Effects of acclimation temperature, season, and time of day on the critical thermal maxima and minima of the crayfish Orconectes rusticus

Turtles acclimated to temperatures between 3 and 19 degrees C were placed in a thermal gradient. The animals usually selected temperatures above 28 degrees C within 1 h after placement in the gradient, attaining a final thermal preferendum between 31 and 33 degrees C. Turtles placed in the gradient for extended periods of time were more active during the day; the temperature selected was not related to activity or time of day. Turtles were transferred from a constant temperature bath at 10 or 30 degrees C to a calorimeter at 30 or 10 degrees C. Mean body temperature (Tb) and temperatures of the heart (The), brain (Tbr), and cloaca (Tcl) as well as heart rate were continuously monitored. In a 0.76-kg turtle, temperatures increased to two-thirds of the final difference between the initial temperature and the final temperature in the following times (min): Tb, 5.5; The, 6.0; Tcl, 9.0. The increase in Tbr varied depending on whether the head was extended or retracted. Rapid changes in ambient water temperature had relatively little effect on the heart rate of a submerged turtle. Heart rates were closely related to The and were practically independent of brain temperature.

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Seasonal changes in the critical thermal maxima of fantail (Etheostoma flabellare), greenside (Etheostoma blennioides), and rainbow (Etheostoma caeruleum) darters

Canadian Journal of Zoology ◽

10.1139/z85-241 ◽

1985 ◽

Vol 63 (7) ◽

pp. 1629-1633 ◽

Cited By ~ 14

Author(s):

Ihor Hlohowskyj ◽

Thomas E. Wissing

Keyword(s):

Seasonal Changes ◽

Acclimation Temperature ◽

Seasonal Differences ◽

Etheostoma Flabellare ◽

Significant Relationships ◽

Critical Thermal Maxima ◽

Etheostoma Blennioides ◽

Fantail Darter ◽

Rainbow Darter ◽

Etheostoma Caeruleum

Seasonal critical thermal maxima (CTMax) were determined for greenside (Etheostoma blennioides), fantail (Etheostoma flabellare), and rainbow (Etheostoma caeruleum) darters. Mean CTMax values for field-acclimatized greenside darters ranged from 26.2 °C in March to 35.1 °C in September. The values for fantail and rainbow darters were 30.8–36.0 °C (March–July) and 30.0–36.4 °C (April–July), respectively. CTMax values for the three species were significantly correlated (P < 0.05) with field water temperature (greenside darter, r = 0.970; rainbow darter, r = 0.964; fantail darter, r = 0.968). Fish acclimated at 10 and 20 °C in the laboratory exhibited significant seasonal changes in CTMax, with the highest values occurring in the summer. Except for fantail darters tested in summer, the three species showed significant relationships between CTMax and acclimation temperature. Seasonal differences were also observed in the slopes of the relationships between CTMax and acclimation temperature. The highest slopes occurred in spring, autumn, or both. Differences in the tolerance of darters to high temperatures and adjustment of tolerance to high temperature may influence their distributions in streams.

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