Canonicity: To Be Decided.

In short, mermaids are fish people with a very unique biology who just want to hear a good story. 

Biology:
Mermaids are a mixture of both fish and human. Their lower half is that of a fish, usually one that is predominant to the area. The lower fish tail is used to easily swim through the ocean, propelling them to speeds of up to twenty miles an hour. This tail is covered in scales of the fishes type, and is perfect for them to slip through the water. The top half of a mermaid is that of a regular human, typically a female. Most mermaids are roughly between 5”6 - 6” ½ feet long/tall, and can weigh up to 400lbs (albeitalbiet very proportionally) (Archivist's note: imagine being that fucking fat. That's a lot of blubber, they should be bullied more.)

Instead of lungs, mermaids have Mermaids can breathe both water and air, albeit with restrictions. Mermaids breath similarly to humans, sucking in water instead of air. There is a specialized organ in their body that works similar to a pump where the diaphragm, sucking in water through their neck gills and jetting it out. This water has its oxygen scrubbed out of it by their gills,  and is replaced with fresh water. When breathing air, mermaids gills function like crabs gills/lungs. As long as their gills are wet, they are able to breath air. This allows mermaids to hang out on rocks, talk with people above water, and function as a human would normally. There are even stories where mermaids have been carted around on wheelchairs on land, with them being able to live in very humid areas without any worry of drying out. 

One thing that allows for mermaids to traverse the ocean and land is their hollow chest cavities. In the area where a normal human lungs would be, there are hollow cavities.  These cavities have a dual purpose to them, for both in water and out of water. A mermaid's breasts function as a form of swim bladder, being able to be used to allow the mermaid enhanced travel in the water when diving or submerging. When a mermaid dives deep, the swim bladders (breasts) get pushed into the chest cavity, protecting them from the dangers of the deep. In normal pressures, or at the surface, the swim bladders allow for them to float normally. In normal pressures, the hollow cavities in the chest allow for the mermaid to store extra water for when they surface. This allows for the mermaid to do one of their favorite activities, hanging out on rocks, talking to sailors, and other above water activities. 

Mermaid reproduction is an interesting phenomena, being that they can reproduce both sexually and asexually. Mermaids reproduce via egg, and they may lay between 30-60 eggs at a time, with a median range of 50. Whether these eggs are fertilized or not does not matter, but there will be differences between fertilized and non fertilized mermaid eggs. With such a large number of eggs, one would assume that mermaids would be plentiful. However, much like the regular fish of the oceans, most mermaid eggs will not survive to hatch. Out of the clutch of eggs, only between 3-5 will mature to hatch. Others will die, being carried of by the currents, eaten by predators, or just not grow strong enough. Mermaid eggs that have been fertilized via sexual intercourse with a male will produce mermaids with different RNA, DNA, genes, and genetics. This will allow for the mermaids to be able to adapt with different traits and have positive genetics. Also, fertilized mermaid eggs have been shown to have a higher survivability and hatching rate than the unfertilized ones. As stated before, unfertilized mermaid eggs will still hatch, bearing offspring to continue the mermaids lineage. The key difference between fertilized and unfertilized mermaid eggs is the fact that unfertilized eggs will bear only female mermaids, with these females being an exact genetic replica of their mother. While this might seem to remove the need for sexual reproduction or mates in general, there are downsides to this method of reproduction. Mermaids that only reproduce asexually eventually fall into stagnation. After several generations of just reproducing asexually, mermaids begin to become infertile. Less and less eggs begin to hatch. Pretty soon, the last generation will be born, and no more of the mermaids eggs will hatch. However, even on this last generation, if the mermaid manages to reproduce with fertilized eggs, the entire process will be jump started. The next generation of mermaids will be able to reproduce asexually without worries, and their new genetic data will allow for them to survive. 

Habitat:
Mermaids have a wide range of habitats, but they are (almost) always in the ocean. Typically mermaids live in the sunlight zone in intertidal areas, usually within the first 100-200 feet being the deepest they are comfortable with traveling (although they can swim up to 800 feet deep at maximum). Mermaids typically make villages in the 20-60 ft area, with the most mermaid villages being found in the areas of 30-50ft. Mermaid villages are like communes, with each mermaid living in the village living solitarily their own “home” (typically a cave, reef, or wreck that has been converted into a living space.). When not living under water, mermaids enjoy lounging on rocky outcrops or sandbars, soaking in the suns rays and greeting sailors as they pass by. 


Behavior:
Despite being solitary creatures, mermaids are surprisingly friendly and sociable. While they do live in their own homes, mermaids often socialize with each other, and are very happy to hear gossip and what is happening. Oral tradition is a beloved thing, and stories are passed down generation to generation. A favorite activity among mermaids is lounging on rocky   outcrops with their friends, waiting for sailors, divers, or any land creature to come by. Mermaids love talking to “land folk” as they call them, finding out what is going on inland and how life is. It is not uncommon for an entire village of mermaids to come around when a traveler is near, listening to the stories that they say. 

Due to living underwater, and a limited access to (or need of) fire, mermaids have not advanced very far with any form of technology. They create very little, having more or less a stone level of technology with primitive tools. What they don't create is typically scavenged from wrecks, or traded from land folk. However, limited tools and technology is not much of a bother to them. Mermaids are very simple creatures, and this is represented by their behavior. Mermaids are not very smart intelligent wise, but they do have great amounts of compassion and wisdom (sometimes). 

Due to their love of stories, books are a prized item in mermaid society. However, this is a very paradoxical thing, as paper breaks down in water. A mermaids favor can easily be won permanently by presenting her a water-proof version of the book that she was unable to finish reading before it dissolved.

Due to the limited (and often unnecessary) need for sexual reproduction, the idea of taking a permanent romantic partner is something that is rarely done. With that being said, mermaids still adore the idea of a spouse and family. The legend of sirens and mermaids grabbing sailors and drowning them to death is real, but only partially. There is no maliciousness to this action, only naivety and unknowing. In their excitement of finding a “Land Folk”, they often unintentionally drown them. Of course, the mermaid does not realize this, and is unaware of the fact that the person has died. They will take the dead body, and play a version of “house” with it; dressing it up in whatever outfits that they have scavenged. 

Going along with their romantic preferences, and simple nature, mermaids are very straightforward, open, and a bit naive, to the point where it might be considered overbearing. Calling a mermaid a friend is the equivalent of pledging your life to them, and telling one that you like (or even love) them is practically marriage, and they might immediately rattle of questions along the lines of “where should we build our house to live together?” or “What are we going to name our kids?”. This leads to some confusion among Land Folk when talking to mermaids, but the real meaning can be explained, often with more than a bit of talking.