Temperature Acclimation and the Nervous System in Fish

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Abstract
The cold-blocking temperature of a simple reflex in goldfish (Carassius auratus) and bluegills (Lepomis macrochirus) was 10,° 5° and 1° C. respectively for fish acclimated to 35°, 25°, and 15° C. The response of 5° C. fish was not blocked at 1° C. Similar results were obtained with goldfish in which the spinal cord had been cut immediately posterior to the medulla. Conditioned inhibition of respiration in goldfish acclimatized to 30°, 25°, 15° and 5° C. was blocked at 20°, 15°, 10° and 1° C. respectively. A conditioned avoidance response of goldfish acclimated to 25° C. was blocked at 15° C. The cruising speed of green sunfish (Lepomis cyanellus) is related to the ambient temperature, and the upper and lower temperatures at which they do not swim are related to their thermal history. Peripheral nerves of bluegills and green sunfish acclimated to 25° C. continued to conduct impulses at temperatures below 5° C. It is concluded that the site of cold-block is in the central nervous system.