptoms early and start treatment right away, then you should be able to save your saltwater fish. If you don’t intervene, then it will likely die.
#2. Fin Rot
Symptoms:
- Stumpy, frayed, ragged, or split fins.
- The fin often has a white edge (black or brown in some cases) on them.
- Fin rot can cause weakness and lethargy in saltwater fish, including loss of appetite and death in advanced cases.
What causes Fin Rot?
- Bacteria, such as Flavobacterium, Aeromonas, and Pseudomonas, are typically to blame.
- Fin Rot usually affects saltwater fish that are in poor condition or have weak immune systems. For example, fighting (fin nipping), poor water conditions, poor nutrition, overcrowding, overfeeding, or new fish that were handled roughly can lead to Fin Rot.
What is the treatment for Fin Rot?
- Move the infected individual to a separate treatment tank. If all the fish show symptoms, this step is unnecessary, and you can treat all the fish together.
- Infections are relatively easy to cure. Treat your aquarium with an antibacterial, such as API Marine Melafix or API PIMAFIX Antifungal.
- Check your saltwater fish every day to see if the Fin Rot has ceased. Once cured, you will see the fins and tail slowly start to grow back!
Luckily, if you act right away, you should be able to cure your saltwater fish of this disease. But you need to try and figure out the underlying cause of the illness. Is your tank overcrowded? Is your water quality poor? At the very least, I would do a partial water change immediately and test your water.
#3. Marine Velvet (Gold Dust Disease)
Symptoms:
- Marine Velvet disease gives the infected saltwater fish a dusty, brownish-gold color and will make the fish look gold coated or sometimes green or brown.
- It can cause excess slime production, causing the fish to have trouble breathing, loss of appetite, and general lethargy. The fish will often keep its fins along its sides.
- Oftentimes, you will see your fish rubbing itself against the object in the tank to alleviate the weird feeling.
What causes Marine Velvet disease?
- Velvet disease is caused by dinoflagellate parasites of the genera Amyloodinium.
- A dirty water tank and contaminated tools such as nets and testing supplies are often responsible for an outbreak.
How do you treat Velvet Disease?
- Quarantine the infected fish in a separate tank and raise the temperature to 82-86°F, which helps quicken the lifecycle of the velvet parasites.
- Medicate your tank with copper sulfate, methylene blue, formalin, or malachite green.
This disease is very contagious! If one individual gets infected by the disease, it can easily spread to the other fish in your tank, compromising every fish’s immune system. Early detection and immediate action are incredibly important.
#4. Hexamita (Hole-in-the-Head Disease)
Symptoms:
- Small holes appear on the body of your saltwater fish, especially near the head. These holes eventually turn into tubular eruptions. It sort of looks like something is eating the fish alive.
- Yellow strings of mucus that sort of look like worms often trail from the holes. This symptom has confused many people into thinking their fish was infested with worms.
- Sick fish will often stop eating and are lethargic. Their face is also more subdued than normal.
What causes Hexamita?
- The cause of this illness is unclear, but flagellate protozoans (Hexamita or Sprionucleus) have been involved in the past.
- It’s common for saltwater fish to have low-level infections of Hexamita in their intestines without doing the fish any harm. But certain factors, such as poor nutrition, overcrowding, low oxygen levels, bad water condition, or any other stressor, cause the parasites to multiply and develop into Hole-in-the-Head Disease.
How do you treat Hexamita?
- Using medicated fish food is a great way to treat this illness. Unfortunately, most affected saltwater fish have stopped eating, and it can be hard to mix medicated food on a small scale.
- Adding the drug metronidazole, which is designed to fight protozoan parasites like Hexamita, directly to the tank also works. Follow the directions closely to get the dosage correct.
To prevent Hole-in-the-Head Disease in saltwater fish, make sure to quarantine all new fish. Also, eliminate the contributing factors, such as poor water quality. When testing your water, aim for a nitrate concentration of less than 20 mg/l. Make sure not to overfeed and do a partial water change weekly.
#5. Gill Flukes
Symptoms:
- Look for the presence of spots or redness near the gills that look like a pimple. The spots will be redder in color than the surrounding skin.
