I've mixed fish from different sources and had no trouble.

I suspect fish are already pretty inbred, probably doesn't make much difference.

And gotta ask, it took TEN YEARS for them to breed? Mine got started at about age 4. Maybe it's the climate, or pond size, or plants, or...

Hi
Don't have much experience with GF but kept tropical fish.(Red wag swordtails for over 20 years . beginning with
4, two males two females depending on temp they can mature in under two months but even if you figure 3 that's still 60 generations ?? lol I'd say that was inbred??lol
They were still having viable offspring when wiped out by the deep freeze of 09. Evolved into over 25 color/fin types over the years BUT red body,black fins still dominated !!! gary

The reason they did not breed for many years cos they were in pairs in large utility tubs outside in summer in in winter they only got their pond two years ago. They may not even have been male female pairs of maybe the cramped space made them too depressed to breed. Luckily they have not passed menopause or whatever the fish equivalent is now!

You don't need to add new fish but if you see one that you like the looks of... sure! Don't add ugly fish - they will reproduce more than ALL the others. LOL
Big fish eat eggs and little fish. Little fish learn to hide until they are big enough, then they join the rest of the school. Usually within a couple months of hatching they are hanging out on the fringes of the group. Sherry