Critical thermal maxima and acclimation rate of the tropical guppy Poecilla reticulata

Tropical guppies, Poecilia reticulata, collected from the canal of La Laguna Los Patos were acclimated over a four-week period at local water temperatures of 24-33degreesC to determine their critical thermal maxima (CTM) and death points (DP), as criteria of thermal tolerance. In addition, individual thermal tolerance times at a lethal temperature of 38.5degreesC were measured over 12 days for upward acclimation from 24 to 30degreesC and over 16 days for downward acclimation from 30 to 24degreesC to determine acclimation rate just before and after changing the acclimation temperatures. The CTM ranged from 38.95 to 40.61degreesC and the average DP varied from 41.22 to 42.86degreesC. Positive relationships were apparent between thermal tolerance and acclimation temperatures, and thus heat tolerance criteria (CTM and DP) were significantly different among acclimation temperatures. Individual heat tolerance times increased most rapidly during the first 6 hours of upward acclimation after transfer from 24 to 30degreesC, continued to increase another 5 days and fluctuated after initial acclimation was completed. The heat tolerance times of fish transferred from 30 to 24degreesC declined steadily over times, reaching a minimum at 14-16 days after transfer.