Well, when a mommy fish, and a daddy fish love each other very much, they.... JUST KIDDINGFish actually lay eggs (Only female). When she does, the eggs are most likely in one of those "caves" or on a...
There is no specific difference between a goldfish in a pond or a goldfish in a tank. Under normal conditions pond fish breed once in spring/summer but they can both be encouraged to beed several...
The goldfish and spawn need to be separated immediately spawning has finished otherwise the spawn will be eaten. I used to remove most of the spawn rather than moving the fish.