Discovered two black fish in pond

Hi

We moved into a house over 8 months ago and we knew there was a pond in the garden. They said there was nothing in there but the odd frog which visited.

However, much to my surprise I glimpsed two very quick and very timid black fish in there.

Heaven knows how long they have been in there. The pond is only about a foot deep and a metre wide each way. They seem quite happy indeed - very fast and they dart around like mad.

However, three things have been intriguing me:

1. How come they have managed to live this long with no supplementary food? The pond has lots of plantlife in and around the pond and insect life around it - have they been eating insects falling in?

2. Why are they black? I've tried to look at species and they look like goldfish but are almost 100% black (which doesn't exist in goldfish species.) They are not Black Moors. They are more slender than those.

3. There is no filtation or air machine in the pond.I have no way of doing this easily (no electricity) but they seem ok like this. Someone in the aquarium shop said as there are only two fish, there's no need.

To be honest the pond isnt that great and I never expected to be looking after two fish - but I will if I can get the proper advice.

I bought some fish flakes so am giving them a few. They didn't come over straight away. Not surprised! Imagine having had no food for years then being offered food! They are eating a bit now.

Any advice greatly appreciated

Debs