Learn the Truth About Constipated Goldfish

a cupcake with a cat on top of it.

One of the internets favorite fish “diagnoses” is a “constipated goldfish.” What is “constipation?” It is the inability to pass fecal material usually due to dehydration or lack of fiber in the diet. Thankfully, goldfish are physiologically built to never be constipated.

Freshwater fish physiology prevents constipated goldfish

Why is my goldfish NOT constipated? Imagine a goldfish swimming in their tank. Remember, goldfish are freshwater fish. Now, the next part might require you to pull out your high school chemistry notes or ask your child to explain the following concepts. Goldfish live in a hypoosmotic environment, whereas they are more dense than their surrounding water. Through osmosis, water is constantly moving into a goldfish to create equilibrium, essentially super-saturating a fish’s tissues.

Now, since fish don’t resemble giant gelatinous blobs, a freshwater fish’s kidneys and gills work hard to remove the additional water. Freshwater fish produce copious amounts of dilute urine and try to avoid drinking water. (This is the opposite for marine fish). This is why, when a fish has issues with their kidney or gill function, they swell up like a balloon, creating the “pinecone”-like, commonly referred to as “dropsy.

So, if a goldfish is super hydrated, having dry fecal balls does not fit. Their gastrointestinal tract is super lubed and will not produce compacted fecal balls. Therefore, your goldfish is NOT constipated. We also commonly see concern about “long stringy white poop.” This is simply the mucosal lining of a bowel movement. Your goldfish’s feces is coated with mucus to make it slide easier, just like yours.

If your goldfish is acting lethargic and depressed, check your water quality. This is the #1 cause our office sees for sick fish. Poor water quality causes your fish to become stressed out and will reduce their immune function.

But doesn’t fiber fix “constipated goldfish?”

But what about that dietary fiber? Have you ever looked at your goldfish’s diet? Here are some of the most common goldfish diets available on the market next to their fiber:

  • Aqueon Goldfish Granules – 5.0% (5g per 100g)
  • Hikari Goldfish Gold – 3.0%
  • API Goldfish Pellets – 5.4%
  • Fluval Goldfish Pellets – 4%
  • Omega One Goldfish – 3%

Now, you know those “shelled green peas” that are the cure-all of the “constipated” goldfish. They have 5% fiber, the EXACT SAME as all of these fish foods. Feeding a constipated goldfish more fiber actually doesn’t do much, since goldfish metabolism isn’t robust enough to process lots of fiber.

Here are how “magic” green peas work (condensed from our article):

  • Sinking diet = no more floating goldfish
    • Phyostomous fish (i.e. goldfish) have duct between esophagus and swim bladder
    • Eat a surface = floating upside down
    • Goldfish = golden retriever
  • Low protein = less ammonia = better water quality
  • You get the exact same result from keeping your tank clean and feeding a sinking diet
    • Or with sinking fish, a floating diet
  • Your fish does not have “swim bladder

One thing to remember, is that goldfish, like all other fish, are ectotherms. Water temperature directly dictates their metabolism. In cold water, fish are not able to digest their diet. Usually, this is the case in outdoor ponds. Indoor tanks in homes with poor insulation can also be at risk for low metabolism. Usually, fish will self regulate and not eat when it is too cold.

However, some goldfish, with some of the same traits as your golden retriever, will eat and eat and eat until they explode. If the water isn’t warm enough and they can’t digest, the food will sit around and rot inside their intestines. Is this the same as “constipation?” Of course not! Follow our feeding instructions for outdoor ponds, insulate your tank or get your fish a heater so they can properly digest their food.

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12 thoughts on “Learn the Truth About Constipated Goldfish”

  1. Pingback: White Stringy Poop in Fish - Aquatic Veterinary Services

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  3. So my two goldfish are ALWAYS carrying long string poops.. one site says constipation and one says NOT constipation. How can I tell what is going on with them? When i had them in my basement they did not do that, but now they are upstairs they are..should i try putting them back downstairs where its actually colder?

    1. a woman in a lab coat smiling for the camera.
      Dr. Jessie Sanders

      Temperature can certainly change how fast a fish’s metabolism moves. A faster moving metabolism is more prone to producing fecal casts with no food (long, white poop). If you are concerned about your fish, please contact your local aquatic veterinarian https://fishvets.org

  4. Please help, my 19 year old fantail goldfish “Jacques “ is bloated, sitting on the bottom of the tank and not feeding.
    All water quality it good
    Jacques has never been sick before, i am desperate to help him

  5. Joselle Monarchi

    We have an outdoor pond with many goldfish. A few in particular look blown up like balloons. They are acting normal, swimming normally and eating just fine. What possible could be the matter with them and can we get them looking normal again?

  6. Pingback: Betta Fish Poop & Constipation: Everything You Need to Know - Fish Life Today

  7. Pingback: Betta Fish Poop & Irregular Bowel Movements: Every Little Thing You Required to Know - LaoKoon Aquarium

  8. So i dont know if its been answered but my gold fish seems to have an extended/protruding anus like its 2-4mm long and same colour as scales, eats and poos normaly ive got the water set to a day night cycle with high temp at 28-31 itry to keep the ph level but its a new tank, it had seeds along bottom on one side for plant growth but it ate it all. Im not sure where else to look for answers, can you help??

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