Hi... Anyone here good at identifying fish?

I have a three tiered pond. The top is the mechanical and bio filter with a water fall into the second which is a vegetation filter, which has a waterfall that returns the clean water to the bottom pond which holds my fish.

My question is:

About two years ago, while we were cleaning the "vegetation only" pond out, we found a small fish (about an inch long) where there should be no fish. It was late fall, and we did not know what kind of fish it was so we brought it inside and after quarantining it, put it in a tank with a few small gold fish and a young koi. I am attaching a picture of it because it is getting a bit too big for the tank, but I am afraid to put it in the pond. Since we don’t know what it is, I don’t know how big it will get, and if it may prey on young fish in my pond. It has done well in the tank, and gets along fine with its tank mates, but is way faster than the other fish. My guess is that it was introduced into the pond as an egg on plants, a bird, or maybe a frog.

I’m hoping someone can help me identify this guy so that I can make a good decision on where it can live.

BTW: As we were scooping some water out of the vegetation pond a few weeks ago, we noticed some fry swimming in the water of the bucket we were using. We are now watching to see what they turn out to be… I see this as a big problem because there are not supposed to be fish in my middle pond for my filtering process to work…just vegetation. Anyone else have this problem?

sandy

Hello that looks like a common carp to me they do tend to grow very large in large ponds lakes & rivers. It will be ok to put into your pond.

Yep. Thats what I was going to say, carp.

its definately a common carp

Well if it's a middle pond then it may have floated in from the uppermost pond.

i have had fry go through my pump and filter in my lower pond and end up in my top pond.....survival.

I used to have to rescue fry from my upper waterfall after they survived the pump blades and 25' trip.