Thermal imprinting modifies adult stress and innate immune responsiveness in the teleost sea bream

The impact of thermal imprinting during development on the plasticity of the hypothalamic-pituitary-interrenal (HPI) axis and stress response in an adult ectotherm, the gilthead sea bream (Sparus aurata, L.), was assessed. Fish were reared under 4 thermal regimes and the resulting adults exposed to acute confinement stress and plasma cortisol levels and genes of the HPI axis monitored. Changes in immune function, a common result of stress, was also evaluated using histomorphometric measurements of melano-macrophages centres (MMCs) in the head kidney and by monitoring macrophage related transcripts. Thermal history significantly modified HPI responsiveness in adult sea bream when eggs and larvae were reared at a higher than optimal temperature (HT, 22 ºC) and they had a reduced amplitude in their cortisol response and significantly up-regulated pituitary pomc and head kidney star transcripts. Additionally, after an acute stress challenge immune function was modified and the head kidney of adult fish reared during development at high temperatures (HT and LHT, 18-22 ºC) had a decreased number of MMCs and a significant down-regulation of dopachrome tautomerase. The impact of thermal imprinting during development on the physiology of adult sea bream was evident even in the absence of acute stress and eggs and larvae reared at 22 ºC and 18 ºC, respectively (high-low thermal regime, HLT) had increased plasma glucose, sodium and potassium relative to adults from eggs and larvae maintained at a constant temperature (22 ºC or 18 ºC). Overall the results demonstrate that temperature during early development impacts on the adult HPI axis and immune function in a teleost fish.

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