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Dropsy in Fish; Swollen Betta, Kidney Infection
DROPSY in fish; prevention, causes, and possible treatment of this malady that is often a symptom of other problems.
By Carl Strohmeyer
This article originated from a forum post that I responded to where the owner of a female betta fish was attempting to treat this often un-treatable malady.
The fish keeper noted that she (the female Betta) seemed buoyant and the swollen cavity appears to be filled by either air, or a clear liquid, when she swims in front of the lights.
The fish owner was also instructed to use Maracyn (Erythromycin), which is generally a poor choice for Dropsy since the main treatable cause is Aeromonas bacteria and Aeromonas is a gram negative bacterium so the use of Erythromycin is generally useless.
Aeromonas Infections in Fish
My suggestion would be to use Kanamycin in both the tank AND in a medicated bath at double normal dose (for 30 minutes)
*Use of Kanamycin, Kanaplex in Aquariums, Ponds
*Medicated Fish Baths
What is Dropsy?
Dropsy is generally a symptom of something else other than the classic and more noticeable symptoms that are then labeled as "Dropsy".
Most often Dropsy is Kidney related, which results in swelling and fluid retention due to poor kidney function results in the classic "pinecone" look of fish sick with Dropsy.
Poor osmoregulation is usually the second most common cause, and in more rare instances digestive, and maybe liver malfunction/infections.
The loss of ability for osmo-regulation of electrolytes is often a contributing cause, which is another reason for correct positive mineral ion and trace element levels.
Please see these two articles:
*Aquarium Chemistry; Calcium, Electrolytes, GH, KH, & more
*Do Fish Drink; Proper Osmotic Function .
Generally due to the cause or area of infection (or organ failure), Dropsy can often be very difficult to treat, especially if caught in an advanced case in the fish.
What the aquarist often observes is a “pinecone” swelling generally caused by fluid building inside the body cavity (often involving the Kidneys), for this reason, reducing this swelling is an important step in effecting a cure.
I have heard of Minocycline also being recommended for this (although it can be effective). I do not recommend this as Minocycline has been shown to cause serious damage to the kidneys, which is the last thing you want to do to a fish suffering from Dropsy or even suspected of this malady.
Information on Minocycline:
Use of Minocycline, Maracyn 2 for fish treatment
I would also note that since Aeromonas bacteria is a common cause of infections that result in Dropsy and since this bacterium is often anaerobic; maintaining good circulation, aeration and overall good tank hygiene goes a long ways in treatment and even further for prevention (since Dropsy is difficult to treat and cure).
Please read more about optimum tank conditions in the prevention section further into this article, as I have been able to prevent Dropsy much more successfully (as per controlled tests) than actually treat a full blown case of Dropsy!.
Sometimes liver issues are blamed for Dropsy, which is certainly possible, however liver malfunction and infections generally do not result in the classic "pinecone" Dropsy appearance, rather the fish may bloat slightly and almost always results in loss of color, loss of appetite, and the fish tends to hide more.
One of the functions of the liver is to remove toxins and this is why the symptoms I describe are more prevalent with liver issues.
This said, besides treatment for a possible underlying infection, you want to take steps to remove the swelling.
Here are the steps I would take (these apply to ALL fish, not just Bettas):
- Change water! (25% should be fine)
- Perform a medicated bath with Methylene Blue and a Sulfa based drug OR Kanamycin.
To prepare this bath I use 1 teaspoon 2.303% solution per 5 gallons (double dose) in a bath of aquarium water from the tank the fish you wish to treat came from, I usually use about a ½ gallon of water, however you may use less. Measurement of the Methylene Blue does not need to be precise as this bath should be used for about 30 minutes.
Make sure you keep the water in a warm area, as in a cold room the water temperature can drop rapidly which would stress the fish.
As to the Kanamycin or Sulfa Based Drugs (such as Triple Sulfa or Maracyn Plus), I generally have used twice the recommended in tank strength in these baths of Kanamycin.
Keep in mind that Kanamycin, while not as toxic to kidneys as Minocycline, it is still toxic, yet is also very effective for infections of the kidneys! The point being is use with caution and do not use in the main aquarium, only in baths when fish have Dropsy so as to keep the exposure time low but effective (hence the double strength treatment in the short duration of a bath).
Recommended product links/references:
*Kordon Methylene Blue
I STRONGLY recommend the use of salts in this bath as well at about double the normally used tank strength; 1-2 teaspoons sodium chloride (regular salt) per gallon and 1/8 to ¼ teaspoon Epsom salt per gallon of bath water.
Do NOT pour this water back into your display aquarium when finished!
This can be performed twice per day.
For further information (more in depth) about fish baths, please read this article:
Fish Baths/Dips for supplemental (& even primary) treatment of Bacterial infections
- Add one tablespoon of regular salt (sodium chloride) per 5 gallons of aquarium/tank water.
Add a Wonder Shell or similar product to add needed calcium and mineral cations.
What these minerals will do is add electrolytes and change (and improve) the osmotic balance of the fish vs. the surrounding water to hopefully pull fluids thru the body thus reducing swelling.
For more about electrolytes, please read this article: Aquarium Chemistry; Why calcium and electrolytes are important
- Treat tank water with Kanamycin (Kanaplex), or possibly with Neomycin or Nalidixic Acid.
