11 of the Most Common Saltwater Fish Diseases (AND HOW TO CURE THEM!)

Have you ever wondered if your fish are sick? Fish can also get infected with diseases! It can be one of the most problematic issues when owning a saltwater aquarium. Saltwater fish diseases are problematic and several are considered tank wipers in our hobby.

Today’s post isn’t to scare you, but to educate you on the common diseases that afflict marine fish. The most common diseases are due to parasites that they may carry within and outside their bodies, causing issues such as infection or inflammation. I’ll walk you through all the common fish diseases and provide ways to cure them. Let’s get started!

Most Common Saltwater Fish Diseases

These are some of the most common diseases that are seen in saltwater fish.

1. Saltwater Ich (Marine White Spot Disease)

Saltwater Ich
Ich

Ich’s version is saltwater tanks is Cryptocaryon irritans vs Ichthyophthirius multifiliis – it’s freshwater version. It is considered a moderately serious parasite that infects fish. Ich is one of those parasites that you can either choose to eliminate entirely or manage.

For those that decide to manage it, you focus on having a low stress environment for your fish and managing with equipment like UV sterilizers, Ozone, Diatom filters, or an Oxydator.

Fighting Marine Ich is all about know it’s life cycle. The picture below from Charles Raabe posted on Humblefish’s website is a good illustration of how the cycle works.

Saltwater Ich Life Cycle

Symptoms of Saltwater Ich

  • Salt-like white spots on fish usually on the fins or body
  • White spots are spread out and can be counted. Too many to count would indicate a far more serious disease (Velvet)
  • Flashing, scratching, twitching, and heavy breathing

Treatment of Saltwater Ich

  • Fallow period (fishless) is 76 days
  • Copper like Copper Power
  • Chloroquine Phosphate in quarantine system
  • Hyposalinity in fish only or quarantine systems
  • Manage with equipment like UV Sterilizers

2. Marine Velvet

Marine velvet is the most common of what I call the deadly 3. The deadly 3 are 3 of the most serious diseases in the saltwater hobby that have the potential of wiping out all the fish inhabitants of your tank. It is a disease that is not to be taken light, sometimes killing fish before symptoms show.

This disease requires a 76 day fallow period to eliminate and cannot be managed like Ich. You have to wipe it out completely. This disease is the #1 reason to quarantine your saltwater fish.

Symptoms of Marine Velvet

  • Number white spots – so many that you can’t count. Almost dust like
  • Flashing, scratching, twitching, and heavy breathing
  • Fish sensitive to light
  • Fish swimming to current to breathe
  • Mysterious sudden deaths of inhabitants

Treatment of Marine Velvet

  • Copper like Copper Power
  • Chloroquine Phosphate
  • Fallow period – 76 days
  • Disease must be treated in a quarantine tank to fully eliminate

3. Brooklynella (Clownfish Disease)

Brooklynella

Brooklynella is the 2nd most common of the deadly 3 saltwater fish diseases. It typically affects clownfish, which is how it got its name clownfish disease from. Other fish can be inflected, but their physical symptoms will look different as you will see white blotches versus white film.

This disease has the potential to wipe out all the fish in a saltwater aquarium. Like with velvet, you can only eliminate it by doing a quarantine and doing a fishless period (fallow) for 6 weeks.

The medication used here are powerful. Formalin is the old school way of bathing and is no longer available in several states. Chloroquine Phosphate is the drug of choice here, but also difficult to obtain.

Symptoms of Clownfish Disease

  • Powderly white film
  • Almost web-like white film on fish in advanced stages
  • Large white blotches on non-clownfish
  • Sudden deaths with any physical symptoms

Treatment of Clownfish Disease

  • Formalin bath (if legal in your state) – Ruby Reef Rally can be used as an option.
  • Formalin bath – 45 minutes
  • If Ruby Reef Tally – 90 minutes
  • Freshwater dips can be used if above meds are not available. Bathe for 5 minutes
  • After bath – treat with Metro + Chloroquine Phosphate
  • Seachem Metro for 14 days in aquarium and feed to fish with focus binding if fish is eating
  • Chloroquine Phosphate
  • Fallow period – 6 weeks

4. Uroema marinum

Uroema is the scariest and hardest to battle of the deadly 3. This parasite has a direct life cycle, which means it has no encrusted stage like Brook. While this may mean the parasite is easier to eliminate, that is not the case. This disease can live without a host, mainly feeding on detritus to maintain itself when fish aren’t available.

