Question
my husband was cleaning filters yesterday found 2 little fish almost look like minnows  how is it possible for them to be in my pond i have a plastic  500gal. pond 4 koi  2 butterfly and goldfish

Answer
They may be baby goldfish which start life as brown/gray/blah fish.  They later change color.  If they're not goldfish or koi (koi aren't as likely to breed, especially in a small pond), then some animal may have brought in the fish or fish eggs.  Fish eggs sometimes come on live plants as well.  Good luck with them!

Robyn
fishpondinfo.com