Also consider feeding the infected fish with fish food soaked in Neomycin such as Neoplex along with in tank treatment of Kanamycin (hospital tank is best).
Other treatments of note are Minocycline (Maracyn II) and Metronidazole (SeaChem makes an excellent pure Metronidazole).
Additional recommended product links/references:
*SeaChem Neoplex (Neomycin)
Sometimes a “cocktail” approach with more than one medication is necessary for Dropsy, such as Kanacyn and Metronidazole or Neomycin together (and this still includes the baths!!).
Please note that combining Metronidazole with Neomycin does not improve results, so this "cocktail" combination should ONLY be with Kanamyacin with EITHER Neomycin or Metronidazole!
Here is more info about aquarium medications:
AQUARIUM MEDICATIONS; treatments, how they work, and which ones to use and not to use
The Aeromonas bacteria (that is often present in healthy aquariums) can cause infections that will manifest this way in poor water conditions, especially in aquariums with poor circulation and high amounts of DOC (dissolved organic compounds) along with a high "Bio-Load" as Aeromonas Bacteria can be anaerobic and thrive in low oxygen, high dissolved organics conditions.
Please also reference: Bio load in Aquariums
So maintaining a healthy aquarium with regular water changes, good filtration (if possible, as this is why I see more cases of Dropsy in Betta kept in a bowl), good feeding practices (not over feeding and using quality foods), and maintaining proper water parameters (ammonia and nitrites 0, kH 50+ ppm, GH 100+ ppm, nitrates under 40 ppm).
A water parameter that is often missed (as the more obvious ammonia and nitrites are usually noticed) is proper calcium and electrolytes (positive mineral cations).
If RO is used (or drinking water that is nothing more than RO water with a few minerals added for “taste”), there are usually insufficient electrolytes and calcium for proper osmotic function and fluid retention can result, which will then lead to kidney infections.
Please read these articles for more about this aspect of fish care:
*Proper Osmotic Function; Use of RO Water
* AQUARIUM CHEMISTRY; The importance of Calcium, GH, KH, Magnesium to Fish
All this goes a long way in prevention of Dropsy and other diseases, especially when poor osmoregulation is the direct cause or even indirect cause of Dropsy.
By indirect I mean opportunistic infections getting a foothold internally in your fish due to poor levels mineral cations & buffers present in your aquarium water.
A proper diet makes a large difference here.
Do not feed your fish "meat based" proteins. I recommend aquatic based proteins such as white fish meal, shrimp or even the proteins found in spirulina algae.
As a basic Betta diet I recommend Sanyu or Hikari Betta Gold pelleted foods.
There are many other quality Betta foods as well, although I do not recommend flake foods for bettas as their staple diet.
However Flake Food such as Spirulina based Spirulina 20 are excellent when used as a "fish food slurry/soak" for frozen or freeze dried brine shrimp, worms or other carnivorous diet food that Bettas prefer
For other fish, Spirulina 20 is an excellent staple diet that can and should be combined with other foods to provide complete nutritional variation.
Poor quality proteins (or better; unusable amino acids for fish) can lead to digestive problems or Renal failure, which CAN lead to the symptoms of Dropsy.
All proteins are made up of amino acids, some are usable (by fish), and some are not.
Those that are not are disposed of by kidneys in the fish. This can lead to renal failure or infection.
This is where highly digestible foods such as Spirulina algae come in.
Also always soak all dry foods in water for 5 minutes prior to feeding as this will remove air that can lead to infections of the digestive tract (this is best for ALL fish, goldfish in particular).
For more information about proper nutrition, see this article:
"Fish Nutrition; What ingredients are needed for proper fish growth and health".
See also this section: Fish Nutrition; FD/Frozen Foods Spirulina Slurry
Other suggested reading:
Spirulina Algae; The Aquatic Health Benefits for Tropical, Marine and Goldfish.
Fish Food Recommendations, product links:
*Spirulina 20 Fish Flake Food
*Sanyu Betta Gold
*Hikari Betta Bio-Gold
*Hikari Spirulina Enhanced Brine Shrimp
The above is a VERY short list of quality, highly digestible fish food diets, so please read the article I suggested earlier about Fish Nutrition!!
To summarize prevention; I have seen very few cases of Dropsy in the literally 1000s of aquariums I have maintained in regular contracts over the years.
HOWEVER, I have seen MANY cases of Dropsy when non service customers call me out to see why their fish are sick and I often will observe very poor water conditions feeding practices, etc.
The reason is simple for my regular contract customers success, I have always maintained my tanks with regular cleanings, proper electrolyte levels, a balanced Redox, proper fish nutrition, and often UV Sterilization.
Highly Suggested Further Reading:
* “Aquarium Disease Prevention”
In controlled test/studies, the incidence of Dropsy was almost non-existent where all points outlined in the above Disease Prevention article were followed!!
*Aquarium Redox Potential
*UV Sterilization, Sterilizer Use; The importance in fish disease prevention
*Freshwater Aquarium Care Basics & Information
*Aquarium Filtration Information
*Fish Anatomy For further help in understanding the anatomy of fish (so as to know where the Kidneys are located), please read this article.
*Planaria & Detritus Worms in Aquarium