Goldfish and Dropsy: Bloating Disease, How It Works, And How to Treat It

by Adam Till

A Note Of Warning About Goldfish Disease and The World "Wild" Web

First off, I'm very sorry that you're having trouble with your goldfish.

There is an awful lot of conflicting information on the web, and most if it is because of websites repeating information from other websites without having direct experience with treating disease themselves. Usually this is best recognized by the lack of original photographs of the disease processes, and a lack of references to claims made in the article or treatments suggested.

Please be careful treating your fish using such information, and always contact an aquatic veterinarian for assistance whenever possible.

Since I am just a breeder and not a vet I cannot legally diagnose or prescribe a course of treatment for your fish, so instead I will simply offer a description of what I do when I encounter these issues.

(cover image) Simba, one of our highest producing ranchu sires,
suffered from severe dropsy that he eventually recovered from

Dropsy is normally recognized by most people when their goldfish start to swell up with retained fluid.

In its extreme form, the goldfish will start to "pinecone", or balloon in size to the point where the scales on the fish start to project outwards like the plates of a pinecone.

Picea Pungens Young Cones
Goldfish whose scales start to project outwards
from dropsy bloating start to resemble
pinecones like these

Normal Prognosis From Dropsy in Goldfish

Poor to guarded.

Most goldfish that come down with dropsy to the degree where it is recognized by the average fish owner are advanced enough that the overall prognosis tends to be poor.

Sometimes treatment can be successful if the fish is treated appropriately. Dropsy isn't usually contagious to other fish in most cases.

Useful To Have On-Hand To Treat Dropsy

How Do You Recognize Dropsy in Goldfish?

Ideally, the best time to recognize dropsy is when the fish stops behaving the way it normally does in any fashion. I have an entire article available on assessing "not quite right" with goldfish, and that's a good one to read when it comes to initial stage dropsy.

Not all fish that seem a little off end up developing dropsy, but most cases of dropsy I've dealt with start out in subtle ways.

In it's most extreme and most easily recognizable state, dropsied fish seem to balloon up to large size almost like puffer fish, and that causes their scales to stand out from their sides in a very abnormal fashion.

This is usually called "pineconing" as a result, and anyone that's had the misfortune of seeing a fish in this condition knows it's an appropriate description.

Above is the video clip from which our cover photo was taken, showing Simba in a sad and bloated state. Not a happy goldfish for sure!

What Is Dropsy in Goldfish?

Dropsy in goldfish is the accumulation of excess fluid inside your fish which it cannot expel by normal action of the kidneys and other internal organs. Dropsy itself is an old term for edema, which is a swelling of the soft tissues due to excess fluid.

The excess fluid causes the tissues of the fish to swell, and also to build up in the body cavities themselves eventually causing the "pineconing" effect described earlier. 

Also worth noting is that dropsy itself isn't  a disease, but a symptom of a disease (a bodily dysfunction). That might seem like it's splitting hairs, but it's not.

The varying treatments suggested by people and websites can sometimes be traced to poor information, but also to the fact that dropsy can have many causes.

These can include:

  • Parasitic causes
  • bacterial causes
  • kidney dysfunction
  • harmful aquarium products (like some algaecides)
  • a sudden drop in water temperature after heavy feeding (causing intestinal blockage)

...and many others.

In people, a simple example of edema would the generally harmless swelling of your legs and feet after a long airplane or car trip caused by lack of circulation and movement. In extremes, congestive heart failure can cause extreme edema (or dropsy) as well.

Likewise, in goldfish minor disease processes that are easily resolved can cause minor swelling of the tissues, and something like complete  kidney failure can cause massive dropsy swelling.


Zhao's fancies oranda showing distention of body due to fluid accumulation, also known as dropsy

 Viewing your fish from above can really help to determine if they're bloated. Try to do this once in a while when they're healthy so you have a frame of reference.

 Chronic vs One-Time

Depending on the cause and whether it can ever be fully resolved, dropsy at times can be either one-time or chronic (repeated).

Internal infections that resolve with medication, egg binding in females that can't lay eggs for some reason in one season, or intestinal blockage that's resolved with a better feeding program are generally one-time occurrences.

Tumours, kidney wasting, and environmental problems that are seasonal may cause chronic issues that rear their heads repeatedly.

If multiple fish are affected, this is more likely to indicate that the problem isn't a dysfunction within a single fish like a tumour, but instead has an outside (and possibly transmittable or environmental) cause.

Stress As A Cause

One of the more regularly encountered causes of dropsy is internal infection as a result of bacterial overgrowth, and often when the bacteria are cultured by a vet or lab the bacteria are found to be varieties which are commonly found in the environment.

