I've been noticing these really small creatures (or plants, I'm unsure) in my tank recently. They measure less than 1cm in length and I've only seen them at the bottom of my tank; some attached to the gravel and some to the glass. They have tentacle-like appendages on the end of their stem(?) and seem to drift with the with the water movement rather than on their own accord.

My tank is a planted tropical freshwater.

What is this plant/creature in my tank?

Any additional information on whether or not these are harmful to my fish would be appreciated.

  • 1
    $\begingroup$ coooool! You are so lucky to have such cool creatures. Feed them! $\endgroup$
    – Willk
    Commented Sep 19, 2017 at 17:28

1 Answer 1


That is a hydra.

They are a kind of jellyfish, and as such they do technically have stinging tentacles. However, they're also very small, so they're not a danger to most fish or shrimp. If you're planning on breeding your fish they will eat fish fry if they get a chance. On the other hand some fish species will eat them, so it's a bit of a wash.

Generally they only thrive in tanks with extra food hanging around, so you may consider feeding a little less than you have been.


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