Discussion on question by Ichthys King: How could these aquatic humans survive and reproduce?

The question asks about a life-cycle, but you haven't supplied one. If you wanted an answer that completed the cycle by linking the final human-like forms with the original fish-like ones, then it would be nice if you could state it explicitly.

(a) Version #5 is a high concept question that should remain closed. Describing a cool creature then asking us to invent everything else about it is the essence of an HCQ. Please ask specific questions per the help center. (b) Version #5 is also inconsistent. You can't have an adult fish bear a "tadpole" that then morphs into a human without that human either birthing the fish (that in turn births the tadpole) or later morphing into the fish (that births the tadpole).