The Luminous Sea by Melissa Barbeau
A team of researchers from a nearby university have set up a research station in a fictional outport in Newfoundland, studying the strange emergence of phosphorescent tides. And Vivienne, a young assistant, accidentally captures a creature unknown to science: a kind of fish, both sentient and distinctly female. As the project supervisor and lead researcher attempt to exploit the discovery, the creature begins to waste away, and Vivian must endanger herself to save them both.