The Beginner Guide To Saltwater Fish Disease

Updated 2024

Disclaimer: I am NOT an expert.  I am NOT a veterinarian.  I am NOT a medical professional.  But I have spent years trying my best to compile the most accurate information available.  Saltwater hobbyist rarely agree on anything, especially when it comes to fish disease diagnosis and treatment.  Please use this guide as a starting point for your research.

Navigating the world of saltwater fish diseases is like embarking on a challenging underwater expedition. There’s an abundance of blogs and online communities delving into every aspect of this subject. However, what seems to be missing is a comprehensive guide that brings all these puzzle pieces together into an easily digestible format. And guess what? This guide is here to step up to the plate!

Diving into the realm of fish diseases? Be prepared, because it’s like swimming against a strong current:

  • Regardless of your efforts, fish may still face health troubles.
  • By the time you identify an issue with your fish, it’s often too late.
  • Certain species respond positively to specific treatments, while others swim in the opposite direction.
  • Medications can disrupt your beneficial bacteria and other tank inhabitants.
  • Before gaining experience, distinguishing between normal and abnormal behavior is like trying to spot a seahorse in a sandstorm.
  • Many diseases showcase similar symptoms, but demand tailored treatments.

I think you get the point.

The two best things you can do to prevent disease is to use a quarantine tank.

Dive right into the guide and don’t hesitate to share your insights or point out any inaccuracies. Reach out to me at

Craving an in-depth fish disease guide? Take a plunge into the book recommended below, authored by Edward Noga. Regarded as the fish disease bible, it could become your ultimate aquatic companion.

A blue book cover with yellow writing titled Fish Disease

I) Why Saltwater Fish Get Sick

1. Stress

You know, it’s kind of like us humans – stress isn’t our best friend, right? Well, fish feel that too. Stress isn’t their swim buddy either. Just like there’s always that neighbor who keeps popping up, diseases are sort of like the uninvited guests in your tank. But here’s the cool part: if your fish is a tough cookie, it can totally give those diseases a run for their money and stay the picture of health.

2. Aggressive Tank Mates

So, let’s chat about “The Beginner’s Guide To Saltwater Fish” options. They’re like the friendly bunch in the neighborhood – all about the community vibe. Now, don’t get me wrong, there are a couple of things to keep in mind. You know how some folks just can’t resist a bit of drama? Well, aggressive fish are like that. They might give their tank mates a hard time, nipping at fins and causing all sorts of trouble – tears, scrapes, and stress galore. And guess what? This fishy drama can actually weaken immune systems and pave the way for diseases to sneak in.

3. Water Parameters

When it comes to fish disease, there are a couple of troublemakers to watch out for – wonky water conditions, for starters. Think high levels of ammonia and nitrate – those are like red flags waving at fish health. Also, if your tank’s feeling too much like a sauna or an ice bath, or if the saltiness is playing hide-and-seek, it’s not good news either.

Now, picture this: you know how we humans don’t really enjoy rollercoaster rides in our lives? Well, fish aren’t fans of that in their tanks either. They’re champs at adapting to their surroundings, but too many changes can really throw them off their game and leave them feeling like they’re stuck in a never-ending aquarium adventure.

4. Injury

When a fish ends up with scrapes and cuts, it’s like leaving the door open for trouble. These little injuries make them way more susceptible to getting hit with a follow-up bacterial, viral, or fungal infection.

5. Tank Size

Fish, just like us, have their own preferences when it comes to living arrangements. It’s a bit like finding the perfect apartment for each of them. For instance, if you decide to squeeze more than a couple of clownfish into a 20-gallon tank, be prepared for a potential clash of personalities. And, let’s not forget about the pufferfish – trying to house one in a 40-gallon setup might not have a happy ending. So, the key is making sure your tank matches the right size tag for your aquatic buddies.

6. Overstocking

Alright, let’s dive into a tank-sizing topic. Now, there’s no one-size-fits-all rule when it comes to how many fish you can have in there. But here’s the deal: there’s a tipping point where things can get a tad overcrowded. And when that happens, brace yourself for potential fishy disagreements and a struggle to keep that tank’s natural balance in check.

7. Age

Just like us humans, fish tend to become more susceptible to diseases as they near the end of their life journey.

8. There Is Always Disease In A Tank

Even with all the careful quarantining in the world, there’s a truth you can’t dodge – some diseases and pesky parasites might still find their way into your tank. You see, your tank is like a microcosm of life, and some bacteria are just part of the package. However, here’s the twist: if a fish is stressed or nursing an injury, it’s like opening the door for those diseases to take center stage.

