Stringy White Fish Poop: Normal or Sick Fish?

normal fish poop

Alright, we’ve cleared up the internet’s favorite fish diagnoses: swim bladder, dropsy, constipation and mystical green peas, but what about that “white, stringy fish poop?” Somehow, many internet diagnoses involve this mysterious phenomenon in fish and have linked it to internal parasites. Well, let us set the record straight…

White, stringy fish poop is a poop with no food in it.

A small fish swimming near rocks.
Fish with normal poop

Welcome to Your Fishes’ Digestive System

Most gastrointestinal systems work very similarly, fish, humans and other pets included. The gut is responsible for absorbing nutrients and getting rid of wastes and undigestible material. In order to help move things along, our guts are lined with mucus-producing cells to help things slide through. Without this lubrication, you’d never be able to pass a single poop, swell up and die. Fish have the exact same cells in their guts! And although freshwater fish cannot become constipated (sorry, but we’ve already been over this – you’ll have to take your complaints up with osmosis), they still need a little extra help moving things towards the exit.

Most of the time, you’ll barely notice this mucus coating because of what your fish eats. The mucus is stretched thin and you’ll see a mush similar in color to the pellets you feed. If your fish has not been eating, you will only see the mucus. This is the “stringy, white fish poop” in fish. Is this a sign of disease? Not really, it only means your fish hasn’t eaten. This may only be a few hours or a few days. Many fish, especially tropical fish, are used to foraging throughout the day. If they’re only fed a few times a day, some of the fecal movements may have food, others may not. And this is normal!

Across the ornamental fish industry, there is a wide variety of feeding styles and diets. From strict herbivores, to herbivorous-leaning omnivores, true omnivores, carnivore-leaning omnivores and strict carnivores, you can learn a lot about a fish from the diet they eat. What they eat dictates where they live, the temperatures they require and how their digestive system operates.

Horrific Consequences of Fasting Fish

A lot of those internet diagnosticians will recommend fasting fish when they are sick, which isn’t a good idea. When fish are sick, they need nutrients to swim and run their immune system. Yes, some diseases may require limiting food, but that decision is for your veterinarian, not “helpful” strangers on the internet. As an aquatic veterinarian, I have very rarely recommended dietary cutbacks and have NEVER recommended holding food.

How can I tell if poop is really a parasite?

Yes, the “white fish poop” does look a lot like an internal parasite. But unless your fish have come into contact with any wild-caught fish, invertebrates or unsanitized décor items, the chance of them getting an internal parasite is slim to none. In the 10+ years we have been in business, seeing over 1,000 clients, we have diagnosed it three times. All of these cases involved wild-caught fish. The biggest different between an empty fecal cast and a parasite is that one is alive and the other is not.

If your fish’s poop decides to get up and dance, preferably against the current, you may have something to worry about. Since they are so light and easily pushed around by water flow, some fecal casts can give the appearance of movement, but watch them closely. If necessary, pull it out of your tank using a turkey baster and put it in a clear glass or cup. In the still water, it will be easier to tell if it can move on its own. If it’s still swimming, despite being in a cup of calm water, that would be a parasite.

So, let’s put the “stringy white poop” clinical sign away. Yes, it is a clear indication your fish is not eating, but you should know that already if you watch them during feeding time. There is no medication we can give you to get rid of it, and it is a NORMAL function of your fishes’ digestion. And never withhold food unless directed by your aquatic veterinarian.

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41 thoughts on “Stringy White Fish Poop: Normal or Sick Fish?”

  1. Jessie,
    Great post. I see those from time to time. I had heard something that vaguely indicated it was a problem sign, but wasn’t sure. I’m glad to hear that if seen occasionally it’s probably nothing to get too worried about. Happy Fish Keeping,

  2. Patrick eggleton

    If your black molly is pregnant and having white stringy poo could that mean she’s almost ready to give birth

  3. Currently treating my betta for bloating however her housemate in a tank of ten has been sinking from the rear tail. Please help

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  5. This is so helpful, thank you. I’ve been squinting at my guppys’ poop for far too long trying to decide whether I should be worried and honestly I didn’t think I should be based on how the fish are acting (normal, healthy, active, very very interested in the brine shrimp I just fed them) but when seemingly the entire internet is yelling “that means parasites” it was hard to relax.

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  7. Frances Applequist

    One of my fish (a year-old platy) died in a terrible, almost sci-fi–horror, way. When I found him, something like a long white string extended from his belly and wrapped around the air hose at least five times. If this was an intestine, I don’t know how it attached to the hose in the first place. It looks like the poor creature struggled and swam in circles around the hose, pulling it’s insides out until it died.

    I have had fish tanks for over thirty years and NEVER saw anything like this. I’m not even sure I’m going to be believed.

  8. I have a new Betta that did a clear / white poop with a brown dot on the end. I posted on Betta fish groups and they said it’s worms. I wondered if it’s in fact the mucus mentioned in this article. I wonder if I could possibly send a photo for advice, I’m in Australia so can’t visit with my fish 🙂

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

      Yes, this applies to marine fishes as well. They are more prone if they are being fed an inappropriate diet or interval.

  9. This is so good to know… I was ready to buy worm medicine. We’re pretty new to fish keeping after a friend gave us her’s when she moved away. We had issues with algae bloom and we’re told by someone at the pet store to feed once every two days. Could that be why its poop isn’t always poop?

  10. Does anyone one have help for me please? My betta does have the white long thing hanging for about 7 days and won’t eat and hides at the bottom of the tank. I’ve changed the water and had the water tested and no issues there. I need help please

  11. My tropical fish has pooped four times in less than an hour…white stringy. Looks bloated. I changed Water and he was the only one that survived. Is he sick?

  12. Props to you Dr. Jessie Sanders patience is a vertue, and you my friend have ALOT of it. You don’t seen to loose your patience at all even tho literally every other single comment is another question well hopefully someday people will understand that they need to hit up their local veterinarian if they have questions of any kind regarding their fish. Thank you for taking time out of your day to inform us about the white stringy poop so that we can decipher fact from fiction

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  15. I have a clownfish that hasn’t eaten for a while, is getting skinny and yes (ofcourse) has the white stringy poop.
    I bought a microscope (i can’t take my fish to a vet so i need to d.i.y.) and examined the poop. I was expecting to see parasites (flagellates or worms) but to my surprise the poop looks completely sterile. Nothing moves. (100x/200x/400x magnification).
    Water parameters are perfect. Dr. Jessie, have you any idea what could be going on here?

  16. My Coldwater platy normally loves it’s fish flakes but recently it hasn’t been interested and it’s poop is white. I am concerned as my fish isn’t like this. Maybe her body is slowing down, she is 2 years old? Does she have a disease?

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  19. Hi, I was just linking this article to someone and noticed this “pingback” article linked which I’m not sure you necessarily want as it says exactly the opposite to your article, saying that in guppies it’s very often a parasite, particularly in pregnant female guppies. I’m guessing the information isn’t valid?

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