238 The Lije Story of the Fish 



where they were unknown. It took him some time to realize 

 how dangerous this might be, to learn that a species which 

 in one place had proved beneficial (to man) might go out of 

 control in another place where the natural checks on its 

 numbers were missing. The present unpopularity of the carp, 

 which was brought into North America with such enthusiasm, 

 attests the damage which can be done and the difficulty of 

 undoing it. 



Fortunately, trout introductions have done very little 

 harm and considerable good. These fish have been found to 

 be among the easiest of all animals to transplant because they 

 can be shipped almost any distance in the form of "eyed" 

 eggs — eggs which have developed to the point where the 

 eyes of the embryo show as black dots through the envelop- 

 ing membrane. At this stage they are very hardy and do not 

 need to be in water. Packed in damp moss, they will survive 

 for weeks. For journeys of very long duration, advantage 

 can be taken of the fact that the development is greatly 

 slowed by lowering the temperature. Brook trout eggs take 

 44 days to hatch at 50 degrees Fahrenheit, 100 days at 40 

 degrees, 145 days at 35 degrees. Rainbow take only 30 days 

 at 50 degrees, 86 days at 40 degrees. With the aid of refrig- 

 eration it was possible, even before the days of air travel, to 

 ship brown trout eggs from Europe to America, rainbow 

 from America to Europe, New Zealand, and Africa. 



While the intercontinental transplantations are the most 

 spectacular, important introductions have been made on a 

 much smaller scale. The simplest and shortest occurred 

 when California cattlemen took a dozen of the famous golden 

 trout out of the limited stream system in which alone that 

 form was found and carried them in a coffee pot four miles 

 across a divide to dump them into an entirely different water- 

 shed. From these rudely treated forebears have come all the 

 golden trout which have been planted in other parts of Cali- 



