Given the huge amount of evolution that mermaids must have clearly undergone, it seems likely that even if mermaids are primates they may well have evolved away from a menstrual cycle given its likely disadvantages underwater. read more
No, because sharks would smell the blood and eat them. It's more likely that they reproduce by laying eggs, like other fish. read more
or, Explaining The Menstrual Cycles of Various Mythological Creatures That is menarche! Er, sorry, malarky. Either or. read more
To answer this question really depends on how you define a mermaid. However , if you include an animal that has human traits that have evolved over time which enable it to live for most of it's life in a marine environment, then I think that this is definitely possible. read more