Since these bacteria are generally harmless or in concentrations too low to cause issues, one simple explanation of why they may become a problem at certain times is stress. Like with people, stress will depress a fish's immune system, and prevent it from functioning properly.

Things that can stress a goldfish include:

  • irregular lighting patterns or cycles
  • lack of hiding places
  • lack of social contact
  • poor quality, badly stored, or expired foods
  • poor water quality
  • over stimulation (too much commotion, kids banging on glass etc)
  • breeding season


Bottom sitting, like with Sephina the oranda above, is a BAD sign. Unfortunately she never recovered from dropsy.

 Some symptoms of a stressed fish include:

  • Lack of energy
  • Bottom sitting
  • Loss of appetite
  • Changes in color that seem abnormal (all goldfish change color to some degree as they age)
  • Tumors or growths
  • Inflammation
  • Flashing 
  • Clamped fins
  • Gasping at the surface

How Do I Treat Dropsy in Goldfish?

Following on from the description above, how I most effectively treat dropsy in my fish will depend on what's wrong with them in the first place.

Whenever I first notice that one of my fish isn't acting quite right, for example:

  • not coming up for food as eagerly as normal
  • sitting on the bottom for long periods not moving (but also not asleep)
  • clamping fins and/or not swimming properly
  • not trailing at least some poop at least some point in the day

...the first thing I do is to isolate the fish in a separate tank.

Isolating your sick fish in a quarantine tank is the easiest way to assess their health 

That's not because dropsy is contagious (in and of itself it isn't, though whatever is causing it might be), but because I want to be sure that the goldfish is able to eat and poop normally.

Set Up The Hospital Tank or Tub

If you haven't had a chance to do a water change for a while, or don't have a test kit to test for proper water parameters, fill the hospital tank with water from the main tank (and top up the main tank with fresh water). You should use the main tank water so you aren't shocking the sick fish by moving it straight into a tank with fresh, clean water.

Ironically, moving a fish straight from dirty water into clean can be just as dangerous as clean to dirty if the fish has had a number of months to adapt to the dirty conditions. This is especially important for fish that are already potentially sick.

Although a lot of sources will get you to try to adjust your water chemistry to some theoretical ideal of pH or hardness, personally I believe that this is not only stressful on the fish, it's also hard on you. You'll never be able to exactly duplicate water conditions batch to batch, and constantly having to adapt to new water is adding extra load onto an already stressed fish.

Additionally, if massive changes are required to make your water "perfect" by some combination of chemicals or arcane rituals, you're less likely to change water due to cost or time constraints. Better to work with your local tap water when at all possible, and to keep your life easy and your fish's world consistent.

Zhao's fancies oranda showing signs of dropy. She passed a few days later

Bottom sitting is a bad sign. Goldfish need to move to properly help food move through their intestines.

Set Up The Sponge Filter

Sponge filters are simple and inexpensive to keep around for hospital use. 

The bubbles keep the tank water well oxygenated, the filter creates very little current to knock a sick fish around, and there are no sharp edges or intakes to damage sick fish that may not be swimming in a controlled fashion.

Usually I keep an extra hospital sponge filter in a display tank at all times so it stays cycled with good bacteria, but even stored dry it's still a good choice for a hospital tank.

Check for Constipation

One of the other more common reasons for dropsy to develop seems to be constipation in goldfish, or the inability to expel poop normally.

When that happens, the undigested food will back up in the goldfish's simple digestive tract, and either will start to ferment or create conditions where bacteria multiply too readily.

It's my feeling that reducing these bacterial levels (along with the waste gas they produce) is why anti-bacterial treatment options like kanamycin work on occasion when treating some cases of dropsy (though lacking any lab equipment other than a microscope this is just a guess at this point).

By moving the fish into isolation, and especially with a bare bottom hospital tank with a sponge filter, it becomes very simple to see and assess poop either on the tank bottom or glued to the sponge filter.

If My Goldfish Will Eat...

Ideally, I isolate the fish BEFORE it stops eating. Goldfish that won't eat are dramatically less likely to recover in my experience.

 Simba never stopped eating entirely, but had dramatically reduced appetite at times. That's NOT normal for a ranchu!

If the goldfish is fed a small amount (roughly dime sized) of one of the soft foods mentioned at the start of this article, they should be producing poop of roughly the same color (or normal brown) that same day.

The soft, easily digestible food is a FAR better choice for a sick fish than pellets or flakes would be, since they're easily able to pass and digest them.

If you alternate days with green Repashy Super Gold with a white steamed egg mix (don't add the green spirulina when you make it), you should even see different colored poop each day, which can be helpful as a visual aid.