You simply cannot get rid of this disease once it’s in your aquarium. It is that much of a nightmare. You can manage after you get rid of fish with sympthoms by maintaining a very clean saltwater aquarium and not purchasing chromis fish – the pathogens favorite host.

This is the only disease of the deadly three where euthanasia is recommended. Once the red sores appears, it’s usually too late to help the fish. Medication used here are strong just like Brook and velvet. Do not take this disease lightly

Symptoms of Uroema marinum

  • Red sores on fish
  • Sores appear in a vertical line usually around the center of the fish
  • Sudden death without physical symptoms

Treatment of Uroema marinum

  • If no sores are present – Formalin or Rally bath to start
  • If sores are present – Use freshwater dip. Also okay to use if medications are not available
  • Cholorquine Phophate
  • Seachem metro treated food with focus to treat internal infections
  • Euthanasia with clove oil

5. Flukes

Flukes are a hidden parasite that you will often come across with large fish like Tangs. While not serious on their own, it is common for these flukes to cause secondary infections (usually bacterial infections) on the infected sites.

This is one of the few diseases on the list that you can treat for in a display tank using Prazipro or General Cure. You can also use a freshwater dip to provide relief to the fish, as long in this video by Meredith Presley.

Symptoms of Flukes

  • Lethargic fish
  • Flashing, scratching, twitching, and heavy breathing

Treatment of Flukes

  • 5 minutes freshwater dip for immediate relief
  • Prazipro or API general cure to treat 5-7 days, perform water change, then another 5-7 days
  • Hyposalinity for 7 days

6. Black Ich

Black Ich

Black ich is parasitic flat worm that usually affects Tangs (picture source). Like flukes it is a moderately severe disease that can develop secondary infections. It has the same treatment as flukes and can be treated in the display tank

Symptoms of Black Ich

  • Small black spots on body
  • Spots are raised

Treatment of Black Ich

  • 5 minutes freshwater dip for immediate relief
  • Prazipro or API general cure to treat 5-7 days, perform water change, then another 5-7 days
  • Hyposalinity for 7 days

7. Bacterial Infections

Saltwater Bacterial Infections

Bacterial infections are very serious in the saltwater hobby. There are two types – gram-positive and gram-negative. Gram-negative are more serious and unfortunately the most common with saltwater fish. These infections are typically secondary infections from aliments like Ich or flukes. Wounds will also cause infections.

Treating a bacterial infection requires antibiotics and a quarantine tank. Because there are so many different types of bacterial infections, multiple medications are used. Board spectrum medications are the best to use to get a handle on the infection.

Because you cannot differentiate between a gram-positive or gram-negative infection without a scrape and microscope, it’s best to assume all bacterial infections you come across are gram-negative.

If untreated, a bacterial infection will typically kill a fish. Most gram-negative infections will kill a fish within 1-2 days.

Symptoms of Bacterial Infections

  • Redness, soreness on body
  • White film or fungus looking growths
  • Cloudy eyes
  • Fin & tail rot

Treatment of Bacterial Infections

  • 90 minute dip in Ruby Reef Rally (one of the active ingredients is an antiseptic)
  • Antibiotic options
    • API Triple Sulfa
    • Seachem Sulfaplex + Neoplex
    • Spectrogram (only available via American Aquarium)
  • Treat antibiotics for 7-10 days

8. Head & Lateral Line Erosion (HLLE)

HLLE in Tang

HLLE is a condition that is typically associated with tangs (picture source). There isn’t a definitive answer as to why this condition occurs, but there are several theroies:

  • Poor nutrition
  • Stray voltage
  • Carbon
  • Stress

Since there this isn’t a disease but more of a condition, this can be treated without medication. Tackle this by addressing all possible causes. Feed your fish quality frozen food and greens like Nori for tangs. Use a ground probing to remove any stray voltage and get any carbon in your filter/sump out of your system.

HLLE will sometimes heal over time, other times the fish will have some scarring from the condition. It’s all dependent on how quickly you can address the issue.

Symptoms of HLLE

  • Discoloration of fish
  • Looks like color is peeling off from fish
  • White or grey fading of color in patches

Treatment of HLLE

  • Increase nutrition with quality frozen food and vitamins like Selcon
  • Remove any stray voltage with a grounding probe
  • Remove any carbon from your filter or sump
  • If fish was treated with copper – increase nutrition condition may heal over time

9. Internal Infections & Parasites

Internal infections can either be worms, parasites, or bacterial infections. Since it’s difficult to tell what your fish has, it’s best to tackle this ailment with a broad medication. General cure + focus is the big practice here with Metro + Prazipro being another combo (General Cure has both).

