What is this ?

Hello and welcome the to forum Breeshi

It looks like an aquatic worm, like Amphileptus but bigger. Most of them are harmless, eating microscopic bacteria, some parasite snails or shrimps. Once you add fish they will be quickly eaten but if you are bored, take them out with some pincers.

Thank you lol I was like crap I don't even have fish yet and here's this monster ruining it.

I would vote for some type of leech- the use of the mouthparts for locomotion is a bit of an indicator, as is the "slinky" stretch and contraction.

There are apparently herbivorous leeches, but if this is in fact what it is, it might be bad if you plan to have fish and/or invertebrates in your tank.

Bump: I would vote for some type of leech- the use of the mouthparts for locomotion is a bit of an indicator, as is the "slinky" stretch and contraction.

There are apparently herbivorous leeches, but if this is in fact what it is, it might be bad if you plan to have fish and/or invertebrates in your tank.

Bump: Sorry, must've double-clicked by mistake!

Jeff B. said:

There are apparently herbivorous leeches, but if this is in fact what it is, it might be bad if you plan to have fish and/or invertebrates in your tank.

Click to expand...

Wait ? How are herbivorous anything bad for fish and invertebrates ?

Most flat worms move as you describe, but hard to identify without a microscope and most are not leeches. We should consider how common and how plausible it is to have a transparent leech in a newly started, fishless aquarium.

For the worm... the fish is the real monster >

Oh, I agree, it'd be great fish food. But, if it is a leech, then I wouldn't take chances. I've never seen flatworms move in the concentric/accordion style like this video. But I have seen quite a number of leeches do so (even in my freshwater lake in the northern U.S.... swim at your own risk!)

And no, I didn't mean a herbivorous leech would be bad- just that with the difficulty in identification that it might be best not to take a chance.

Nah, good if it is only one easy to take out...but they usually come in pairs. Either way no harm done if you remove it. One thing is sure, do not medicate your tank for them.

I would lean towards a leach as well... although I've never seen a "clear" one before.


Never had any flatworms move like that.