How many fish in one pond?

Hi guys,

I put 7 fish (mixture of Goldfish and Shubunkins) in my 1000lt pond when I
first stocked it. One died pretty much straight away and 3 vanished into
thin air -I think a Heron or something took them.

Iv'e had Three fish in there now for about 3 years but last week I noticed a
new completely Jet Black fish has appeared. It is clearly a baby but it
dosn't look like it belongs to any of the fish I have already as they are
all multicoloured -do baby fish not look like their parents then?

Anyhow this has got me thinking, what if they keep breeding? How many fish
can I comfortably fit in a 1000 ltr pond and will the fish stop breeding
automatically once they reach this limit?

Any answers would be most appreciated thanks,
Jay :-)