The Influence of Repeated Transient Heat Shocks on Development and the Stress Response of the Cold-Adapted Fish Species, Lake Whitefish (Coregonus clupeaformis)

Lake Whitefish (LWF) embryos develop at 2-6°C in the near shore environment and thus may be susceptible to industrial warm water discharges entering the surface waters. The aim of our research was to determine if transient heat shocks, which mimic thermal effluents, had detrimental or beneficial effects on LWF embryos. We exposed LWF embryos to repeated transient low-level heat shocks (transient heat shock: +9°C or +12°C every six days) followed by a high-level heat shock (+15°C or +18°C). To understand the effects of these heat shocks we examined both whole animal responses including daily rate of mortality, mean age at hatch and length at hatch as well as the cellular heat shock response. High-level heat shock seemed to increase daily rate of mortality and mean age at hatch, decrease embryo size at hatch and induce the heat shock response. Transient heat shock did not show any observable effect on the whole animal responses to a high-level heat shock, though; it was observed that transient heat shock attenuated the post high-level heat shock response. If this attenuated response is long-lived it may offer a protective advantage later in life history through an improved ability to deal with this and other stressors.