iGo PISCES 



Iceland to the Nile. In studying the fishes of the New Jersey salt 

 marshes during the winter the author found that small miyinows dug 

 from their burrows and brought into the laboratory in stiff, immobile 

 condition would revive in a short time. 



Britton ^ studied the freezing, overwarming and resuscitation of 

 the eel, skate, flounder and cod. When the temperature exceeded 

 30° C, or went below — 1° C. the fish became immobile and finally 

 the heart stopped beating. Resuscitation was readily effected in 

 many cases by transferring the fish to water of the normal tempera- 

 ture, about 16° C. In one case a skate, Raia laevis, was exposed for 

 " sixteen hours in a refrigerator to a temperature as low as — 20° C, 

 the whole of the fish being solidly frozen," and on gradual thawing 

 the heart beat returned to a slow regular thythm, but the animal 

 did not fully recover. At the lower temperatures, 6° C. to 10° C, 

 the respiratory action was almost coincident with heart beat. 



Reaction to Temperature Change. — One of the greatest factors 

 in the behavior of fishes is their response to temperature change. 

 We find that, by means of heat and cold corpuscles in the skin^ fish 

 proceed towards warmer or cooler water, and that it is the relative 

 temperature that determines their activity. Herring are sensitive 

 to very slight temperature changes, according to Shelford and 

 Powers (191 5), reacting to differences as small as 0.2° C. It has 

 been shown that temperature changes influence the reactions of 

 fishes to lights salinity^ Ph and to internal factors such as the de- 

 veloping gonads. Unquestionably this sense is the greatest single 

 factor that we find influencing the metabolism and behavior of 

 fishes. It must even be considered in connection with the instincts 

 of the species. 



Electric Organs. — In the Elasmobranchs we find electric organs 

 present in the torpedo ray. The electric eel is a Teleost with the 

 power to shock the unwary. With but one exception, electric 

 organs are composed of metamorphosed muscles and retain their 

 original nerve endings. 



Phosphorescent Organs. — The highest development of piscine 

 phosphorescent organs is in fishes inhabiting the depths of the sea. 

 A luminous organ in the fish is a collection of gland cells usually 

 forming the lining of a series of radially arranged tubules in the 

 deeper portion of the organ. The luminous organ contains ganglion 



' Britton, S. W. 1924. The effects of extreme temperatures on fishes. Am. Jour, 

 of Physiol., vol. 67, no. 2, pp. 411-421. 



