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.
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.
What does normal fish poop look like?
Normal poop in fish should strongly resemble the color of their normal diet. Since it is not digested by acids in a stomach, the color will not change from the front to the back.
If your fish like to nibble on algae, they may have some vividly green bowel movements. Although many fish like eating algae, they cannot digest much of it, so it exits the same way it looked at the entrance, just wrapped in a mucus coating.
White Stringy Poop in Bettas
Betta fish are one of the most common perpetrators of the “white stringy poop” myth. Since they are tropical fish, their metabolism is always cooking along. However, if they are only fed once or twice a day, there will be lots of empty bowel movements. Given their digestion, bettas should be fed multiple small meals per day in order to ensure they stay fit and healthy. If you are not around to feed your fish multiple small meals per day, because you have a life, as many of us do, try out this excellent automatic feeder that allows you to pre-portion meals down to the pellet!
White Stringy Poop in Goldfish
Goldfish are another common white stringy poop offender. Goldfish are temperate fish, but can tolerate a wide range of temperatures. Most of the time, they are kept at “room temperature,” around 72-76F (22-24C). This temperature means lots of hungry fish and lots of poop. Like our bettas, if you are feeding a few, larger meals, your fish’s GI tract will be empty much of the time and constantly produce empty, white fecal casts.
Goldfish are also not great feed to mass converters, which means that a lot of what they eat goes out the back end and doesn’t stick around. So not only do they love to eat, but they also create a big mess when they do so!
White Stringy Poop in Koi
Since they live outside, it is slightly harder to keep an eye on koi poop. The time most owners note “poop of concern,” it is floating at the surface of their pond. Since most koi are surface eaters, floating poops will happen occasionally, especially if the fish are voracious surface eaters at that time of year. Therefore, it is completely normal to have a few floating poops, either with or without food in them.
Being outside, koi ponds are much more variable in their overall temperature. Shallower and above ground ponds will fluctuate in temperature much faster than deeper, below ground ponds. As the temperature varies, your koi fish’s digestion will also vary. This may lead them to be hungry and produce few poops, or not very hungry and produce lots of poops, or any combination thereof. As their metabolism fluctuates, you may see more or fewer white poops, depending on the time of year, diet and temperature fluctuations in the pond.
White Stringy Poop in Tropical Fish
Usually kept in a group and typically smaller, the bowel movements of small, tropical fish can be hard to observe. There is also usually another fish in the tank who make it a habit of cleaning up the remnants of their tank mates, so observing any poops may be a fruitless task in a mixed community tropical fish tank.
The concludes the lengthy discussion on white stringy poop in fish…
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.