Lifecycle of a Mermaid
Merfolk can be born one of two ways. Some are hatched from eggs like most fish and others are born live like human children. This doesn’t affect their growth or maturity in any fashion except their size at birth. Hatched merbabies are about the size of a small trout where those that are born are about the size of an average human newborn. Both have very basic, relatively shapeless tails, the scales closely resembling those of a brown trout. The fins come in three shapes; crescent, whale, or spade. A baby’s tail has little impact on their mature tail. At this point the child will look like someone cut the head off a trout and stuck it on a baby’s body. They also have pronounced gills on their necks and ribs, entirely unable to breathe air. From here they will develop and age like a normal human.
As the child gets older their tail begins to gain shape and the old scales flake off. By age five the scales more closely resemble a rainbow trout. The tail has now shaped to the hips, and will continue to grow with them. The end of the tail will change with the scales but the shape will remain the same. They still have their gills though they are less pronounced. Small fins may develop on the sides of their head near the ears.
Between nine and twelve comes the first major change. They will shed their rainbow trout scales and develop brightly colored scales. This color does give an indication of their mature tails color, though the exact look of it is still a mystery. It is also at this point that they begin to lay eggs and produce sperm. After the tail has changed they will go to the nesting area. Females will lay their eggs and leave them to be fertilized by the males. Those who have found someone they wish to reproduce with may do so in a solitary nest if they wish. These eggs will be cared for by Nestmaids, mermaids and mermen who are unable to produce their own children. They will also begin to lose the gills along their ribs. Fins on both the tail and head will begin to change size and shape.
Just before sunset on their sixteenth birthday they will swim to the surface with their family and friends. They will remain below the water while their mature guests take places on the rocks as well as in the water. One by one those turning sixteen will leap out of the water and over a staff being held above the waves by a priestess. As they breach the surface they will briefly lose their gills and fill their lungs for the first time. Upon diving back into the water they will regain the gills on their neck but the gills on the ribs will be lost. Their tails will change into their final shape and color, with little to no predictability. From this point they are considered adults. They are now allowed to spend time above water, singing on the rocks or exploring The World Above. They can also reproduce with or without eggs. Once a year females will deposit eggs unless they have become pregnant. Males may now produce sperm at will.
The majority of merpeople are born from eggs, just for the sheer number. While not all fertilized eggs will make it to hatching, those that do hatch add to the vastly diverse mer-species. When mermaids reach puberty they will deposit a clutch of eggs once every three to four weeks. Pubescent mermen will deposit sperm to fertilize these eggs. Any children that come from pubescent clutches will be raised by Nestmaids rather than thier actual parents.
After merfolk reach adulthood, they may choose to lay and fertilize eggs outside of the nesting area. There are many reasons they may choose this, including having bonded with a sea creature or wanting to avoid any potential commitment to the other parent. Wild hybrids, often considered to be Feral, are more likely to show traits from their wild parents. This may include tentacles and eel tails, bio-luminescent antennae, rows of sharpened teeth, and rounded fish eyes. While these traits may appear in domestic clans, they usually indicate a Feral ancestor and are thought to be more common in the Deep.
As adults, merfolk are also able to breathe oxygen and walk on land in The World Above. Young adults are encouraged to make short outings and learn the ways of the humans before attempting any long excursions or sexual relationships. Romance is highly discouraged, but mating with human men and woman has been a tradition for centuries that no one argues with.
When a mer goes Above, they will often find themselves in a coastal town or village and choose someone here to mate with. This has led to local legends in many countries about mysterious and beautiful men and women who sleep with an unsuspecting villager. When they are Above, mer-persons will appear entirely human, though many reports describe them as having an 'otherworldly' beauty. Their voices can entrance humans, making it easier to convince their target to take them to bed. Once there, the sexual act can take place as it does for all humans.
Mer-women who have conceived with a human male must return to the water they came from to give birth. They will be unable to resist shifting during the birthing process and the child will not have lungs to breathe the air of their father. The mother will then return to her clan with the newborn to raise them until they come of age.
Human women often find the process more difficult. In the best case, the man they have come to care for will take them to the beach instead of the hospital. For some, they have conceived unexpectedly with a man that may have vanished before morning and will return within six months to claim his child. Anything to ensure the baby is born in the water, to keep them alive. In the worst, they are left alone, unaware of what they are giving birth to. The ultrasounds will show a healthy, normal baby that takes after it's human parent in it's human womb. But within moments of emergence, the child will change and begin to gasp as it's gills flutter open.
The majority of merfolk have mammalian genitalia in addition to their egg sack, due to their human ancestry. Those with three or more mammalian ancestors, including dolphins, humans, or seals, may only develop mammalian genitalia and only be capable of live birth. These mers will be limited to reproduction with humans or other mammal species.
In rare cases, the child may be born with a unique mutation of their design. Children may develop their fish halves on top and their human below, impairing their ability to swim and defend themselves. Children conceived with humans have been born entirely human but with a connection to fish or the ocean, should they live. They have also been born Feral to both mer and human mothers, babies with shark teeth attempting to get their first taste of flesh.