- As the disease progresses, your fish will excrete mucus due to secondary infections in the respiratory tract.
- Other signs that your saltwater fish is suffering from this disease are lethargy, lack of appetite, difficulty in breathing, and low energy.
What causes Gill Flukes?
- Gill flukes are caused by a parasitic flatworm, which attaches to your fish’s gills or skin with microscopic hooks.
- Outbreaks typically occur when new fish are added to an aquarium without being quarantined first.
- Gill flukes also happen when your tank is improperly maintained and overcrowded.
What is the treatment for Gill Flukes?
- One of the most effective treatments for gill flukes is using a deworming medication such as Hikari Prazipro or PraziCura, which can also treat anchor worms and other fish parasites.
- Separate the infected fish from the others and put it in a quarantine tank where it can recover.
Without immediate treatment, your saltwater fish will eventually die from this disease. So it’s super important to observe your fish often and react quickly if you notice any of the symptoms of Gill Flukes. Luckily, if caught early, it’s quite possible to save your fish! And remember, the BEST way to prevent Gill Flukes is to quarantine new fish. 🙂
#6. Lymphocystis
Symptoms:
- Whitish growths on the fins and the back. Easily confused with Ich.
- The white bumps resemble cauliflower, which is how the disease got its nickname, “cauliflower disease.”
What causes Lymphocystis?
- Lymphocystis is a VIRAL infection.
- This disease is more common in tanks where saltwater fish are stressed due to poor water quality.
What is the treatment for Lymphocystis?
- Since this disease is viral, there is no cure. Your saltwater fish will carry the virus for the rest of its life.
- The best way to get rid of the whitish growths and keep the virus in remission is to make your tank environment as healthy as possible. Great diet, low stress, and great water chemistry.
#7. Anchor Worms
What causes Anchor Worms?
- Anchor worms are caused by small crustaceans that embed themselves into the scales and flesh of your fish.
- Stress, pH levels, overcrowding, and poor water conditions are all factors that increase the amount of these parasites.
Symptoms:
- Look for redness and inflammation at the spot where the crustaceans are embedded.
- You can see visible 25mm, stringy red or white-green worm-looking creatures at the base of the fins of your saltwater fish.
- Other symptoms include difficulty breathing and constantly rubbing against objects to alleviate the pain.
How do you treat anchor worms?
- The best treatment is a potassium permanganate bath, which will kill young anchor worms in the water and prevent them from embedding in your fish. Follow directions carefully because this stuff can be toxic in the wrong doses.
- If you can see anchor worms on your fish, you can remove them with tweezers. Make sure to remove the entire worm so nothing is left embedded in your fish’s skin.
Anchor worms cause damage to fish, but they are rarely the cause of death. Instead, the Anchor Worms will weaken your saltwater fish, which makes it susceptible to many other diseases and illnesses. Make sure to perform periodic water changes to keep the water in your aquarium as healthy as possible while your fish is healing.
#8. Uronema marinum
What are the symptoms of Uronema marinum?
- Red sores. These red sores typically form a vertical red line in the center of the body.
- Rapid breathing, weight loss, and loss of color.
What causes Uronema marinum?
- The saltwater parasite ciliated protozoa are responsible for this saltwater fish disease.
How do you treat Uronema marinum?
- Unfortunately, in most cases, once your fish has contracted Uronema marinum, euthanasia is recommended, especially if red sores have already appeared.
- But, if caught early enough, you can try to bathe your fish in a freshwater tank for 2-3 minutes. Or put it in a separate aquarium with low salinity (1.011) for 21 days.
- Another option is to use a chemical treatment, such as methylene blue, copper sulfate, or malachite green.
This parasite is VERY dangerous and nearly impossible to get rid of once it infects your tank. The parasites live freely in the aquarium when fish are not present, just waiting for their next host. The best way to prevent this dangerous disease is through prevention, especially quarantining new fish until you can guarantee they are healthy!
#9. Bacterial infections
Symptoms of a bacterial infection:
- The body appears red and sore.
- Eyes are cloudy.
