I don't know. Does anyone? You won't really know unless you get babies - or not....
My grand-daughter Lucy (age 5) had 3 Goldfish, which she called Daisy, Ruth and Bubbles. Unfortunately, Daisy died last weekend and Lucy was inconsolable.
A garden burial was rejected, as was flushing Daisy down the loo. Daisy had to be kept for 24 hours (in case she miraculously revived) and had to be quietly disposed of the next day, during school hours.
Daisy has now been replaced by Sunny (a bright yellow goldfish) and all is now well - but we don't know whether it's male or female - and we don't care, either.