THE FRIGHT REACTION IN NORTH AMERICAN FISH

The fright reaction was found in five species of North American Cyprinidae including the predaceous northern squawfish, and in two species of Catostomidae. The threshold for Cyprinidae is 1/1000 N ("normal") extract or lower, that for Catostomidae at least a 1/100 N extract. The cyprinid species reacted very strongly to extract from other Cyprinidae but less strongly to catostomid extract; catostomid species reacted strongly to extract from other Catostomidae but less strongly to cyprinid extract. Salmon extract did not produce any reaction in Cyprinidae or Catostomidae. The epidermis of all species studied contained alarm substance cells; the epidermis of the Catostomidæ was very similar to that of the Cyprinidae. There was a relationship between number and size of the alarm substance cells (histology) and the quantity of alarm substance in the fish skin (physiology). The ability to respond to the alarm substance first appeared in young redside shiners at an age of 42 days, in young zebrafish at an age of 32 days, when the fish were kept at 26 °C.