[AlaninCarlisle]

Almost exactly a year ago I had a 4m x 7m wild-life pond dug and apart from a load of aquatic plants, introduced a dozen gold-fish. The pond has since been colonised by frogs and there are several clumps of spawn there. But curiously last night, I spotted a small black fish, maybe 1 - 2" long. Is it possible that the quite mature goldfish have bred, or is the explanation likely to be that a trespasser has introduced it?

[8doubles]

Yep, the goldfish have bred already !
They eat most of the eggs and fry but one or two always survive even in tiny ponds !
The black/ uncoloured goldfish can take as long as 3-4 years to colour up

[8doubles]

Might pay to move most of the frogspawn to a fish free water butt or even move the fish !
I have seen a  1"  long brown goldfish literally stuffed to the gills with tiny taddies , it could not fit any more in !
 Toad taddies seem to be unpalatable to fish but frog taddies are breakfast , lunch and tea !

[AlaninCarlisle]

We'll just leave it to nature. It IS a wildlife pond and fish are every bit as wild as frogs 

[JayG]

I've had my pond for at least 10 years now, and the original 5 all-gold goldfish are now around 8, having been up to about a dozen. Only one of them is now golden, the others are a mixture of gold and cream, and yes, there is one apparently fully-grown goldfish which is jet black (only noticed it last year as it doesn't exactly stand out amongst the vegetation!

Frogs continue to spawn there, and there continues to be heavy losses of tadpoles thanks to the goldfish. I like to think that some do probably survive by hiding in the tangled mass of roots of the flag irises and other marginal plants, as well as behind the planting containers and in the odd untidy fold of lining PVC.