[Diana]

"...2 small spokes out of the back..."

Aphids have this structure. Don't remember what it is called.
Aphids do not go under water (except by accident).
Fish will gobble aphids like candy.

There are certainly other bugs it could be, too.
Google some images of Springtails. These are a lot more aquatic than aphids!

 

[Diana]

Slosh the plants around under the water as often as you can.
This will wash off the aphids and the fish will eat them.