II) How To Prevent Fish Disease

Let’s talk about a secret weapon – the quarantine tank. Now, I get it, not everyone’s on the quarantine train. But hey, don’t follow the crowd! A quarantine tank isn’t a one-size-fits-all solution, but it’s like having a detective’s magnifying glass. It gives you the chance to keep an eye on your fish for any potential issues and treat them without causing chaos in your main tank. So, remember, it’s okay to be the cool fish keeper who’s all about that QT life!

2. Dips

Let’s break it down: there are two power moves in the fish world – medicated dips and freshwater dips.

Now, if setting up a quarantine zone isn’t your thing, no worries! You’ve still got a trick up your sleeve – the two-part Blue Life Safety Stop. It’s not a miracle cure, but think of it as your fish’s personal spa treatment. It can wave goodbye to parasites, bacterial hitchhikers, and even those pesky fungal infections. It’s like a refresh button for your fishy pals!

3. Keep Stable Water Parameters

Nailing this mission is totally doable. Just keep a close watch by testing often, give your filters some regular TLC, throw in those weekly or biweekly water changes, and, hey, consider adding a temperature controller like the Inkbird to your toolkit. It’s all about being the master of your tank’s destiny!

4. Remove Aggressive Fish

It’s pretty normal for fish to be a bit nosy when newbies move in. But if the constant snooping doesn’t calm down within a day or two, it might be time to give the instigator a timeout.

Now, aggression isn’t just a one-time act – it can surprise you anytime. Let me share a tale from my office tank: I had these two clownfish coexisting in my 20-gallon tank for ages. Then, out of nowhere, the female fish decided she was the boss and started bossing the male around. Talk about a power trip! So, I had to make the call and move her to the grand 120-gallon arena. It’s like life’s never short on drama in the fish tank world!

5. Drip Acclimate All New Fish

If you’re hungry for step-by-step guidance on drip acclimation, be sure to dive into The Beginners Guide To Saltwater Fish.

Here’s the game plan: start slow by letting your bags float to match the temperature. Then, kick things up a notch with a drip acclimation session to balance out those water parameters. It’s like giving your fish a VIP welcome to their new home – less stress and a better chance to fend off any sneaky diseases that might try to crash the party.

Innovative Marine Accudrip Acclimator For Drip Acclimation

6. Don't Overstock

This one’s crystal clear – better to play it safe and have a few fish than to overcrowd the tank.

7. Add Fish Slowly

Here’s the deal: don’t rush out and grab a bunch of fish in one go, then plop them into your tank pronto. Take it easy. Loading up your tank with too many fish at once can send your water chemistry on a rollercoaster ride, and your trusty biological filter might get overwhelmed.

If you’re dreaming of a tank with, say, ten fish, start small – introduce a couple first, then build up from there. It’s like crafting your own aquatic masterpiece, one fish at a time.

8. Buy Community Fish

When it comes to fish vibes, they often fall into three cliques: peaceful, semi-aggressive, and downright aggressive. If you’re just getting your feet wet, it’s a wise move to steer clear of the aggressive fish squad.

If you’re curious about the best picks, don’t miss The Beginner’s Guide To Saltwater Fish – we’ve got the top ten lined up for you!

III) Signs & Symptoms Of A Sick Fish

Wrapping your head around this can be a bit of a puzzle. See, until you’ve got some real hang-time with each saltwater fish species, gauging what’s normal is like trying to find a seahorse in a sandstorm. So, don’t hesitate to dive into online forums or swing by your local fish store (LFS) for some fishy wisdom.

Now, picture this: all the signs and symptoms listed below can be like little red flags that your fish might be under the weather. But hey, remember, it’s all about context. Think of it like reading between the fishy lines. For instance, a fish turning its nose up at dinner might not be feeling down – it might just be a foodie with a particular taste!

1. Loss of Appetite

Fish have their own dining styles. Some are chill grazers, nibbling away throughout the day, while others are like speedy food warriors, pouncing on anything edible that comes their way. Understanding the munching preferences of each of your fish is key.

But here’s the deal: no matter the dining vibe, if you spot a sudden shift in your fish’s eating habits, it might be a sign that something’s amiss. Trust your fishy instincts!

2. Flashing

Ever witnessed fish doing a lightning-speed rock rub? That’s what we call flashing – when they zip themselves against the rocks in a hurry. It’s like their way of saying, “Whoa, gotta shake off this pesky infection or parasite!” This impromptu dance might be their tactic to ditch unwanted guests. However, here’s the twist: all that energetic rubbing can lead to scratches and openings, making them more vulnerable to extra infections. It’s like a double-edged sword in the underwater arena!