On that note, if you use the egg mix, don't freak out if the poop is white. In this case it doesn't indicate parasites, but rather just the color of the digested egg.

If My Goldfish Isn't Producing Poop...

 No waste is a bad sign

In cases where my goldfish isn't producing visible waste, I personally immediately go to epsom salts dosed at 1 teaspoon per gallon of tank water.

The use of epsom salt has both a laxative effect on the intestine (helps clear constipation) and increases the output of the kidneys (helping to clear fluid buildup).

For cases of dropsy I avoid the use of more strongly concentrated dip treatments, and instead focus on more gentle but longer duration bath treatments like described above.

Strong dip treatments work well for eliminating external parasites or the like, but risk being a bit too much stress on fish suffering from organ issues.

If The Goldfish Is Producing Poop...

Here, I instead use aquarium salt (sodium salt), now dosed at 1 tablespoon per gallon.

This is to ease any breathing difficulties that can accompany the swelling of dropsy, and to ease pressure on the kidneys (to lessen the osmotic pressure).

Freshwater fish like goldfish have to continually use energy to maintain their internal chemistry as the surrounding water continually tries to dilute nomral body salts by osmosis.

This takes energy, and when the fish is under stress adding salt to the water will reduce the amount of energy used to overcome osmosis.

In All Cases, I Treat Dropsy In Goldfish With Kanaplex

Personally, since our hatchery runs daily automatic water changes and I'm not overly concerned about the risk of dirty water having caused dropsy, I immediately dose the hospital tank with Kanaplex per the label.

In every case where I've had success, Kanaplex was involved.

Kanaplex by Seachem

It's not a guarantee of success by any stretch, and the sooner the medicine is added the better things seem to turn out, but around here we have no issues using medicine appropriately and promptly.

If water quality might be an issue in your case, there's a small argument to be made for just cleaning up the water and seeing if the fish recovers.

Even in cases where the cause of your dropsy might be parasitic in nature, I'd advise caution (and would probably seek medical advise) before trying to administer a dewormer like praziquantel (PraziPro, Amazon or Aquarium CoOp) to an already sick fish.

The added metabolic load from dying parasites may be more than your fish's internal organs can process if its already showing signs of dropsy.

A Note On Pharmaceutical vs Natural Remedies

 Although there are a number of "natural" remedies around that claim to help with dropsy or other issues, there hasn't been enough research (or even dedicated, logical study with successful outcomes) of their use to warrant my recommending any at this point.

The use of pharmaceutical drugs (used appropriately and preferably under the supervision of a vet) does have a history of helping issues like this however, and I personally find the cost of the medicine combined with the proven track record well worth the life of my animals.

Water Changes and Redosing Kanaplex

I've had most success doing large water changes between each dose of Kanaplex.

As a result, I tend to do 100% water changes to help make sure that water quality stays as close to perfect as possible.

To do the changes, I gather up the water change siphon I keep dedicated for hospital use only, 2 dedicated 5 gallon Lowe's buckets, and a jug of vinegar.

I rinse everything quickly with straight vinegar, then gather my bottle of Seachem Prime dechlorinator and take the Kanaplex medicine out of the fridge where it's stored.

I start the siphon draining water out of the hospital tank into one of the buckets, and then once the bucket is half full, switch to the second bucket and fill it to the same level.

Once the buckets are filled, I carefully lift the fish by hand into one of the buckets. Doing so by hand rather than using a net not only reduces trauma to the fish, but lets me assess how "slimy" the fish is at the time. Increased slime coat production is often a sign of disease or irritation, and so a history of knowing what a normal fish feels like lets me use this as a helpful tool for health assessment when they're not feeling normal.

I'm extra careful with severely swollen fish, since it's reasonable to assume that they'll be feeling particularly sensitive when bloated to that degree.

The second bucket is used to contain the sponge filter, which can be safely disconnected for the short time it takes to drain and refill the main tank.

With the filter and fish removed, the rest of the tank can be siphoned clean. I make note of how much (if any) poop has been passed, and if I'm alternating foods the color change helps show whether the gut is emptying each day properly.

When the tank is completely empty, it can be refilled completely from the tap. I make sure to match temperature to what the old tank temp was to avoid temp issues.

When the tank is filled, dechlorinated and salted, the filter can be squeezed out in the bucket, added back into the main tank, the goldfish released back into the tank with a little bit of food, and the old water disposed off (ideally in the garden).

A Note About Temperature

Somewhat bizarrely, a number of references to treating dropsy seem to indicate raising the temperature of the tank to up to 86F "to combat bacterial infections".

Given that increasing temperatures within the healthy range for goldfish actually PROMOTES bacterial growth (here's a reference for healthy bacteria growth rates) there's no logical reason that I've found to elevate temperature above your normal, room-type temps.

