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.