This work documents the creation of a fish-inspired robot actuator - from the conceptual design to a functional silicone model. The effect between the variable stiffness of a fish body and swimming efficiency has been a research subject in recent years. Often anatomy or function of an organism will inspire technological designs, particularly within the study of robotics. Animals have flexible anatomy for a range of possible maneuvers, and why fish-inspired robots are a popular choice in research. Studies have suggested a key to swim speed and efficiency in fish has been through tunable musculature. While muscle stiffness is difficult to measure in live fish, there is strong, natural evidence from several species, such as sunfish and tuna fish, showcasing this idea. Promoting inspired designs is the next step in improving robot performance. The deceptively simple appearance of typical fish combined with the numerous species' traits provides several possible robot designs. The robots can be objectively simple, with a trivial body and motor design to observe simple caudal fin motion. Or they can be exceptionally complicated if the research chooses to explore the nuances of fish anatomy and physiology, and how the impact on fish swimming in nature translates into an engineered construct. This would be beneficial due to the close relationship between bio-inspired design and soft robotics, fish bodies make a prime testing ground for soft robotics. No matter the simplicity, these robot designs can then be tested to gather valuable experimental data. This collaboration of technology and analysis then results in robots with advanced designs and special maneuvering capabilities. This research project aims to develop a tuna-inspired tail actuator capable of variable stiffness via a pneumatic system. Once attached to a 3D-printed fish body, it will be used to observe vorticity changes in fluid.