3. Bulging Eye

Picture this: it’s like the fish’s eye is on a mission to break free from its body and make a bold appearance. This phenomenon, where the eye seems to bulge out, is quite the sight. While it’s more commonly seen in the freshwater fish world, it’s still a curious marvel in the underwater realm.

4. White Dots

Spotting white dots on a fish’s skin, often as small as grains of sand, is like waving a red flag. It’s a signal that something’s up – it could be a case of Marine Ich or Velvet, and trust me, neither of those are welcome guests in the fish tank party.

5. Red Gills

Frequently, swift breathing and reddened gills go hand in hand. These indicators often point to the presence of a bacterial or parasitic infection, signaling that your fish might be in a bit of a health pickle.

6. Rapid Breathing

Pinpointing this issue can be a bit of a puzzle, especially if you’re not familiar with the usual behavior of each of your fish species.

7. Hiding

Certain fish have a knack for being the masters of hide-and-seek, while others are like the stars of the open water, zipping around freely. Keep an eye out for any shifts in their behavior – it’s like reading their underwater story.

8. Cotton Looking White Growths

Frequently, this could point to a potential fungal or viral infection brewing.

9. Cloudy Eyes

It’s possible that an internal bacterial infection might be at play here.

10. Frayed/Disintegrated Fins

It could either indicate fish aggression or a potential disease issue.

11. Missing Scales Or Red Growths

Once more, it could either be a reflection of fish aggression or a potential disease concern.

12. Lethargy

Important to know the baseline for each of your fish to diagnose this symptom appropriately.  Some fish are just naturally lethargic!

IV) Four Types Of Fish Disease

Right around the corner, in section V) of this guide, you’ll find an in-depth exploration of the most prevalent fish diseases and their treatments. Brace yourself for some insightful discussions! Now, as for the diseases themselves, they’re divided into four distinct categories. Get ready to dive into the details!

1. Bacterial

Infections caused by bacteria can take on different forms: they might be internal, external, or even show up on the surface. Now, here’s where it gets a bit technical – bacterial infections can be split into Gram-positive or Gram-negative types. If that sounds like a foreign language, don’t worry! We’ve got a detailed breakdown waiting for you in section V. Oh, and if you’re hungry for a comprehensive explanation and a lineup of antibiotics, The Beginner Guide To Saltwater Fish Medication & Treatment is your go-to resource. One more thing to note: bacterial infections often sneak in as secondary troubles, tagging along after your fish is already facing some health challenges.

2. Fungal

Skipping the “plant or animal” category, fungi are a unique bunch – they’re spore-making beings that include molds, yeasts, and mushrooms. Now, onto the main act – the most typical saltwater aquarium fungus often shows up as a white, fluffy, cotton-like patch on fish. While it’s not exactly a frequent guest in this hobby, it’s worth keeping an eye out for this unusual visitor.

3. Parasitic

Champion of the “common and dangerous” category, parasites take the lead. They’re like the ultimate freeloaders – setting up shop in or on another organism and having a feast on their host’s dime. In the saltwater world, big shots like Marine Ich, Velvet, and Flukes make the scene as classic examples. They’re the bad guys to watch out for!

4. Viral

Taking a step back from the spotlight of parasites and bacterial infections, viruses step in – although they’re not as frequent visitors. Here’s the twist: when it comes to viruses, there’s no magic cure in the medical cabinet. While bacteria are these single-celled characters, viruses are like miniature stealth operatives. They can’t go solo – they need a host to survive. And boy, are they tiny compared to bacteria! Viruses are masterminds at hijacking cells and reprogramming them to churn out new viruses. It’s like they’re running their own secret viral production line!

V) Common Saltwater Fish Diseases & Treatments

Disclaimer: I must reiterate the following points for emphasis – I am not an authority in this field, I am not a veterinarian, and I am not a medical practitioner. However, I have dedicated considerable time to gather the most precise information at my disposal. It’s worth noting that consensus within the saltwater hobbyist community is a rarity, particularly regarding fish disease identification and treatment. I kindly advise using this guide as a preliminary resource to initiate your research journey.