This is a very common issue with imported fish, but also easy to cure if you catch it early. This is a condition that can be treated in a display tank, though best handled in a quarantine tank before the fish is introduced to the display system.

Symptoms of Internal Infections and Parasites

  • Sunken bullies (like video)
  • White stringy feces
  • Skinny fish that can never gain weight

Treatment of Internal Infections and Parasites

  • General cure + Focus mixed with food
  • Treat for 10-14 days or until feces is no longer white for several days

10. Swim Bladder Disease

Swim bladder disease is an all too common issue with imported deep water fish. Wrasses in particular are the most common fish affected by this aliment due to poor handling by the importer.

I’ve personally dealt with this issue several times in my reefing journey. I got so frustrated with this from imported fish, I stopped buying wrasses online unless it was a what you see is what you (WYSIWYG) get wrasse.

You can do the 3 treatments below in the bullet points. Some cases get to the point where you will need to lance the fish to remove the gas bubble. This is an advanced techique that should not be attempted by a beginner.

If you are going to attempt the lancing method (see video above), try to get an experienced reefing member from a reef club or considering calling your local vet. Some vets have performed the procedure with large ornamental fish or koi.

Fish will usually die without treatment as they cannot compete for food and will be subject to bullying. I haven’t seen any swim bladder wheelchairs made for saltwater fish versus goldfish (where these devices are more common).

Symptoms of Swim Bladder Disease

  • Fish is unable to swim upright
  • Fish unable to swim downwards
  • Gas bubble present in belly

Treatment of Swim Bladder Disease

  • Epsom salt – one tablespoon per 5 gallons
  • 30 minute Methylene Blue bath
  • Metro + Neomycin + Focus in food
  • Lancing (See video) do not attempt unless with an experienced reef or have a license vet perform it

11. Lymphocystis

Lymphocystis on Clownfish

Symptoms of Lymphocystis

Lymphocystis makes this list as it is confused by ich. The disease fortunately is rarely fatal. However, the bad new is this is a viral infection. The fish will continue to carry the virus for the rest of its life. It can be managed.

The healthier the fish is, the more likely this virus will stay in remission. Focus on putting your fish in a low stress environment with a great diet. The virus will come and go, but the your fish can live a healthy life carrying it.

  • White color growth on fins and back of fish
  • Starts small, then grows in size

Treatment of Lymphocystis

  • There is no known cure
  • Can put virus in remission by providing a low stress environment and high quality diet

How to prevent Many health issues in your fish

Prevention is the best medication when it comes to disease. There are many things that you can do at home to help prevent many of these issues in your fish. Your favorite pet’s health depends on water quality, diet and levels of stress; however there is still more we could do for them! Here’s how:

1. Quarantine New Fish

This is your #1 preventative measure against diseases. Many saltwater fish are imported, which means they go through a lot of stress to get to your home. This stress lowers the fish’s immune system and makes them venerable to disease. Some importing practices are also not ideal, leading to several issues after getting the fish.

You can save yourself a lot of headache and tank crashes by quarantining. If you want to learn more about it, I have a great article on quarantining.

Not interested in quarantining fish? If so, consider working with an online retailer who specializes in quarantined or pre conditioned fish. My top two choices for these would be Live Aquaria’s Drivers Den or TSM Corals. Go with TSM Corals if you can fish the fish you want there – they have the best practices in the industry.

2. Provide A Quality Diet

To keep your fish healthy, it is important that they have a proper diet. A well balanced and species appropriate food will not only make them full but also less likely to fight with other individuals in the tank over meals! Top quality frozen food is the best food you can purchase for saltwater fish. You can also do cultivated live food like black worms, but I’m assuming many readers here don’t want to go that route.

For frozen food, there are two brands I highly recommend. LRS and Rod’s Food are the two best frozen food makers on the market. Both are difficult to find online, but you can find them at specialty fish stores.

3. Provide Pristine Water (Avoid Poor Water Quality)

Part of establishing a low stress environment for fish is providing quality water. For saltwater tanks, an aquarium sump is the best filter you can purchase. Use a sump to your advantage by installing quality equipment like protein skimmers too keep your tank filtered and consider getting an auto top-off unit to keep your salinity stable.

