Critical Thermal Maximum

Critical thermal mass is measured by the temperature at which a given species may become unorganized in locomotion and that which will subject the animal to death. This is particularly true if the species has limited mobility and lacks the ability to seek a microhabitat of reduced thermal stress. Fish are often used to determine thermal tolerance because when they are in a temperature just slightly below critical thermal mass, they float belly up, so this temperature can be measured without killing the animal. All animals respond to a critical thermal maximum in different ways. Thermal end points are used.  Since it is generally easy with  fish, they are used in this experiment to help explain how critical thermal maximum works. This is done without harming the fish also.

The lab study done supports the belief that when fish hit critical thermal mass, they float belly up. These lab results obtained are further supported by Benfey and McCabe (1997) showing that the temperature of water affects fish that have reduced aerobic capacity and cannot get away to a cooler temperature. The increase in temperature reduces the amount of oxygen in the water as well as decreasing the hemoglobin-oxygen affinity. Galbrath, Adams,  Martin (2004) support the results of this experiment in their study of juvenile rainbow trout.  They exposed these fish to tanks of heated water and the end results were the same, the fish went belly up and temperatures were recorded.

In conclusion, this is an excellent short term study to show the  results of an animal when the temperature of its habitat is changed, especially when that animal cannot get away from the temperature change. This experiment is well suited to introduce the results of animal reaction to global temperature changes.


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