Is this a Parasite or Pond Worm Leech?

[Goldfishpond]

Does anyone know what this is? I found inside my Pond Thermometer next to my Potted Plant. Looks like a leach but stretches to a flat worm once removed thermometer out of water.
Is it a tiny flatworm or leech, what is it?
Is this a parasite dangerous to my fish?
It’s teeny tiny but 2nd picture is closeup before It started moving & stretching. Once it started drying it moves it looks more like a worm or leech.

 

[Michael from Daytona]

Not a leech. Looks very much like planaria, a common flatworm. Are they parasitic? Probably not this particular species, although tapeworms and flukes are in the same phylum, platyhelminthes. They are ubiquitous, found in nearly all moist environments. I studied planarians in high school biology. Having no digestive system, they absorb “predigested” nutrients from decaying organic matter, just one cog in the wheel of any pond’s life cycle. I don’t think planarians are a direct threat to pond fish but their presence in abundance may be an indicator of low oxygen saturation and/or high nitrate levels due to bacterial breakdown of dead plant matter. They also thrive in stagnant water, so you might take a gander at your overall pond circulation and aeration.

It can be of some benefit to take a closer look at your next test tube pond samples for little critters that might not be noticeable otherwise, such as mosquito larvae, which can reveal information about the condition of your pond that chemical testing might not. I recently found thousands of tree frog tadpoles in my pond that were tinier than the holes in my skimmer net (<1mm). Probably going to be a snack for my comets when they get bigger.

Interesting. I think I’m going to go examine my pond water right now.

 

[Goldfishpond]

Awesome thank you so much!