Behavioural thermoregulation in cold‐water freshwater fish: Innate resilience to climate warming?

Behavioural thermoregulation enables ectotherms to access habitats providing conditions within their temperature optima, especially in periods of extreme thermal conditions, through adjustments to their behaviours that provide a “whole‐body” response to temperature changes. Although freshwater fish have been detected as moving in response to temperature changes to access habitats that provide their thermal optima, there is a lack of integrative studies synthesising the extent to which this is driven by behaviour across different species and spatial scales. A quantitative global synthesis of behavioural thermoregulation in freshwater fish revealed that across 77 studies, behavioural thermoregulatory movements by fish were detected both vertically and horizontally, and from warm to cool waters and, occasionally, the converse. When fish moved from warm to cooler habitats, the extent of the temperature difference between these habitats decreased with increasing latitude, with juvenile and non‐migratory fishes tolerating greater temperature differences than adult and anadromous individuals. With most studies focused on assessing movements of cold‐water salmonids during summer periods, there remains an outstanding need for work on climatically vulnerable, non‐salmonid fishes to understand how these innate thermoregulatory behaviours could facilitate population persistence in warming conditions.