Temperatures above 83F are known to depress goldfish metabolism, for example, and can only help to stress sick goldfish further.

If your normal room temperatures are at these elevated levels already then there's no need to cool the tank (again, think minimizing stress), but I wouldn't recommend heating the tanks to this level for sick fish. Not only do water changes become more complicated, but you might be causing your fish more stress than necessary.

If I Notice Improvement In the Goldfish

 Simba finally starting to perk up, with much reduced bloating. On the mend!

Once I notice improvement in the fish, be it something like:

  • less pronounced pineconing or swelling
  • increased appetite
  • less clamped fins

...or something similar, or after I reach the label-recommended three doses over six days, I stop use of the medication.

As soon as the fish is expelling waste properly, I switch from 1 teaspoon per gallon magnesium salt to 1 tablespoon per gallon aquarium (sodium) salt.

I keep doing the water changes every 2 days or so until the fish has recovered, until it passes away, or until we decide to put the fish down.

Feeding in Hospital Tanks

Goldfish digestive systems are designed to have small amounts of food multiple times a day. The food coming in the front end ideally helps to move the waste out the other end.

Likewise, in order to help repair internal damage and restore proper organ function as soon as possible, one of the critical components to providing the energy for this repair effort is consistent, high quality food.

That said, keep in mind your water quality for quarantine tanks; especially since they tend to be on the small side.

Particularly if you don't have a cycled, pre-prepared spare filter to convert ammonia waste to nitrate, you can end up causing extra harm to the fish with too much food in that it causes the fish to expel too much waste.

Without water changes to handle the waste, you can end up causing secondary issues that hinder healing from the dropsy issues.

Again though, every time you change water, you need to remedicate the tank.

It's a bit of a fine balance to get right, and another argument for keeping a spare filter going in your main tank.

Post Recovery Care

If your goldfish happens to pass away, first off, I'm very sorry!

Hopefully you end up with a happy result, however, and eventually the fish can be reintroduced into the main tank again.

Once the fish is healthy, the amount of salt can be slowly reduced down to normal levels (ie 0 additonal salt) again. Rather than doing 100% changes to accomplish that, a series of two or three 25-50% changes will dilute the salt back down to reasonable levels over time.

After an extra water change and cleanup on the main tank to reduce waste levels there, the formerly sick goldfish can be added back into the main tank.

Although I usually end up watching the fish like a paranoid parent anyway, I try to make an extra effort for the next few weeks to observe the fish, and make sure symptoms don't reoccur.

Hospital Tank Cleanup

The best way I've found to stand down the hospital tank is to completely rinse it out, scrub it down with vinegar, and leave it to completely dry out.

This will eliminate most potential pathogens, and since dropsy is rarely caused by something contagious, I feel comfortable with this method. Bleach could be used as a final rinse by the extra paranoid.

I usually give the sponge filter a thorough rinse, soak it in vinegar overnight, and return it to the main tank to "reseed". The vinegar rinse will sterilize it from most harmful agents, but it will also destroy the filter bacteria that lived on the sponge.

Rinse the buckets and siphon in vinegar as well, bundle them, and put them away dry.

Time Is Of The Essence With Dropsy

One final note to point out is that the sooner you do something to figure out whether your goldfish is okay or just having an off day, the better.

Anytime we've lost fish I can usually track it down to getting a "funny feeling" from a fish about 2 days before things really get bad, but shrugging it off as something that's not worth worrying about yet.

Can that make you crazy as a pet owner? Yes. I wish it wasn't the case, but that's the reality with fish that can't really communicate issues to you as easily as other pets might.

How Do You Prevent Dropsy in Goldfish?

 Regular, large water changes help to keep goldfish healthy

Since the causes of dropsy are numerous and hard to define, advice for how to prevent dropsy in the first place is equally challenging to compile. Good advice would be to: 

  • start with clean fish. Find healthy sources of goldfish, and treat every new purchase with a good deworming medicine
  • keep  tank water clean of excess waste. Don't neglect water changes, and keep waste level to 0ppm ammonia, 0ppm nitrite, 40ppm nitrate max 
  • keep bacteria levels moderate. This is almost impossible to measure, but can be helped by removing excess fish waste manually if not consumed by plants or snails
  • feed foods that don't slow digestion too much. Too much pelleted or flake food can constipate goldfish, and when digestion takes too long bacteria levels can build up
  • learn your fish's natural behaviours. Look for anything out of the ordinary, and isolate fish that cause you to "get a funny feeling" about how they're acting

Good luck, and I hope you never need to make use of this article!

Adam Till
Adam Till


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