Studies involving how fish respond given different flow field conditions are important in understanding phenomena such as fish schooling as well as larger‐scale migrations. Simulating a fish moving under various flow field conditions is a difficult task, however, due to the fact that fish responses are dependent upon the environment. This makes the traditional use of analytical expressions to model the movement of fish bodies intractable. Thus, the main focus of the present study was to establish a method for coupling the use of image‐analysis‐based techniques for determining fish body motion with the use of a computational fluid dynamics (CFD) simulation. In particular, we focused on the simulation of a fish (rainbow trout Oncorhynchus mykiss) swimming behind a D‐section cylinder. This simulation was based on previous experiments that studied how vortices being shed from a blunt body affected fish movement. The individual frames of a video depicting a fish swimming behind a D‐section cylinder were segmented, and the resulting x, y coordinates of the fish's body were supplied to a CFD simulation to capture the fish motion. The CFD simulations were performed by using a k– turbulence model to calculate the flow field. Previous experimental results showed that the fish traversed between the shedding vortices. Our computational results show that the propulsive force is greatest when the shedding vortices pass along the sides of the fish body in order to aid in its movement. Future work entails extending the analysis to three dimensions and including more details in the fish geometry.