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I have recently noticed these tiny creatures on the glass and other surfaces in my aquarium. What are they, and where could they have come from? They are about the size of a sesame seed and growing.

They don’t seem to be harming the fish, and they seem to be eating algae off the glass, and lots of it.

About the aquarium - 55 gallon unheated tank with a single bluegill sunfish in it. The tank has been setup with this lone fish in it for three years and has been very stable. I feed the bluegill a live “nightcrawler” earthworm every few days. They are the only things entering the tank.

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paul
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  • to identify them i need a better picture,one way to take a better picture is to turn off the light in the room so the only light is the one in your tank and be sure you get them in focus.a scale is helpful too it is hard to see the size of them. – trond hansen Jan 06 '20 at 16:02
  • from the information you provide i think i know what it is but a better picture will confirm it. – trond hansen Jan 06 '20 at 16:12
  • What do you think they are? I will try for a better photo when I get home later but this might be as close as I can get while keeping them in focus. – paul Jan 06 '20 at 17:39
  • i think they might be eartworm cocoons in essence egg capsules from eartworms.but there is several other things it can be. – trond hansen Jan 06 '20 at 19:48
  • They were not present on the glass when I got home. I think they might hide during the day and I find them in the morning on the glass when I first turn the light on. – paul Jan 07 '20 at 04:14
  • Like I thought - they are there this morning, all over the glass. The picture I posted is as good as I can get with the camera I have, and was taken with just the aquarium light on. What else do you think they could be? They don’t seem like eggs since they can move. Like I said, they are the size of a sesame seed. – paul Jan 07 '20 at 12:35
  • i do not dare to give you a definite answer on this one but it might be some sort of ostracod https://en.wikipedia.org/wiki/Ostracod but i am not sure they hide from light. – trond hansen Jan 07 '20 at 14:01

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