Reincarnated As a Fish is a Manga/Manhwa/Manhua in (English/Raw) language, THRILLER series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

On the verge of death from the betrayal of his trusted colleague, 'Lee Yoo Shin' sees a ray of light moments before dying. "Do you want to start a new life again?" When he came to his senses, there was a vast reservoir in front of him and his body had turned into a fish. Will he be able to overcome all the hardships and return to his family's arms?