I recently found a baby frog when i was buying feeder fish for my oscar?

2 days ago a lady was scooping feeder guppies out and she scooped a BABY frog out accidentally, she said i could keep it and put it in another bag without water and kept the top open. whan i got to the front checkout the man said i needed water in with him to he got him some water. (long story short) i got home and put my feeder fish in a separate tank and i put him in there but he was having trouble swimming so i put him in with my baby guppys in a breeder net with anacharis and he was doing fine (he is less than a centimeter long) i want to identify what he is he is brownish black like a baby toad but much smaller and smoother he has little black spots/streaks on his back darker than his other colors. please help. one more detail: he gets on the side of the net out of the water to breathe them gets back in the water. he has lost part of his tail (tadpole tail) over the last 2 days