I'm on another forum and a couple members have plecos which seem to poop a white stringy substance occasionally. The fish didn't seem sick in either case. Is this sperm? Is is something they are eating? Is this parasites or a reaction to their environment, toxins, etc? We are clueless as to what this could be. I have a pleco among many other fish in a very healthy 100 gallon planted tank, and I've found something that looks like a regurgitated stomach lining twice. I wasn't losing fish, so it must have come from one of mine. I don't know if it's the same thing my friends are talking about. Any answers? Thank you in advance. garman

Where the strings hollow? I've had my plecos in the past poo out empty fecal casings, basically there's nothing inside them. In those cases, the fish was feeling ill (intestinally). It definitely is not sperm which comes out in a very tiny cloud during spawning. If plecos eat whitish algae or other white food, that could give them white feces. General ill health from a bacterial infection, starvation, parasites, etc. certainly can result in hollow or abnormal feces. All sorts of strange things can come out from the vents of fish. It's not likely to be actual sloughed intestines but sometimes, if the fish has an irritated intestinal lining, some of those cells might come out. I've found white floating skin-like things in my tanks sometimes. They are usually shed skin from my African dwarf frogs in that tank but sometimes fish may slough off some skin. That's usually not a good sign.

If your fish otherwise seem fine (eating, behaving normal, water quality looks and tests fine), I wouldn't fixate too much on their waste.

Thank you for your advice.