METHOOS OF INFECTING TROUT WITH KIDNEY DISEASE AND SOME 

 EFFECTS OF TEMPERATURE ON EXPERIMENTAL INFECTIONS 



In t±ie hatchery or rearing facility de- 

 voted to salmonid production, infectious 

 diseases often constitute a serious problem. 

 Kidney disease is one such infection; it is chron- 

 ic bacteremia which results in appreciable 

 losses among the commercially important Pacif- 

 ic salmon and among the three most important 

 species of hatchery -propagated trout. The 

 cause of the disease has been clearly establish- 

 ed. Although the causative bacterium is not 

 yet completely described, it is considered by 

 Ordal and Earp (1956) to be a Corynebacterium . 



The loss of these fish can be reduced or 

 eliminated by three general approaches: (1) 

 breeding disease -resistant stocks; (2) prevent- 

 ing the disease; and (3) treating infected fishes 

 when the disease does occur . 



Rational prevention of kidney disease 

 presupposes the knowledge of how the disease is 

 transmitted. Unfortunately, the means by which 

 kidney disease is transmitted is as yet unknown. 

 The second approach to the reduction of loss 

 from kidney disease, that of therapy, is severe- 

 ly limited because a satisfactory treatment of 

 the disease has not been found. 



The route by which an organism invades 

 or gains entrance to a host is termed its portal 

 of entry. Infectious diseases usually involve 

 one principal portal of entry. In fact, some in- 

 fections can of^cur only through a very particular 

 portal of entry. Knowledge of how a disease of 

 fishes can be established under artificial con- 

 ditions might well indicate the probably portal or 

 portals of entry under hatchery conditions . 



Thus far, trout can be experimentally in- 

 fected with kidney disease only by injection. 

 Phis method is severe and highly artificial . It 

 is desirable to have a less drastic method where- 

 by nearly natural infections with kidney disease 

 can be conveniently established among large 

 numbers of trout . 



Among genera, species, and even among 

 strains of a particular species of fish, differen- 

 tial susceptibility to a particular disease is well 

 known. Kidney disease is generally conceded Co 

 be more severe among Pacific salmon than among 

 trout. Eastern brook trout ( Salvelinus fontinal|s) 

 are more severely affected than rainbow trout 

 Salmo gairdneri ) . Nothing is known of the range 

 of virulence of the pathogen . 



As indicated by Snieszko (1954) in a re- 

 cent review of therapy of bacterial diseases of 

 fishes, temperature has been found to strongly 

 influence the course of such infections . There 

 is evidence that kidney disease is similarly 

 affected. 



The objectives of the research reported 

 here, therefore, were as follows: (1) to attempt 

 to uniformly infect large numbers of trout with 

 kidney disease by different methods and with two 

 different strains of the organism; (2) to observe 

 the course of infections and comparative success 

 achieved by the different methods and by the dif- 

 ferent strains of the organism; and (3) to deter- 

 mine the effects, if any, of different temperatures 

 on the course of the kidney disease infection. 



PORTALS OF ENTRY IN KIDNEY DISEASE 

 INFECTIONS 



Ulcer disease and furunculosis, two com- 

 mon bacterial diseases of trout, are routinely 

 transmitted to susceptible hosts by a single day's 

 feeding or by short-term contact with the causative 

 organisms . There is adequate evidence that the 

 same portals of entry are involved in natural arid 

 hatchery occurrences of these diseases. Exper- 

 imental infection with kidney disease has not 

 followed this pattern, and the observations whidh 

 have been made do not constitute a firm basis f{>r 

 postulating the portal or portals of entry of natural 

 infections . 



