TO WHAT EXTENT DO ‘HIGH’ WATER TEMPERATURES AFFECT THE PHYSIOLOGY OF ATLANTIC SALMON?

Increases in average water temperatures and decreases in water oxygen levels (hypoxia), and more frequent and extreme warmin g events (i.e., heat waves), are occurring with climate change. Thus, there is an urgent need to understand the effects of prolonged

 and short-term warming on the physiology of cultured fishes, including Atlantic salmon ( Salmo salar). This is particularly true with regard to Tasmania and  Atlantic  Canada where water temperatures have approached or  exceeded 20°C, in combination with hyp oxia, and  negative effects on production and fish health ( including large-scale mortalities) have been reported.

Over the past few years, we have used a  multilevel (e.g.,

whole animal , biochemical, genomic, epigenetic) approach, and several experimental paradigms, to understand how high temperatures alone, and

 when combined with moderate hypoxia (60-70% air sat.), impac t salmon physiology and

production characteristics under realistic temperature scenarios (e.g.,

using an ITMAX test ;  a 1°C

 increase week-1 from 10°C ).

In this presentation,  we  will  show that  while stress gene expression in salmon begins to be affected at 16°C, and feeding decreases dramatically as temperatures approach 20°C, there is little/n o evidence that this temperature, even when  prolonged or combined with moderate hypoxia, results in mortalities .  The salmon’s capacity to mount an innate immune response is not compromised at these temperatures and

plasma cortisol levels (indicative of a secondary stress response) do not increase until 21-22°C .  Finally, in lab-based experiments, mortalities only begin when the fish reached

21°C ,  and even at 23°C mortalities  are only ~ 30% .

Through this research, we have also been able to identify epigenetic and genomic markers of temperature and hypoxia tolerance in salmon (e.g. Figure 1), and have identified populations/ families of salmon that have critical thermal  maximum (CTMAX) and ITMAX

 values of ~28°C and 25°C, re spectively. This should assist in the development genetic and other markers for use in selecting fish  that are more tolerant of these conditions and for evaluating fish health .