You wouldn’t, because goldfish never get pregnant! Their eggs are released to be fertilized on the outside of the body. There are however, some fish that do get pregnant. The most common example, and as their grouping name suggests, are the livebearers such as guppies, mollies and platies. The male of the species delivers their milt into the female by way of a modified anal fin that is curled to form a straw-like inseminator. The female will carry their babies to term and then give birth to live young.
So, although goldfish don’t get pregnant, other types of fish can.
