Temperature Preferences and Critical Thermal Limits of Burbot: Implications for Habitat Selection and Ontogenetic Habitat Shift

In large lakes, burbot Lota lota utilize several habitats during their ontogenesis. While juveniles are typically littoral dwellers, adults often prefer the cold profundal waters, especially during the summer months. Such distinct seasonal or ontogenetic habitat shifts are often induced by proximate abiotic factors that guide the fish toward another habitat in which either physiological performance is optimized or survival is increased. Temperature is often considered to be such a factor, especially in cold‐stenothermal species. In thermal gradient experiments, the effects of the acclimation temperature (AT) on the preferred temperature (PT) and the critical thermal maximum and minimum of burbot were studied. A significant nonlinear relationship was found between PT and AT in small (10−20 cm total length) burbot (SEs in parentheses): PT = −2.1363 (±0.5455) AT + 0.0732 (±0.0207) AT 2 + 26.2708 (±3.2075). The final temperature preferendum was 11.4°C. For large (20−30 cm) burbot, no such relationship between acclimation temperature and preferred temperature was found, and a final temperature preferendum of 14.2°C was calculated. Both size‐classes showed a positive linear relationship between the critical thermal maximum (CTMa) and AT: CTMa = 0.3254 (±0.0198) AT + 25.1106 (±0.2676) ( R 2 = 0.94) for small burbot, and CTMa = 0.3688 (±0.0276) AT + 24.2986 (±0.3742) ( R 2 = 0.91) for large burbot. A critical thermal minimum of 3.3°C was found for small burbot acclimated to 19.6°C. The results show that even during summer the littoral water temperature in Lake Constance is very unlikely to force juvenile burbot towards the cold profundal zone. However, the data provide good evidence that changes in water temperature in spring do act as a trigger for the juveniles to leave the littoral to avoid a thermal trap during summer.