Increased thermal tolerance does not alter behavioural performance in zebrafish larvae following rapid warming

Zebrafish were reared at 3 developmental temperatures before being acutely ramped up to higher temperatures where behaviour, metabolism, and biochemistry assays were performed. We explored the hypothesis that altered temperature during the embryonic window could influence thermal performance in zebrafish. Zebrafish embryos were maintained at either 24, 28, or 32°C until 2 days post-fertilization, and then transferred to a common garden temperature of 28°C until 5 days post-fertilization. Elevations in embryonic temperature led to an expected precocious development. At 5 days post-fertilization, we recorded the critical thermal maximum (CTMAX) as a measure of thermal tolerance. Fish reared at 32°C could withstand higher temperatures than fish reared at both colder temperatures. To test whether the embryonic temperature influenced larval performance, we acutely raised the temperature of larvae and measured oxygen consumption and behaviour at temperatures below their CTMAX (28-40°C) at a rate of 0.3°C/min. Fish reared in colder temperatures had higher oxygen consumption when temperatures were acutely raised. Exploratory behaviour was highest in fish acutely raised to 32-34°C, decreasing beyond 34°C, with colder rearing lowering movement. Responses to light and acoustic stimuli were maximal at 32°C. Together, temperature during the embryonic window influenced the absolute thermal tolerance of larvae but had more nuanced impacts on acute thermal performance.