Temperature determines early-life success of burbot Lota lota eggs.

Temperature strongly regulates early-life development of freshwater fishes, influencing embryogenesis, hatching success and larval survival. Cold-water species, including burbot Lota lota, are particularly sensitive to warming, yet information on the thermal requirements of their early-life stages remains limited. We experimentally quantified the effects of incubation temperature on eggs from multiple females of a Western-European burbot population. Eggs were incubated at five constant temperatures (2, 4, 6, 8, 10°C), and developmental outcomes, including hatching success, abnormal development and incubation time, were recorded. Hatching success was highest at intermediate temperatures (4 and 6°C) and substantially reduced at low (2°C) and high (8 and 10°C) temperatures, with highly elevated mortality and deformities at temperature extremes. Incubation time decreased with increasing temperature, reflecting accelerated development, but higher temperatures reduced developmental stability. Female identity significantly influenced developmental outcomes, and this effect interacted with incubation temperature, indicating that female-specific responses varied across thermal conditions. These results reveal a narrow thermal window for successful burbot embryogenesis and provide critical information on temperature thresholds for early-life stages, with direct relevance for habitat assessment, conservation, captive breeding and reintroduction programmes. Populations in temperate European rivers may be particularly sensitive to warming, emphasizing the importance of considering both thermal conditions and temperature-dependent variation among females when evaluating recruitment potential.