The question of mermaid reproduction has been one of the great enduring mysteries about these beautiful but arguably mythical beings. The answer really has a lot to do with the exact nature of mermaids. The answer to this requires knowing one other questions:
Are mermaids really half fish?
When asked to depict mermaids, most people will draw a woman (either topless or wearing seashells or similar types of bras) down to the waist, and then start green fish scales from there down. These scales go all the way to the base of the tail, at which point there’s usually a “caudal” or tail fin that’s about a meter wide and between a half and full meter in length. When the mermaid sits down, the caudal fin typically runs along the frontal, or coronal, plane; it is flat, along the same plane as the back.
This is not typical of any fish on the planet. On all fish, from sharks to rays to bony fish, the caudal fin is always vertical (sagittal).
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