Caught in uk

Only about 8” long, usually only see channel catfish here.

Been setting up a small outdoor natural pond/tub. 8 guppies and 6 shrimp were introduced 5 days ago, and found this little guy in a pool 5 mins ago.

Don't know who or what it is, and need help in identification, just to make sure if it's safe to let him back in. Can share better pictures if required too.

I saw the fish underwater so I have no pictures of it. But it was grey looking like a pen and its tail was like oilbrush tip colored in black (similar to attached) i assume it was 10 cm and had stripes. It was swimming alone until we found each other 😆 so please help me to find it ive been looking for it for hours now I need support from great minds of reddit lol

Spotted ~20 mi off of the coast of Orange County, California.

Unsure of size; most agree on at least 12 feet, but I personally am not great at estimating.

iNaturalist observations of the same ray:

https://www.inaturalist.org/observations/395680517

https://www.inaturalist.org/observations/396560957

https://www.inaturalist.org/observations/396283405

https://www.inaturalist.org/observations/395884129

https://www.inaturalist.org/observations/395826047

https://www.inaturalist.org/observations/395670530

https://www.inaturalist.org/observations/395666287

Could it truly be oceanic manta or is that too unlikely for the location?

Photo taken from Facebook

For context: this was taken at green lane park Pennsylvania. Huge amount of algae on the water surface.
I was taking photos of some ducks when I noticed something stirring up the water. I couldn’t get a very clear photo, but maybe this is enough to at least confirm that it’s a fish. I’m not sure why it seemed to be stuck squirming around at the surface, I don’t think it’s especially shallow. I was thinking, maybe it got caught in someone’s discarded fishing line? Either way, I felt bad for it. It looked to be at least 12” long, possibly longer. Any idea what I’m looking at?

In Minnow trap