A remote-controlled underwater robot fish is described. For motion control three actuator drives are used: one actuator is for tail frequency exchange, the second actuator is for the left or right turnings and the third actuator provides neutral swimming or up and down diving. From the robot's center of mass motion theorem (according to the given total mass of robot) the proportional distribution of massesof structural elements is found. Experimental indoor and outdoor investigation of robot fish is given.