The potential for heat shock exposure during early development to alter the molecular responses to subsequent exposure to heat stress in the rainbow trout

Fish are ectothermic animals with temperature playing a key role in their health, growth and survival. Greater occurrence of heat waves and temperature extremes, as a result of global climate change, has the potential to impact both wild and farmed populations. Within aquaculture, production is threatened by a multitude of stressors, including adverse temperatures. The propensity for environmental temperature during early embryo development to influence later life transcriptomic responses has been observed in numerous animal species, and, if harnessed, could provide a method for inducing phenotypic changes in adult aquaculture species. We hypothesise that exposure of rainbow trout embryos to temperature stress results in alterations to transcriptional responsiveness upon re-exposure later in life. To test this hypothesis, we exposed embryos to a range of different heat shock treatments during early development and then analysed their response to thermal stress at five days post hatch (dph), in comparison to naïve fish that experienced no early development heat shock. Hsp70a and hsp70b transcription was measured (using RT-QPCR) as a biomarker for thermal stress response. Significantly greater transcriptional induction of hsp70a in response to post-hatch thermal stress was found in heat shocked larvae compared to naïve larvae (p = 0.0085). The timing, intensity and duration of the initial heat shock was not found to statistically influence the alteration of hsp induction when compared to that of naïve larvae. Together, these results support our hypothesis that heat shock during early development has the potential to affect responsiveness to the same stressor later in life. Future studies should focus on understanding whether this could be utilised to increase robustness of fish in aquaculture.