Yeah, these are bull frog tads...they eat EVERYTHING including algae, koi fry 9any small fish), small aquatic insects and koi food.
I have seen not one fry from this years spawn, probably because the entire bottom of the pond is covered with these tadpoles.
The mature bull frogs are cannibals, they eat their own tadpoles, not to mention each other and all other frog species. All we have now is bull frogs in this pond, because all other frog species were eaten by the bull frogs.
Many of the tadpoles are missing tails, just bloody stumps with cartilage and bones sticking out, because the big bullies snap at them. I find plenty that have died from their wounds too.
Also, crows like to sit at the edge of the pond and pick at any tadpoles that get too close.
Oddly enough, the koi leave the tadpoles alone.