Efficient inhibitory control has often been considered as a distinctive feature of humans and vertebrates with large, complex nervous systems. However, recent work suggests that fish, despite a relatively small brain size, are capable of solving inhibition tasks and that their performance is comparable to that observed in vertebrates. In ManyFishes 1 (MFish1), we use a version of the detour paradigm—the cylinder task—to test inhibitory control in several fish species. In the task, subjects must swim around a clear obstacle (cylinder) to obtain a food reward. Importantly, they must inhibit their motor impulses to reach for the food directly by moving away from the goal, thus avoiding to bump or touch the obstacle along the way. Advantages of such task is that it is simple to implement, is flexible and inexpensive, requires minimal exposure and training, and is applicable to a wide range of species and settings.