156 TENTH ANNUAL REPORT OF THE 



crop is sought from the minimum of space. With trout this is of course a 

 marked departure from the natural condition, and one in which its unfav- 

 orable influence with respect to disease is readily apparent. In the presence 

 of the original micro-organisms of infection before any disease has occurred 

 the chances of their access to the body of the fish are increased ; and after 

 they have become established in even one fish the chances of propagation 

 of the disease by transferrence from fish to fish are enormously increased by 

 the proximity of the individuals. It is in this respect that crowding has its 

 most noticeable effect, though it is doubtless, in common with the other 

 conditions mentioned, not without its indirect influence in preparing the 

 way, in making a favorable ground, by a weakening of the resisting powers, 

 for those very enemies whose first attacks and later spread it aids directly. 



Crowding is here used in the sense of a proper, because necessary, con- 

 centration of fish in a given capacity of space and waterflow. The expres- 

 sion of this permissible concentration, numerically, for given area and flow 

 cannot, at least has not, yet been made and as so many factors enter in, a 

 simple general formula will probably not be obtained. Each fish culturist 

 by his judgment and experience arrives at an approximation and with 

 continued success it is easy to appreciate that he would be tempted to 

 increase the number from year to year, while his water supply and pond area 

 remain the same. Inevitably the danger line is sooner or later passed and 

 the condition may be described as overcrowding. 



With respect to Cold Spring Harbor the conditions of food, ponds, and 

 water supply were much as they had been in the past, but the number of 

 trout carried had been materially increased during the year preceding the 

 outbreak of disease. Here then is believed to be an application of the prin- 

 ciples above discussed, which are merely the extension to fish culture of 

 already well-known laws recognized in the science of human disease. Other 

 instances of trout epidemics following overcrowding are not wanting and will 

 continue to come under the observation of trout culturists. 



Among a stock of trout dying from this disease, or from any general 

 infection, a considerable portion may usually be saved by transferring them 

 to much larger quarters, as to a large natural pond of cold water or to a 

 reach of a natural stream in which they may be retained by screens. This 

 will not of course immediately put a stop to all loss among such trout. 