- Tail and fin rot.
- Fungus growths or white film on the body.
What causes a bacterial infection?
- Typically, a bacterial infection arrives after another ailment, such as gill flukes or Ich.
- Any open wound is subject to getting infected.
How do you treat a bacterial infection?
- Treat for 7-10 days with a broad antibiotic, such as API PIMAFIX Antifungal or API Marine Melafix, since you’re not entirely sure which type of bacteria has infected your saltwater fish.
- Make sure to move your fish to a quarantine tank for treatment!
If you can’t figure out what is wrong with your saltwater fish, it may have some sort of bacterial infection, which can be extremely dangerous if not treated. Fish that have open wounds or are weak are especially susceptible.
#10. Internal parasites and infections
Symptoms:
- Your fish is skinny and can’t seem to gain weight.
- The belly appears that it is sinking in or bloated.
- Feces is white and stringy.
What causes an internal parasite or infection?
- This illness is common for new saltwater fish, especially if they were imported.
- The underlying ailment may be caused by worms, parasites, or a bacterial infection. Since you can’t look inside your fish, you can’t really determine what’s the exact problem.
How do you treat an internal parasite or infection?
- Use a broad medication, such as API General Cure or API Marine Melafix.
- Put the sick fish in a quarantine tank until it’s healthy.
#11. Swim bladder disorders
Symptoms:
- In general, your saltwater fish will have a floating problem and have difficulty maintaining its water position. It may float on its side or at the surface or even remain sunk on the bottom.
- Other than not being able to float property, the fish typically looks in good condition.
What causes a swim bladder disorder?
- The exact causes are poorly understood.
- There are thought to be various factors that can cause problems with the swim bladder, including microbial infections and sudden temperature changes.
- Swim bladder disorders even seem to happen spontaneously in healthy fish, and it’s common for other fish in the tank to remain unaffected.
How do you treat a swim bladder disorder?
- Executing a reliable treatment is challenging for your saltwater fish since the exact cause of the disease is not known.
- Try treating the tank with an antibiotic remedy. This treatment should help if the cause is an infection.
- Try raising the temperature to 80 degrees Fahrenheit (27 C), and then don’t feed the fish for three days. Sometimes low water temperature can slow the digestive process, which puts undue pressure on the swim bladder.
You can also make your fish more comfortable by lowering the water level, which lets it move around easier. Unfortunately, if the sick fish isn’t getting better and is unable to eat, it might have to be put down to avoid needless suffering.
#12. Physical damage from another fish
Symptoms:
- Damage to the body or mouth. Open wounds.
- Split or damaged fins. Loss of scales but with normal coloration.
- Loss of an eye as fish commonly attack another individual’s eyes.
What causes physical damage?
- The most common cause is an aggressive fish that attacks its tank mates.
- Fish can also be hurt when tangled in a net or not handled carefully.
How do you treat physical damage?
- Put injured saltwater fish into a separate tank and treat them with an antibacterial. Give them plenty of time to heal fully.
- You must discover the cause of the damage. Observe your fish until you can find which one is attacking the others. You don’t want to fix an injured saltwater fish only to put it back into the same environment!
Do you need additional help with your saltwater fish?
If so, then I recommend purchasing the above book as a resource. It will go into more detail about each of the diseases and illnesses we discussed today, along with MANY more!
Here is how you can prevent almost every saltwater fish disease!
I’m not sure if you noticed, but basically, every illness and ailment listed above is caused by the same few things.
If you missed it, here is what you need to do to make sure your saltwater fish stay healthy.
- Quarantine new fish for a few weeks before adding them to an existing tank.
- Test your water every week to look for issues. You must maintain excellent water quality to keep diseases away. If there are any imbalances, you need to address them immediately.
- Do not overcrowd your tank! Too many fish causes stress and too much waste, which then causes illness.
- Perform a 25% partial water change every two weeks. Clean the gravel as well to remove excess waste.
- Don’t overfeed your fish. Only feed them what they can eat within a few minutes.
Have you experienced any other saltwater fish diseases or illnesses?
Please share what happened below!
