Mosquito Fish

you are welcome; is this is a garden pond it would be stocked with what is sold at the local pet store :)

A tadpole has a fin that is vertically above and below the tail. Here is a great graphic for what a Tadpole fin looks like before you can see the legs of a frog appearing: http://kids.britannica.com/comptons/art-52902/The-eggs-of-a-leopard-frog-develop-into-tadpoles-in :)

Probably a species of Gambusia http://en.m.wikipedia.org/wiki/Gambusia

fish