Parasitic Diseases

a pictograph of the life cycle of marine ich. From a cartoon clownfish on the top center that is clearly infected with white spots, ich detaches from the fish body, settles in the sand and reproduces, then finds a fish host to complete the cycle
© Bulk Reef Supply
      • Common Name(s):** White Spot Disease, Saltwater Ick
      • Scientific Name:* Cryptocaryon Irritans
      • Description: Among the most prevalent saltwater fish diseases, Marine Ich is a familiar foe. It’s occasionally mistaken for Marine Velvet, a far more sinister ailment. Marine Ich infiltrates the skin and gills of fish, with many healthy individuals mounting a defense. Often characterized by small, salt-sized white spots, this disease may primarily affect gills, showing no outward signs. Its extended life cycle poses a challenge for complete tank eradication.
      • Symptoms: White spots on fins, gills, and body.
      • Treatments: Copper Power stands out as the prevailing and effective treatment. The Tank Transfer Method also boasts high efficacy. A freshwater dip can temporarily eliminate external parasites, offering limited respite without a definitive cure. Employing a UV sterilizer aids in eradicating the free-floating parasite phase. A few hobbyists have reported favorable results using a combination of Ruby Reef Rally and Ruby Reef Kick Ick.
      • Our Recommendation: Opt for either a quarantine tank strategy employing Copper Power or embrace the Tank Transfer Method for tackling Marine Ich.

2) Marine Velvet

close up of a live brown fish head with what appear to be tiny gold spots all over the body. This fish has a common saltwater infection known as marine velvet.
By Mydigitalife - Own work, CC0,
      • Common Name(s): Marine Velvet, Gold Dust Disease
      • Scientific Name: Amyloodinium Ocellatum
      • Description: Sharing a similar life cycle with marine ich, Marine Velvet, however, stands as a far more perilous adversary. It frequently displays symptoms akin to ich, causing a perplexing challenge in distinguishing between the two parasitic infections.
      • Symptoms: Distinctly smaller and rounder white dots in contrast to ich. These dots envelop the entire fish. By comparison, marine ich presents as larger and oval-shaped.
      • Treatments: The available treatments for Marine Velvet are limited to Copper Power and a freshwater dip – no more, no less. Regrettably, once Marine Velvet is diagnosed, the outlook is often grim, and affected fish frequently do not survive.
      • Our Recommendation: For a potential chance at combating Marine Velvet, Copper Power becomes a pivotal option (when confined to a quarantine tank), and a freshwater dip might provide temporary relief from symptoms.

3) Flukes

© Humblefish, December 4th, 2015.
      • Common Name(s): Gill Flukes, Skin Flukes, Marine Flukes
      • Scientific Name: Three common families in saltwater: Ancyrocephaladae, Gyrodactylidae, & Capsalidae.
      • Description: Flukes, parasitic flatworms, are tissue feeders that target fish’s external surfaces and gills. These small, nearly transparent organisms are elusive to detect. Placing them in a freshwater dip will prompt them to detach and become opaque. Flukes reproduce rapidly, with the newly hatched free-swimming offspring readily seeking new hosts.
      • Symptoms: Symptoms include rapid breathing, frayed fins, loss of appetite, head twitching, discolored blotches on fish, flashing, and white translucent spots that resemble ich.
      • Treatments: Commence with a freshwater dip to eliminate external flukes, followed by the application of an antiparasitic treatment.
      • Our Recommendation: If the infestation is severe, initiate with a freshwater dip to eliminate external worms and provide relief to your fish. Subsequently, administer Hikari PraziPro for more comprehensive treatment.

4) Clownfish Disease

© Humblefish, May 8th, 2016.
      • Common Name(s): Anemonefish Disease, Brook
      • Scientific Name: Brooklynella Hostilis
      • Description: While anemonefish, particularly clownfish, are notorious targets of brooklynella, other fish species can also fall prey to it. This ailment’s presentation often resembles marine velvet and frequently initiates its attack on the gills. Its life cycle remains entirely within or on the host, without a separate cyst stage. Due to its rapid lethality, swift intervention becomes pivotal.
      • Symptoms: Symptoms encompass swift breathing, flashing, decreased appetite, and lethargy. Advanced stages may manifest as skin shedding. Similar to marine velvet, but accompanied by higher slime production.
      • Treatments: Formaldehyde, frequently available under the trade name formalin, serves as a common treatment option.
      • Our Recommendation: Ruby Reef Rally incorporates formalin. While we’ve experienced success with it, it’s important to note that treatment duration might span several weeks rather than days. Follow the directions closely for the best chance at success

5) Black Spot Disease

© Humblefish, August 4th, 2016.
      • Common Name(s): Black Ich, Tang Disease
      • Scientific Name: Turbellarian Flatworms
      • Description: These appear as small black dots blanketing the skin, which are actually flatworms. In comparison to marine ich or marine velvet, black ich poses much less of a threat. Its life cycle mirrors that of ich and velvet, progressing through active infestation, detachment into the substrate for reproduction, and culminating in a free-swimming stage seeking new hosts.
      • Symptoms: Observable symptoms include black spots roughly the size of a grain of salt, flashing behavior, lethargy, and loss of appetite.
      • Treatments: Treatment options encompass praziquantel, hyposalinity, and formalin. Freshwater dips can offer temporary respite as well.
      • Our Recommendation: For tackling black ich, we suggest leaning toward Hikari PraziPro as the primary option. If the infestation is substantial, consider complementing it with a freshwater dip for a more comprehensive approach.

