Assessment of the Critical Thermal Maximum (CTmax) of Iberian chubs v1

The upper thermal tolerance of organisms is usually reported as the Critical Thermal Maximum, or CTmax. Here, we describe an adapted protocol to assess the CTmax in the Iberian freshwater fish of the genus Squalius, commonly known as Iberian chubs. The protocol involves exposing individuals to a controlled and progressive increase in water temperature until the point of loss of equilibrium, i.e., uncontrolled and disorganized swimming followed by loss of dorsoventral equilibrium. This point is recognized as the upper thermal physiological tolerance of individuals (i.e., CTmax). Although we applied this protocol exclusively to the Iberian chubs, it can potentially be adapted to other freshwater fish.