Temperature Perception and Responses 225 



southern Michigan. ^^ These fish arc now being successfully established 

 as far north as Winnipeg, Manitoba, Canada.^^ 



Sensitivity to Temperature Change 



Although there appears to be no specialized temperature receptors in a 

 fish's skin, there is little doubt that fish are capable of feeling relatively 

 slight changes in temperature. Sullivan ^'' describes an experiment in 

 which fish were fed at the same time that the temperature was slightly 

 raised so that feeding became associated with small rises in tempera- 

 ture.^^' ^^ After a training period, a temperature rise as small as 0.03° to 

 0.1°C would produce a feeding reaction. By the direct approach, employ- 

 ing electrophysiological equipment, it has been demonstrated that a rising 

 temperature (within the range of 4° to 17°C) increased the frequency of 

 rhythmatic impulses in trunk lateral line nerves, with about a two-fold 

 increase in frequency for each 4° temperature rise. 



After fish were shown to be sensitive to small changes in temperature, 

 the next approach was to see how they were affected by rapidly increasing 

 temperature. There was no response until a specific "response temperature" 

 of 27°C (80.6°F) was reached, when the fish suddenly began vigorous 

 swimming movements. ^^ In reverse, fish plunged into cold water reacted 

 immediately with violent bursts of activity followed by benumbed in- 

 activity.^^ 



Changes in temperature of a few degrees C, with time for the body of 

 the fish to equilibrate with the water (20 minutes), resulted in a little 

 movement at low temperatures, increasing as the temperature was raised 

 to a peak which occurred at the temperature that the species normally 

 selected in a temperature gradient. If the temperature were raised further, 

 activity decreased reaching a second low several degrees below the lethal 

 level.^^ If the temperature were increased further, movement again in- 

 creased to a second peak after which activity stopped abruptly and the 

 animal died. These experiments demonstrate the relationship of tempera- 

 ture to activity levels in fishes. Peaks of activity were modified to some 

 extent by exposure to low or high temperatures for extensive periods prior 

 to testing. 



Mortalities Caused by High Temperatures 



Fishes are seldom killed by high temperatures alone when out-of-doors 

 in natural waters ( see Chapter 3, p. 46 ) although Bailey ^ recorded such 

 a mortality of fishes in a part of Bass Lake, Livingston County, Michigan, 

 that had become separated from the main lake by a gravel ridge. At the 

 time of the kill the pond was about one-fourth acre with a maximum depth 

 of 5 inches. 



