Effects of diel temperature fluctuation on the standard metabolic rate of juvenile Atlantic salmon (Salmo salar): influence of acclimation temperature and provenience

We assessed the metabolic response of juvenile Atlantic salmon (Salmo salar; JAS) originating from two rivers with different natural thermal regimes to different acclimation temperature (15 or 20 degrees C) and diel temperature fluctuation (constant: +/- 0.5 degrees C; fluctuating: +/- 2.5 degrees C). Diel temperature fluctuation (15 +/- 2.5 degrees C) near the thermal optimum (16 degrees C) for the species did not influence standard metabolic rate (SMR) compared with JAS acclimated to a constant temperature of 15 degrees C. Diel temperature fluctuation at 20 +/- 2.5 degrees C increased SMR of JAS from the warmer river by 33.7% compared with the same fish acclimated to a constant temperature of 20 degrees C. SMR of JAS from the cooler river held at fluctuating conditions had SMR that were 8% lower than SMR at constant conditions. The results suggest that the mean temperature to which JAS is exposed may affect their responses to diel temperature fluctuation and that this response may vary between populations originating from rivers with different natural thermal regimes. Results were used to develop the first empirical SMR model for JAS subjected to diel temperature fluctuation using fish mass (3-36 g wet) and temperature (12.5-22.5 degrees C) as explanatory variables.