An Old Tale of Mermaids

In a land long forgotten by time, but most assuredly far away, there lived a little girl.  She was always sent to the river to fetch water by her family, and she always took a very long time to do it. 
Eventually, she was not a little girl anymore, but a young woman, and she had many more chores to do.  It was thought that she should know better than to dawdle when there was so much work to be done.  Her family was finally tired of waiting for her, and one day her brothers were sent to watch and see what she was doing.
They followed her down to the river and watched her sing a song they had never heard before.  While she sang, the river sparkled and swirled and rose up in front of her in the form of a young man and then there was a fish!  A large fish.  She and the fish talked for a long time, while her brothers watched.
When her brothers returned home and told their mother and father it was decided that they would kill the fish as they were a poor family and it would feed them for days, and that it also must have their sister under a spell.
They went to the river the next day and sang the song she had sung.  The sister did not know where they had gone.  When the big fish appeared, they killed it. 
The mother smoked it, and they had some for dinner.  The sister went to take a bite and a voice whispered, "Do you know what you are eating?"  She replied that she did not, and the voice told her that it was the body of the fish, her love, that she was about to eat.  She was horrified, but the voice told her that it would be ok, she just needed to trust him and do as he said.
He told her to eat the fish, as it was only a vessel to communicate with her, and then to head to the barn where the heart of the fish had been thrown to the pigs.  She was to get it, wrap it in a kerchief, and bring it down to the river.
She ran out to the barn taking her kerchief off as she went, wrapped the heart in it, and ran all the way to the river.  Her brothers were stunned, and of course they followed her.  They found her in the river, dipping the heart in the river while singing the song.  As the water rose up into the form of  a man, the heart disappeared and there, standing in the river in front of their sister, was a Mer-folk.  He put his arm gently around their sister, and told her that he was going to take her to the sea to live with him in peace.  He then turned to the brothers and told them that he would turn them into fish because they had not care for their sister's happiness.
This is the story of how Mer-folk came to be.