Stringy White Fish Poop: Normal or Sick Fish?

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.

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.

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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