What is This?

[JemZ]

Cleaned my tank today, found this guy right at the top. I assume it got out from under the gravel when I was vacuuming.

 

[Sgooosh]

Cleaned my tank today, found this guy right at the top. I assume it got out from under the gravel when I was vacuuming.

think i need a better photo. it maybe is a mosquito larva, what fish do you have?

 

[JemZ]

I won't be able to get another photo since I don't know where he is now. It was small, grey/silver, and when I found it, it was being pushed by the current to the front and was constantly spasming. The other fish in the tank are a Chinese Algae Eater and a swordtail.

 

[Essjay]

It looks most like a piece of fish poop twisting in the flow from the filter. If you cleaned the gravel it may have been in there and partially decomposed so with gases inside which made it float.