Fish babes are pretty weird lookin. Whale and dolphin mers are pretty cute tho.
In this world, there are two different kinds of merfolk, warmblooded and coldblooded. Warmblooded children are live born; beautiful, cute children that learn to swim quickly on their own, and grow even more quickly when nursed, and… over time they mature into equally cute adults.
Cold blooded merfolk, however, have the lucky trait of born looking like complete aliens, and also at an extreme small size (hence why children are called “fingerlings” as many are the size of a single finger). Some are born in great egg broods, others are live birthed, some with yolks still attatched. Cold bloods have been known to reproduce in great numbers in the past, although often not as much in recent centuries, nor at the same rate as their familiar fish cousins. They forego the pitfalls of being overpopulated by having significantly shorter life spans than warmbloods.
Depending on how they are raised, these fish mers will EITHER grow into looking more fishlike, or human. This depends on where the mer lives, their relationships to their self, to others, and religion.
Children living in Pilgi, are usually followers of Coral Gods, trading the gift of fertility to that of a prolonged life span and Dream telepathy. These mers are highly social, will integrate coral organisms into their own biological system through Seeding, in order to create highly intricate social structures and shared thought processes, called the Dream. Many merfolk following this religeon, and following the Seeding, will find their bodies undergoing a shift from their big eyed facade to sea anime, to human-like features.
In contrast, those fish born in Banthi, the deep sea, are often highly independent, and will sometimes be born without every seeing their kin. These mers have to learn to rely on themselves, often from birth (many will be able to feed themselves and be fully capable of basic survival as soon as they are hatched). Many follow the god Wyrm, a religeon of self reliance, of inner strength, fertility, and passion. These merfolk take comfort in their familiars, and they will tend to change over time to look more like them. Some rare few will even shift so far as to become nearly indisginguishable from the fish itself, others might become draconic in nature- and become feral. These kinds of mers are called Naguals, and it is looked down upon, even illegal to make a full shift due to the danger a feral mer-creature presents, they are very uncommon.
Change to either side of a spectrum can happen at any time in a mers life, with some difficulties. Interestingly enough, there is no aesthetic preference among coldbloods, they find both fish-like and human-like features equally attractive, but religious reasons may decide how they pick their mates on appearances.