All right, something doesn't add up here.
Given that mermaids have a fish tail, I would assume that they have fish-like reproductive organs. But if so, why the mammary glands? Are they merely decorative, or do they serve some functional purpose? (And if so, what?)
Why does one never hear of swarms of tens of thousands of tiny mer-people in the earliest stages of development? I suppose that given that they lack souls, and turn into sea-foam on death, we don't have to deal with questions of at what stage of development they are ensouled. Do mer-people themselves have any rules as to at what stage of development killing or eating mer-children becomes a serious crime?