Can anyone identify this fish species? They have shown up in my pond this season. I haven't seen any mature fish yet. Common schooling habit, largest fry in front followed by a general same size class of 100 or so. They will breach the surface when threatened. Any info would be appreciated. 5 acre Pond in Northern Illinois. Known fish species: Grass Carp, Channel Catfish, Northern Bluegill, Hybrid Bluegill, Green Sunfish, Largemouth Bass, Black Crappie.

Looks like a Silverside minnow to me.

Excellent, thanks!

See if this helps.

https://www.efish.fishwild.vt.edu/families/atherinidae.html

https://www.efish.fishwild.vt.edu/families/slenderchub.html

https://www.efish.fishwild.vt.edu/families/streamline.html

https://www.efish.fishwild.vt.edu/families/cyprinidae.html

99% sure it's the Brook Silverside. Thanks for everyone's help.