6) Uronema

© Humblefish, May 8th, 2016.
      • Common Name(s): Uronema
      • Scientific Name: Uronema Marinum
      • Description: While often found on Chromis, Uronema can potentially affect any fish species. Identifying Uronema can be challenging because it doesn’t rely on a host to survive. Consequently, if this organism is present in your tank, the only surefire way to eradicate it is by breaking down the tank and implementing sterilization measures.
      • Symptoms: Notable symptoms include the emergence of red sores.
      • Treatments: Utilizing formalin as the initial step, followed by a course of antibiotics spanning several weeks to counteract potential secondary infections, stands as the recommended treatment.
      • Our Recommendation: Ruby Reef Rally for primary treatment. Once Uronema is eradicated, administer a two-week regimen of Seachem Metroplex and Seachem Focus to mitigate the risk of secondary infections.

Bacterial Infections

The realm of bacterial infections is diverse, yielding a multitude of variants. Nonetheless, they tend to exhibit comparable symptoms. Frequently, they emerge as secondary infections following a parasitic episode. These infections can manifest either internally, externally, or both.

The complexity with bacterial infections lies in their accurate identification. Distinct bacterial strains necessitate distinct antibiotics for effective treatment.

      • Cause: Typically ensues after a parasitic infection or arises due to compromised water quality.
      • Symptoms: Notable symptoms encompass frayed or deteriorating fins (referred to as fin/tail rot), visible open sores, abdominal bloating, protruding eye(s) (known as popeye), clouded eye(s), and the emergence of white cotton-like growths around the mouth, fins, or body.
      • Treatments: Employing a UV sterilizer can aid in eliminating free-floating bacteria, while targeted antibiotic treatment is crucial for addressing the bacterial issue.
      • Our Recommendation: For tailored treatment, delve into our Beginner Guide To Saltwater Fish Medication & Treatment to select the appropriate antibiotic based on the specific disease symptoms.

Fungal Infections

While relatively uncommon in the saltwater aquarium hobby, fungal infections can surface when a fish is under stress. Similar to bacteria, fungus likely resides in your aquarium at all times, yet a robust and healthy fish can typically repel its advances.

© My First Fish Tank, 2019
      • Cause: Typically arises subsequent to a decline in water quality and stress experienced by the fish.
      • Symptoms: Manifesting as white, cotton-like fuzzy growths on or within the mouth, fins, and body of fish.
      • Treatments: Available treatments include Kordon Malachite Green, API Pimafix/Melafix combination, Kordon Methylene Blue, and Seachem Kanaplex/Focus combination.
      • Our Recommendation: Begin by executing a substantial water change (ranging from 25-50%). Scrutinize and enhance your water parameters as needed. Maintain close observation of your fish’s condition. If all else proves ineffective, opt for the most suitable medication option from the aforementioned choices, taking into account whether it will be applied in your display tank or quarantine tank. Delve deeper into the specifics of each medication through the insights provided in the Beginner Guide To Saltwater Fish Medication & Treatment.

Viral Infections

The prevailing virus among saltwater fish is known as lymphocystis. This virus materializes as a distinctive white growth, resembling a cauliflower or small pebbles, often akin to warts. As of now, no effective antiviral treatments are available. Thus, maintaining pristine water conditions and safeguarding fish from stress are your primary strategies. Lymphocystis can often be benign and typically resolves independently over time.

© Chris Grondahl,
      • Name: Lymphocystis
      • Cause: Primarily triggered by deteriorating water quality and fish stress.
      • Symptoms: Distinguished by the presence of white growths resembling cauliflower, as well as white pebble-like formations on the exterior of the fish’s body. These growths might also take on a wart-like appearance.
      • Treatments: Regrettably, there are no established antiviral treatments available.
      • Our Recommendation: Enhance your water quality by implementing a substantial water change, ranging from 25% to 50%. Rigorously assess your water parameters and enhance them as needed. Mitigate stressors by eliminating aggressive fish or any other potential stress sources from the tank. Lymphocystis growths are typically benign and tend to resolve autonomously over time.

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