The most likely explanation for the variation is the offspring were produced from different combination of genes. A single pair of gold fish mentioned in the question means a male and a female gold fish. The two of them mated and contributed different genes to the fertilized fish eggs, this results in production of various body shape and colouration which is known as variation.
Explanation:
Pride is the social community of lions where they grow, mate, reproduce, communicate, hunt etc. When male lions gets control of a new territory or a pride, they most of the times kill the cubs of the pride because they are not biologically related and do not want to waste their energy by ensuring that the cubs genes are passed on.
They don't want to be stepfathers. Female lions also will not be responsive to mating during the time they are feeding, so killing the cubs allows the male lions to reproduce.
A hairstreak butterfly my dear.
