In this paper, two case studies in which biomimetic robotic fish have been used, are described. Biomimetics is an analytical and synthetic process by which biologist and engineers duplicate biological structures, function, or both, and apply them in mechanical machines, robots etc. Biomimetic robotic fish are built for three reasons: to test biological hypotheses, to engineer novel designs for underwater vehicles, and for entertainment or education. First, biologists and engineers formulate the intended function or behavior of the robot, the processes that will create the function or behavior, and at the end they make design plans. Robotic fish are built to model individual structures, particular species, or whole populations of fish. Robotic fish may or may not be self-propelled, behave autonomously, be powered by on-board batteries, or be controlled by computers. Many robotic fish projects study propulsion, with body and fins built to produce biorealistic locomotion.