CRITICAL THERMAL MAXIMA OF DIPLOID AND TRIPLOID BROOK CHARR, SALVELINUS-FONTINALIS

The purpose of this experiment was to determine whether diploid and tr iploid brook charr, Salvelinus fontinalis, differ in their critical th ermal maxima (CTM). Two age classes were tested (underyearlings, havin g 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 degr ees C h(-1)). No effect of ploidy on CTM was found. Fish exposed to th e faster rate of temperature increase had higher CTM values than those exposed to the slower rate (underyearlings: 29.5+/-0.1 degrees C vers us 29.1+/-0.1 degrees C in one trial and 29.8+/-0.1 degrees C versus 2 8.3+/-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). Und eryearlings 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 im mature, 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).