As the Economist explains:
Both stories are set in a government-controlled laboratory during the cold war. Both feature a cleaner who develops a relationship with a captive sea creature, dancing in front of its tank with a mop to a love song and devising a plan to smuggle it to safety in a laundry cart after she learns of plans to kill and dissect it.
However, there are many differences in the stories, and ideas are not copyrightable. While a detailed plot and characters can be protected under copyright law, the fact that two works share certain similarities does not mean one infringes the copyright of the other. It's complicated.
As Mark explains, "Unlike patent law, the first person to publish a creative concept does not own it. “If two people come up with the same story independently, without borrowing from the other one, they both get the copyright in their work,”
Read he full article here .