infection and point to the caution with which 

 chemotherapy experiments must be designed 

 in order not to terminate them prematurely. 



Although the disease proved transmis- 

 sible by abrasion, our observations of the 

 response of the fish led us to believe that re- 

 peated inoculation was undoubtedly more effec- 

 tive than single inoculation in achieving this 

 transmission. Even with the more effective 

 abrasion (manual), the bacterium was not found 

 in the kidneys of all the fish. This suggested 

 either that infection did not occur or that it did 

 but that recovery ensued. In any event, con- 

 sidering the fractional success and the time and 

 effort involved, abrasion was judged to be less 

 efficient than the severely artificial and highly 

 fatal method of hypodermic injection. 



The results of the experiment demon- 

 strated that kidney disease was not transmitted 

 to eastern brook trout by feeding. This cor- 

 roborates the work of Snieszko and Griffin (1955) 

 who did not find the disease transmitted to the 

 same species of fish by feeding. In all, 300 

 fish, fish shown to be susceptible to infection 

 by other routes, were fed the bacterium for a 

 total of 102 days, and in no instance was trans- 

 mission indicated. These are different results 

 from those obtained among salmon under pre- 

 sumably different conditions on the West Coast . 

 Admittedly there are great differences between 

 the salmon and trout which are subject to kidney 

 disease, but as -yet -unknown environmental 

 factors may also be involved. As an example, 

 kidney disease appears to be endemic in some 

 trout -cultural stations in the eastern United 

 States. 



Although highly susceptible eastern brook 

 trout are propagated in the facility operated in 

 conjunction with our laboratory, there have been 

 but 2 known occurrences of the disease, and in 

 both instances fewer than 10 infected trout were 

 found in circular pools in which thousands of 

 trout were present. 



In attempting to relate successful exper- 

 imental infections achieved in conjunction with 

 abrasion to hatchery occurrences among trout, 

 several possibilities should be considered. The 

 dermal route seems more likely to be involved 

 in hatchery transmission than the oral route. 



In trout -cultural stations such dermal entry is 

 theoretically possible following abrasion in 

 masonry facilities or following biological penetra- 

 tion or lysis by any of several bacteria, fungi, or 

 parasites to which these fish are hosts. An 

 animal vector is not to be excluded as a possib- 

 ility, but mere exposure of host tissue (mechanical 

 or biological) is an equally attractive speculation. 



EFFECTS OF TEMPERATURE ON KIDNEY 

 DISEASE INFECTIONS 



Mortality from kidney disease usually 

 shows periodicity, but the more specific effects 

 of temperature are less well established. Belding 

 and Merrill (1935), the first to report on a disease 

 which was apparently kidney disease, noted its 

 seasonal occurrence and stated that the curve of 

 mortality tended to follow the curve of rising water 

 temperature. Earp et al. (1953) stated, "Water 

 temperature is a major factor in determining the 

 severity of the disease." They found that most 

 outbreaks occurred during autumn and winter, 

 the season of declining water temperatures, ana 

 that there was an Increased mortality at the low 

 temperatures. The most explosive outbreaks, 

 however, were found to occur at warmer water 

 temperatures. According to Snieszko and Griffin 

 (1955), peak mortality at New Hampshire occurred 

 during the spring - presumably when water tern - 

 peratures were cold but rising. Wood and Wallas' 

 data (1955) show salmon experiencing increasing 

 mortality during periods of falling water temper- 

 atures, but they did not call particular attention 

 to this . It was to determine more specifically 

 the effect of temperature that the following ex- 

 periment was conducted. 



Material and Methods 



Uniformly sized eastern brook trout aver- 

 aging 66 grams each at the start were used for 

 this experiment. Diet and rate of feeding were 

 the same as in the preceding experiment. One 

 unit of 2 troughs was kept at 7° C; a second unit 

 of 2 troughs was kept at 12.5° C. Water flow was 

 adjusted within the limits Imposed by the necessity 

 of having to refrigerate one pair of troughs . 

 Troughs at 12.5° C. received 900 ml. per minute; 

 those at 7° C. received about 600 ml. per minute. 

 Resulting average ammonia levels as periodically 

 determinecf by nessleri7ation were about 0.8 p.p.m. 

 at 7" C. and 0.4 p. p.m. at 12.5° C. 