Saltwater tanks are different than freshwater tanks in that some may not need a traditional water changing schedule. Test your water quality with quality test kits and only change water to maintain your parameters. If you have a reef tank, consider investing in a dosing pump to keep your calcium, alkalinity, and magnesium levels up

4. Reduce Stress

There are a few ways to reduce stress. I explained water as one. The other would be shelther and tankmates.

For shelter, you can provide your fish with lots of rocks. A large amount of live rock and/or dry rock provides plenty of spaces for fish to get shelter in. For most reef tank setups, shelter will usually not be an issue.

Tank mates are the next. You want compatible tank mates. Too many territorial disputes and bullying from aggressive fish will lead to stress, injuries, and disease. Add your most passive fish first and your most aggressive last.

5. Purchase Captive Bred Fish

Captive bred fish are generally healthier and have a better time adjusting to a home aquarium environment. You can avoid a few of the aliments on this list like Swim bladder disease from purchasing tank bred fish. You will still come across Marine Velvet and other serious diseases, but you will lower your risk in getting outbreaks with healthier fish who are used to living in a captive environment.

Creating A Medicine Cabinet

Anyone who has multiple saltwater fish and tanks eventually deals with sick fish. Whether you quarantine or not, it’s a good idea to keep medication on hand for emergencies! Here are some common medications that can help – I’ve added them together in one table so they’re easy to read. Most are available online or at your local fish store. Purchase them now before you are in a bind. Many medications on this list have long shelf lives.

TypeMedications
Parasitic (External)Copper Power, Prazipro, Ruby Reef Rally, Chloroquine Phosphate
Parasitic (Internal)General Cure, Seachem Metroplex, SeaChem Focus (To Bind)
FungalAPI Fungal Cure
BacterialAPI Triple Sulfa, Seachem Sulfaplex, Seachem Neoplex

FAQS

What diseases can saltwater fish get

The most common diseases saltwater fish can get are ich, marine velvet, internal parasites, and flukes.

How do you identify a saltwater fish disease?

Most saltwater fish disease have the same symptoms. Look for symptoms like labored breathing, flashing, scratching, white dots or film, sores, and discoloration.

There are also deadly disease that may kill a fish before symptoms show. Any sudden unexplained death of a fish should be question as it could be related to a deadly disease like Marine Velvet, Uroema, or Brook.

What Does Ich look like on a marine fish?

Saltwater ich looks like small white dots on the fish’s body or fins. Ich spots are not numerous. You should be able to count them when observing at the fish. If you cannot count them, this could be marine velvet. If the dots grow in size, this is likely Lymphocystis.

What does a diseased fish look like

A disease fish will show one of the following characteristics: discoloration, white spots, red sores, scratching, flashing, and labored breathing. Physical symptoms are a sign the condition has become serious. Action should be taken ASAP to help the fish.

What is killing my saltwater fish?

Sudden deaths are worrisome in a saltwater fish tank. Unexplained deaths are likely a result of the 3 deadly marine diseases – Marine Velvet, Brook, or Uroema. If this is a fish that is a quarantine tank that suddently dies, it could also be a result of transplant shock. If your fish dies in quarantine, empty and sterilize and tank. Let the tank dry for 24 hours before attempting to quarantine another fish.

Further Resources

It would be unfair for me to talk about saltwater fish diseases without mentioning Dr. Fish himself, Humblefish. His forum is the go to if you are dealing with sick or infected fish in the saltwater tank hobby. Give his forum a visit if you need immediate assistance. The community there is amazing. They can be a lifesaver in a hobby where Vets are hard to find with experience in these aquatic animals.

Final Thoughts

Saltwater fish diseases tend to be more serious then with freshwater fish. Because of this, quarantining is the best practice. If you come across a sick fish, take action right away. Use this guide to help identify what you are going against. If you have any questions, leave them in the comments below. Thanks for reading!

by Mark

Mark is the founder of Aquarium Store Depot. He started in the aquarium hobby at the age of 11 and along the way worked at local fish stores. He has kept freshwater tanks, ponds, and reef tanks for over 25 years. His site was created to share his knowledge and unique teaching style on a larger scale. He has worked on making aquarium and pond keeping approachable. Mark has been featured in two books about aquarium keeping - both best sellers on Amazon. Each year, he continues to help his readers and clients with knowledge, professional builds, and troubleshooting.

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