Critical thermal maxima of diploid and triploid brook charr, Salvelinus fontinalis

The purpose of this experiment was to determine whether diploid and triploid brook charr, Salvelinus fontinalis, differ in their critical thermal maxima (CTM). Two age classes were tested (underyearlings, having average weight of 25 g, and yearlings, having average weight of 668 g) at two rates of temperature increase (2 degrees C h(-1) and 15 degrees C h(-1)). No effect of ploidy on CTM was found. Fish exposed to the faster rate of temperature increase had higher CTM values than those exposed to the slower rate (underyearlings: 29.5+/-0.1 degrees C versus 29.1+/-0.1 degrees C in one trial and 29.8+/-0.1 degrees C versus 28.3+/-0.1 degrees C in a second trial; yearlings: 29.3+/-0.1 degrees C versus 27.7+/-0.1 degrees C in two trials, p<0.001 in all cases). Underyearlings had higher CTM values than yearlings (29.2+/-0.1 degrees C versus 28.5+/-0.1 degrees C, p<0.05). Female yearlings, which were immature, had higher CTM values than males, which had previously matured as one-year-olds (28.8+/-0.1 degrees C versus 28.3+/-0.1 degrees C, p<0.001).