Be mermaids

Mermaids have scales so they aren't mammals. They lay their eggs on the seabed and a male mermaid comes along and spreads his sperms all over and tiny mermaids or mermans are born.

Well, I, like mant people, feel mermaids would more than likely have dolphin tales sort of. ( but biologically speaking, any hope we have for a mermaid ATM is a manatee ) so they would have periods but I'd assume the same way ocean mammals do

But...if we are talking actual mermaids ...theyr reproductive "parts" appear to be fish ...