The Fungus of Salmon Disease. 77 



hardly any vitality, and natural death is at such a time not un- 

 common. The spawning operation, when the fish are con- 

 tinually routing among the gravel in the running water, would 

 naturally result in opening the epidermis and exposing the skin ; 

 and it is also said that fish during spawning time will fight 

 viciously. The condition of health in fishes, I am inclined to 

 think, has much to do with the salmon disease, and one of the 

 first consequences of a low vitality may be a slow or imperfect 

 excretion and epidermic formation. Sickly fish of all kinds are 

 often attacked and die of fungus, when the real exciting cause 

 of death was a low vitality occasioned by sickness or old age ; 

 and our fungus often breaks out in aquariums, and kills such 

 fish. Fish that die in rivers are probably the legitimate food of 

 the fungus, and one of its special means of propagation during 

 long winter periods, when rapid development is impossible, and 

 when the species also runs the extra chance of extermination 

 owing to the deposits of mud during floods in the quiet eddies, 

 where the spores would be likewise deposited. 



Is not the possibility of the deterioration of a stock of salmon 

 also an open question, when we know that they always 

 return to the same rivers in which they were bred ? It is pos- 

 sible for a river greatly to change in a period of years. A good 

 system of surface drainage adopted on the banks of a river and 

 its tributaries, where for years before the water was allowed to 

 collect and gradually flow off, would lessen the volume of a 

 small river to a considerable extent, and account for the run- 

 ning dry of springs ; a succession of dry seasons on a water 

 naturally impure might also promote the same unfavourable con- 

 dition by concentrating these impurities ; and with such a 

 state of things existing, would not a stock of fish deteriorate, 

 and become more liable to this fungoid pest ? It is certain 

 that salmon vary very much in appearance, and that their 

 strength (as evidenced by angling experience) may vary also in 

 different rivers. Trout vary also in condition, vigour, and 

 size ; but while it is in all probability the feeding qualities of 

 the water in which they entirely live that cause the trout to 



