Research in robotic grasping and soft machines has demonstrated that the use of “smart” mechanical structures in robotic systems can enable complex behaviors in dynamically changing, uncertain environments without the need for complicated, low-level control strategies. Upon that premise, we designed an 1DOF simply controlled robotic fish to explore the ability to achieve different locomotion patterns and passively generate adaptive swimming behaviors, simply by changing the servo’s output parameters. This 1-DOF, cable-driven robotic fish mimics the cascaded skeletal structure of soft spine tissue and hard spine bone seen in many fish species using a series of rigid segments and elastic joints. By changing the frequency of actuator motion, the robotic fish can not only change its lateral swimming pattern from oscillatory (2.3cm/s) to undulatory (11.0cm/s), but also change swimming direction from forward to backward and steering by biasing servo sweeping offset. Preliminary tests also show that the robot can swim downward to 7m successfully. In addition, the soft body helps the fish passively navigate through gaps and around obstacles without any feedback control, greatly enhancing the locomotion robustness in complex, cluttered environments.