Shinkaigyo no Anko-san

Fish people have been welcomed to the town where the human girl Wakasa Otomi lives, and they are integrating well. The fish people can be identified by the physical marks of their fish species, though they take medicine to keep their lower bodies human rather than a fish tail. Otomi loves fish people, and is eager to meet as many as she can! One day, she meets a new transfer student, a lantern fish girl named Tsutsumi Anko. Anko is a bit self-conscious about being a deep sea fish, with a tail that is not cute like some other fish girls. At school, she and Anko deal with various fish problems that intersect with issues an ordinary human high-schooler would face.

(Source: MangaHelpers)

Included one-shot:
Volume 3: Cast Off!